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High resolution electron impact studies Thomas, Gary E. 1969

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HIGH RESOLUTION ELECTRON IMPACT STUDIES  by  GARY E. THOMAS B.Sc.  University  of B r i t i s h  .A THESIS SUBMITTED THE  IN PARTIAL  REQUIREMENTS  19 6 5  FULFILMENT OF  FOR THE DEGREE OF  DOCTOR OF in  Columbia,  PHILOSOPHY  t h e Department o f CHEMISTRY  Ke  accept  reauired  THE  this  thesis  t o the  standard  UNIVERSITY OF BRITISH January,  0  as c o n f o r m i n g  1969  Gary E. Thomas  1969 .  COLUMBIA  In  presenting  this  an a d v a n c e d d e g r e e the I  Library  further  for  agree  in  at  University  the  make  that  it  partial  freely  this  representatives. thesis  for  It  fulfilment  of  of  Columbia,  by  of  financial  gain  Q  ) S T R  f f g M  The U n i v e r s i t y o f B r i t i s h V a n c o u v e r 8, Canada  Date  F t " 6 • 6~  the  shall  Columbia  f  not  the  requirements  reference copying of  Head o f  understood that  written permission.  Department  for  extensive  granted  is  British  available  permission for  s c h o l a r l y p u r p o s e s may be  by h i s of  shall  thesis  I agree and  that  Study.  this  thesis  my D e p a r t m e n t  copying or  for  or  publication  be a l l o w e d w i t h o u t  my  ABSTRACT  A wide attachment electron the  such  beam  into  of  beam  has  processes  and  these  the  course  127°  be  work  electrostatic  the  observation  monopole  m easu rement negative  a  the  with  dependence  of  t he  a n d much  work,  instruments  to  distorted  the  the  gas.  cross  ensure by  by  was  was  taken  the  in  cross  effects.  "monoenergetic" sections  for  the  measurements,  constructed  during  A l l three  employed  selector  to  analyzer  permitted  of  positive  electron  the the  filter  electrons,  permitted  The measurement  that  spurious  the  a  make  scattered filter  sections  care  and  amounts  i o n i z a t i o n generated  interaction  not  relative  to  energy  inelastically  an  detail.  velocity  q u a d r u p o l e mass  of  used  electron  observing  cross  described.  An e l e c t r o n  of  some  designed be  of  relative  were  electron  beam.  or  to  and by  The use  in  and  by d i r e c t i n g  chamber  the  examined  were  scattering  studied  filled  instruments  the  electron  been  permitted  instruments of  inelastic  interaction.  to  the  a  a gas  the  Three  a  of  phenomena have  results  electron  variety  or  the  prime  in  its  energy  objective  design  section  the  beam  of  and  of  curves  the were  of  The and  ethylene  incident of  were  energy  singly  results  and are  expressions ionization also  forward  with  efficiency  an  helium  impact  curves  electron  ionization  several  were  beam  of  efficiency  theoretically  nitrogen  helium  having  obtained,  threshold  for  spectra  curves  and  the  derived  laws. and  an  The  positive  oxygen  were  obtained.  the  examination  the  hexafluoride  obtained  as  an  gas.  for  six  measurements  ionization  dissociative  ion  pair  energy  dependence  of  parent  the  the  scattering  sample  and  the  capture,  processes of  and/or  the  has  cross  fragment  been  made  section negative  s ions  molecules. Finally,  inelastic  of  capture  production  f ro m n i n e  such  The  charged  electron  scattering  using  eV .  compared  determining  the  50  doubly  non-dissociative  for  recorded  of  for  An  by  inelastic  generation  events  electron  The  were of  been  scavenger  threshold  atomic  potential  has  of  the  out  sample.  energy  studied in  electron  and m o l e c u l a r carried  zero  by  using  a mixture impact  species.  below  electrons  and  from  sulfur  with  spectra In  all  above  the  were cases,  TABLE OF  CONTENTS  Page  ABSTRACT  i i  ACKNOWLEDGEMENT CHAPTER 1.1  xi  ONE - INTRODUCTION Electron  1  Impact P r o c e s s e s  2  1.1.1  Elastic Collisions  2  1.1.2  Superelastic  3  1.1.3  Inelastic  1.1.4  Electron  1.2  Electron  1.3  Instrumental  Collisions  Collisions  3  Capture  4  Scavenging  5  Methods  i n Electron  Collision  6  Studies 1.3.1  Electron  Sources  6  1.3.2  Electron  Monoehromators  7  The RPD Gun  Theoretical  Deflection  1.3.3 1.4  8 Electron  Monqchromators  Analyzers  Mass S p e c t r o m e t e r s  Experimental  O b j e c t i v e s and S t u d i e s  11 13 15 18  V  P a  CHAPTER  TWO -  THEORETICAL  2.1  General  Collision  2.2  Electron  2.3  Electron  Theory  21  Impact  Excitation  25  Impact  Ionization  29  Threshold  Laws  2.3.2  Classical  Calculations  Cross  2.4  Formation  of  Dissociative  2.4.2  Ion-Pair  2.5  Theory  Electron  CHAPTER-THREE  -  Ionization  of  Ionization  Electron  Negative  Impact  Ions  Attachment  46 49  Electron  Negative  41 45  Formation  of  31  37  - Non-Dissociative  2.4.4  Direct  Sections  2.4.1  2.4.3  for  A u t o i o n i z a t i o n by  The  e  20  2.3.1  2.3.3  g  Ion  Capture  Formation  50 51  Scavenging  55  INSTRUMENTAL  59  3.1  The  Electrostatic  3.2  The  Quadrupole  3.3  The  Instruments  Analyzer  Electric  59  Field  Mass  Filters  62 68  3.3.1  The  Total  Ionization  3.3.2  The  Monopole Instrument  74  3.3.3  The  Quadrupole  81  3.3.4  Electronic  3.4  Method of  Instrument  Circuits  Equipment Operation  Instrument  and  69  Ancillary 82 87  vi  Page  CHAPTER 4.1  FOUR  -  RESULTS  Inelastic  AND D I S C U S S I O N  Scattering  91 91  4.1.1  Helium  91  4.1.2  Ethylene  93  4.2  Positive  Ions  96  4.2.1  Helium  4.2.2  Nitrogen  108  4.2.3  Oxygen  111  4.3  Negative  96  Ions  114  4.3.1  0"  From  Oxygen  4.3.2  0*  From  Carbon  4.3.3  0"  From  Nitrous  4.3.4  Br"  From  Bromine  4.3.6  CI"  From  Carbon  4.3.7  The  Methyl  4.3.8  I"  4.3.9  Br"  4.3.10 4.4  From  CI"  Electron  From  Monoxide Oxide  Tetrachloride  Iodide  Methyl  116 119 121  Halides  Methyl  From  114  Bromide  Methyl  Scavenging  Chloride  128 131 132 135 137 140  4.4.1  Helium  140  4.4.2  Hydrogen  146  4.4.3  Xenon  149  4.4.4  Carbon  Dioxide  154  4.4.5  Carbon  Oxysulfide  157  4.4.6  Carbon  Disulfide  160  vi i  Page REFERENCES  163  APPENDIX  I  176  APPENDIX  II  180  LIST  OF  TABLES  Page I.  Summary  of  Studies  Performed  19  LIST  OF F I G U R E S Page  Potential  2.  Quadrupole  and  Monopole  Mass  3.  Quadrupole  and  Monopole  Stability  4.  Exploded  5.  The  Total  6.  The  Monopole  7.  A n IE l e c t r o n  8.  Residual  9.  The  Selector-Analyzer  10.  The  Monopole  11.  The  Data  12.  The  Inelastic  Scattering  Spectrum  of H e l i u m  1 3.  The  Inelastic  Scattering  Spectrum  of  14.  The  Ionization  15.  Gas  Pressure  16.  Comparison  of  1.127  17.  Comparison  of  1.5  18.  Comparison  of  Temkin  19.  Comparison  of  Classical  Helium  Energy  .  1.  View  of  Curves  a  127°  Ionization  Gas  Mass  Power  Retrieval  Electron'  Diagram  66  Selector  70  Instrument  .  73 75  Distribution  79  Spectrum  80  Electrical  Circuit  83  Supply  86  System  88  Efficiency  Curve  of  Ethylene  Helium  92 94 97 99  Test  Results  64  Spectrometers  Instrument Energy  47  Law Law  With  with Law  Helium  Helium  with  Results  Results  Helium  Calculations  Results  101 102 103  with 106  X  Page  20.  The  Double I o n i z a t i o n  of  Helium  21.  The  Ionization  22.  Autoionization  in  23.  The  Ionization  Efficency  24.  The  Formation  of  0"  from  Oxygen  25.  The  Formation  of  0"  from  Carbon  26.  The  Formation  of  0"  from  Nitrous  27.  The  Formation  of  Br"  28.  s  29.  S F  Efficiency  107  Curve  for  Nitrogen  Nitrogen  110  Curve  from  for  Oxygen  ^  e  a  ^  from  the  Monopole  6~  ^  e  a  ^  from  the  Quadrupole  112 115  Monoxide Oxide  Bromine  ^6*  120 122  Instrument Instrument  126  Formation  of  Cl"  31.  The  Formation  of  I"  32.  The  Formation  of  Br"  from  Methyl  Bromide  136  33.  The  Formation  of  Cl"  from  Methyl  Chloride  138  34.  The  SF  35.  Comparison  Scavenging of  E^'^  Methyl  Curve with  Tetrachloride  125  The  from  Carbon  117  30.  &  from  109  Iodide  of  Helium  the  Helium  Scavenging 143  0  37.  of  Scavenging  Results  SF,  E  12 7  Comparison  The  133  141  Results  36.  129  '  with  the  Helium 144  Scavenging  Curve  of  Hydrogen  147  6  38.  The  SF  6  Scavenging  Curve  of  Xenon  150  39.  The  SF  6  Scavenging  Curve  of  Xenon  153  40.  The  SF  6  Scavenging  Curve  of  Carbon  Dioxide  155  41.  The  SF^  Scavenging  Curve  of  Carbon  Oxysulfide  158  42.  The  SF^  Scavenging  Curve  of  Carbon  Disulfide  161  ACKNOWLEDGEMENT  I expr ess his  would  this  C.  A.  support  work,  and  McDowell In  staffs  of  the  Department  construction  in  to  for  the  British  Canada  for  thank  in  their  D.  advice  I  wish  I  and  generous  C.  for  E.  Brion  throughout  and  Frost  the  and  course  Professor  suggestions.  acknowledge  gratefully  and  Electronics  Workshops  for  like  the  to  C,  their  expertise  M r . W.  preparation  would  opportunity  to  for  laboratory  Columbia  Dr.  instruments,  the  the  to  Dr.  Chemistry  the  this  assistance  their  Finally, of  take  Mechanical  of  of  assistance  colleagues  and  addition,  the  his  to  my d e e p a p p r e c i a t i o n  welcomed  of  like  of  this  their to  Stewart thesis,  continued  thank  National  financial  B.  in  the  Research  of  the for a n d my  support.  University Council  assistance.  of  CHAPTER ONE INTRODUCTION  The  i n t e r a c t i o n of e l e c t r o n s with matter i n the gas  phase has r e c e i v e d a great deal of a t t e n t i o n s i n c e e a r l y i n the twentieth century. by  I n t e r e s t i n t h i s s u b j e c t was prompted  e a r l y o b s e r v a t i o n s o f Franck  and Hertz that an e l e c t r o n  beam behaved i n much the same way as a l i g h t beam i n i t s passage through  a gas-filled  chamber.  would s u f f e r a t t e n u a t i o n * and such i o n i z a t i o n and molecular e l e c t r o n impact* and  That  i s , the beam  e f f e c t s as f l u o r e s c e n c e ,  d i s s o c i a t i o n c o u l d be induced by  By 1930, a l a r g e s t o r e o f observations  data had been accumulated  (1,2) and e l e c t r o n p h y s i c s  had become a l e g i t i m a t e and f r u i t f u l branch  of s c i e n t i f i c  investigation. B a s i c a l l y , electron-atom interactions  can be c l a s s i f i e d  and e l e c t r o n - m o l e c u l e  i n t o f o u r general areas.  b r i e f d e s c r i p t i o n o f these i n t e r a c t i o n s i s given below.  A  •2  1.1  Electron  1.1.1  Impact  Elastic Collisions If  and  an e l e c t r o n  suffers  a collision  the net r e s u l t o f the c o l l i s i o n  of motion internal  o f the e l e c t r o n energy  elastic.  electron  o f the t a r g e t ,  suffers  kinetic  energy  is  less  i s a Coulomb  the nucleus orbital  the study that  o f the e l a s t i c  elastic  species.  strongly  The  theory  scattering  and t h e e x p e r i m e n t a l  takes electron,  One f a c t t h a t  scattering of electrons  s p a t i a l d i s t r i b u t i o n of the target's  direct  scattering  o f a m o l e c u l e ) , and t h e  the s c a t t e r i n g b e h a v i o u r , i s  of e l a s t i c  loss  energy.  the  (3,4)  t h i s energy  i n t e r a c t i o n between t h e i n c o m i n g  of the target  energy  reducing the i n i t i a l  Generally  1% o f t h e i n i t i a l  ( n u c l e i i n the case  electrons  and s i n c e t h e  some t r a n s l a t i o n a l  thus  mechanism by w h i c h  i s termed  i n the system  the target  o f the e l e c t r o n .  than  The place  the c o l l i s i o n  a d e f l e c t i o n , then to the t a r g e t ,  a target,  c a u s i n g a change i n t h e  then  o f the e l e c t r o n plus  must be i m p a r t e d  much  without  with  i s t o change t h e d i r e c t i o n  S i n c e momentum must be c o n s e r v e d  consisting  is  Processes  results  t e s t o f quantum m e c h a n i c a l  well  can o f t e n  worthwhile  d e p e n d e n t on  orbital  is fairly  makes  electrons. understood  be u s e d  wave f u n c t i o n s  as a  of the  target. Other elastic  important  scattering  applications  are i n the f i e l d s  o f the r e s u l t s o f  o f plasma p h y s i c s  and  3  radiation  chemistry.  electrons  tend  inelastic  collisions,  However  if  to  the  As w i l l  lose  most  electron  only  by  the  transfer.  in  systems  effect  be  significant  the  velocity  1.1.2  fact the is  that  of  known  very  1.1.3  lose  Inelastic  The  of,  for  collision  second  kind")  gains  of  of  first loss  can  momentum targets  this  alteration  of  electrons.  study  (often is  energy  given  the  name  d i s t i n g u i s h e d by  energy  in  in  the  the  collisions,  the  encounter  target. since  at  Little  they  are  experimentally,  or  their  all  or  of  of  for  all  this  collision  high  the  wherein  kinetic  dissociation  example,  producing  the  target.  Collisions  studied  inelastic  of  collisions,  reasons  density  group  Inelastic  ionization widely  to  the  energy  p r o d u c i n g an a  of  than  then  energetic  by u n d e r g o i n g  mechanism of  a high  superelastic  difficult  energy  less  target,  in  excitation  about  some  with  electron  of  below,  Collisions  type the  the  expense  the  is  aforementioned  Superelastic  "collision  of  d i s t r i b u t i o n of  This  their  energy  potential  can  of  discussed  producing excitation  excitation occur  be  of  the  electron  attention process  are  energy  to  target  have  collision many.  provides  p r o d u c i n g i o n beams  concentrations  of  energetic  electrons  cause been  the  most  phenomena.  Firstly,  a utilitarian in  excitation,  a mass  electronically  the method  spectrometer, excited  4  s p e c i e s i n atomic  and molecular beams and  i o n i z a t i o n i n i o n i z a t i o n vacuum gauges. mentioned above, the dominant energy  producing Secondly,  as  was  l o s s mechanism f o r  e n e r g e t i c e l e c t r o n s i s by i n e l a s t i c p r o c e s s e s .  Thus,  i n f o r m a t i o n on energy  l o s s cross s e c t i o n s i s necessary  f o r the understanding  of e l e c t r o n v e l o c i t y  encountered  i n such  areas as upper atmosphere r e s e a r c h ,  molecular plasmas and r a d i a t i o n chemistry. too, a knowledge of the e x c i t e d products inelastic  distributions  c o l l i s i o n s , and  Certainly  generated  by  the r e l a t i v e p r o b a b i l i t y of t h e i r  p r o d u c t i o n over a wide energy  range i s u s e f u l i n these  areas.  I n e l a s t i c c o l l i s i o n s w i l l be d i s c u s s e d i n g r e a t e r d e t a i l i n the next  1.1.4  chapter.  Electron The  one wherein  Capture final  type of e l e c t r o n c o l l i s i o n process i s  the i n c i d e n t e l e c t r o n i s captured by the t a r g e t  to form a negative i o n .  Information gained from s t u d i e s  of e l e c t r o n capture can o f t e n y i e l d values f o r e l e c t r o n affinities  and bond d i s s o c i a t i o n e n e r g i e s .  Further a p p l i -  c a t i o n s of such i n f o r m a t i o n occur again i n the areas upper atmosphere and r a d i a t i o n chemistry  research.  of The  formation of negative ions by c e r t a i n s p e c i e s can o f t e n have a s i g n i f i c a n t  e f f e c t on the c o n c e n t r a t i o n of f r e e  e l e c t r o n s i n a system.  E v e n t u a l l y i t i s hoped that the  r e s u l t s of s t u d i e s on negative ions w i l l have a p p l i c a t i o n  5  in  medical  underway on  research  to  assess  biological  1.2  Electron  studying  It  was  the  since effect  attempts of  are  organic  presently  negative  ions  systems.  Scavenging  In of  (5),  1963, the  known  Curran  results  at  the  (6)  of  time  suggested  some  that  an  ingenious  inelastic  electron  would  form  a  near  zero  energy.  SF  method  collisions.  negative  ion  6 (SF ") 6  has 0.05 and  by  been  capturing reported  eV,, that  of  zero  this  probability  of  the  and  in  species,  Curran The be  suggestion to  monitor  i f  is  the  the  electron  capture  occurs  with  was  mix  an  a  is  very  it  within  mechanism  importance detailed  in  would  of the  be  operative  high  next  of  (8)  in  upheld and  6  gas as  to  a  all  function  "scavenged" in  the in  the  by  target  SF^~ the  be  their  ion work  Compton e t .  scavenging  chapter.  SF ~  threshold  been  the  lost  c o u l d be  observed  has  electron  with  &  which had  and H e n g l e i n the  SF  current  inelastic  prediction  Jacobs  ion  encounter  each  increase  This (6),  at  the  to  Electrons  inelastic  Thus,  current.  only  energy  energy.  an  SF^.  that  of  (7).  electron  energy  electron  attachment  the studied,  an  technique  of  al. will  (9).  6  1.3  Instrumental  Methods  Instruments attachment an  processes  electron  energy,  a  action  1.3.1  and,  record  Electron  the  an  if  where  of  of  electron problem fairly  directly liberated  flux  are  usually  to  such  of  studied,  some a  by in  an  fashion  reasons  in  for  are  field. is  detailed  obtaining  order  not  this.  to  a  This  rhenium  surface,  electric  is  a beam,  or  electrons  this  have  in  any  monoenergetic.  temperature  cathode.  obtain  often  takes  filament  which  electrons  of  an  corresponding  (In  this  to  the  However,  to  electron  in  electrons  d i s t r i b u t i o n may b e  of  distorted  are  the  the  homogeneous  temperature  is  indirectly-  accelerated  The  a  thermionic  that or  an  This  energy. which  a Maxwel1-Boltzmann d i s t r i b u t i o n  energies fact  a  oxide  emitted  phenomena  that  tungsten  metallic  several  liberated  be  performing  employed.  the  energy  are  is  fact  electrons  heated  produced  There  of  a  metal  desired  the  of  from  analyzer  inter-  i o n i z a t i o n produced.  relatively  either  The  beam  from  source  form  heated  collision  beam w h i c h i s arises  emitter the  electron  high  controllable  Sources  A common p r o b l e m i n studies  of  electron-gas  energy to  and/or  components:  beam  the  Studies  inelastic  basic  electron  electron  amount  of  four  ionization is  the  Collision  study of  an  chamber  place,  description,  Electron  consist  collision  to  for  gun p r o d u c i n g  takes  device  in  the by  of  emitter. temperature  7  gradients  or surface  c a u s e d , when u s i n g voltage heated they  drop  they  Further distortion i s  directly-heated  c a t h o d e s , by t h e IR  a c r o s s the e m i t t i n g  oxide cathodes  eliminate  functions and  anomalies.)  are superior  the l a t t e r  (thus e n a b l i n g  problem  are o f t e n  unsuitable  and h a v e  Typically  distributions  innocuous  excitation with  regard to locating  elastic  1.3.2  or attachment  Electron  cross  much a t t e n t i o n  the t h r e s h o l d  follows.  gases. spread  from t h e r m i o n i c structure i n  particularly  energy  o f an i n -  process.  o f the d i f f i c u l t i e s  has b e e n d e v o t e d  monochromators.  some c u r r e n t l y  sample  sections,  an e l e c t r o n beam o f s a t i s f a c t o r i l y  review  c a n be  Monochromators  Because  recent  distributions)  they  spread can obscure d e t a i l e d  and i o n i z a t i o n  temperatures  h a v i n g an e n e r g y  b e t w e e n 0.5 and 1 eV., a r e e n c o u n t e r e d and t h i s  i n that  l o w e r work  at lower  f o r use i n t h a t  relatively  sources,  indirectly-  Maxwel1-Boltzmann  " p o i s o n e d " by even electron  to filaments  them t o e m i t  consequently with narrower  Although  area.  The e x i s t i n g  article  of obtaining  narrow  energy  to designing  p o p u l a r low e n e r g y  spread,  electron  designs are well  by K l e m p e r e r  directly  beam  covered i n a  (10).  A description of  electron  monochromators  8  The RPD Gun The retarding potential difference (RPD) gun  is an ingenious device for producing what has been called a "pseudo-monoenergetic" electron beam.  The prefix  "pseudo" i s added because the device i s not a true electron monochromator, but rather, i t i s capable of simulating the performance of a monoenergetic beam.  (In this thesis, the  term "monoenergetic" w i l l be used to describe an electron beam which has a true or simulated energy spread of the order of 0.1 eV., or l e s s .  Distributions w i l l be quoted on  a widely accepted d e f i n i t i o n of the energy width at h a l f the maximum electron current — FWHMJ. The RPD gun was invented by Fox, Hickam, Kjeldaas and Grove i n 1951 (11), and has been widely used for studies of i o n i z a t i o n e f f i c i e n c y by electron impact.(12). It has also found use i n the study of excitation processes (13). The device consists of several planar electrodes with rectangular s l i t s or c i r c u l a r holes interposed between the filament and the ionization chamber.  The s l i t nearest  to the filament (the draw-out electrode) i s operated at a positive potential with respect to the l a t t e r .  This serves  to draw electrons o f f the filament and to form them into a crude beam.  A second electrode (the retarding electrode)  is operated at a potential s u f f i c i e n t l y negative to cause the low energy portion of the Maxwel1-Boltzmann d i s t r i b u t i o n i  to be repelled and lost from the beam.  The resulting  9  truncated d i s t r i b u t i o n , having a sharp low-energy cutoff i s accelerated to the desired energy and proceeds to cause,> for example, a given ion current i n the ionization chamber.  A second reading is i n i t i a t e d with the  negative  potential on the retarding electrode changed by a small amount ( ~ 0 .1 V.).  1  This causes a s h i f t i n the position, of  the low-energy cutoff point. ion  The difference between the  currents generated i n this condition and the  initial  condition yields the i o n i z a t i o n caused by that band of electrons between the two  cutoff points, providing that  the p r o f i l e of the transmitted d i s t r i b u t i o n changes only in i t s low-energy cutoff point.  A magnetic f i e l d  parallel  to the beam d i r e c t i o n i s used to confine the electrons. There have been several theoretical papers published RPD  i n recent years which attempt to analyze the  method.  The  f i r s t , by Marmet (14), considers  the  phenomenon of space-charge-induced relaxation of the electron beam.  This phenomenon was  Hartwig and Ulmer i n 1963  t h e o r e t i c a l l y investigated by (15), and Marmet has applied some  of these authors' results to the RPD  gun.  Marmet's argument  is that in the area of the retarding electrode, where the energy of the electron beam is very low, the formation space-charge would be expected.  of  Hartwig and Ulmer predicted  that this would lead to a relaxation of the energy d i s t r i b u t i o n . That i s , rather than obtaining the desired beam with a sharp low-energy cutoff in the RPD  gun,  the d i s t r i b u t i o n would  10  symmetrize e i t h e r p a r t i a l l y  or t o t a l l y  to a Maxwellian.  With t h i s i n mind, Marmet was able to show, using s t r a i g h t forward a l g e b r a i c r e l a t i o n s , that the r e s u l t of studying any  e x c i t a t i o n f u n c t i o n using  the RPD technique would be  t o produce a curve c o n s i s t i n g of the sum o f the true excitation  f u n c t i o n and an u n s p e c i f i e d c o n t r i b u t i o n of the  curve's f i r s t if  derivative.  Dowell and Sharp (16) c l a i m  that  an RPD gun i s used to produce e l e c t r o n currents o f  greater Quite  than 10"^ A., such spurious  e f f e c t s are e v i d e n t .  probably the minimum current  necessary to d i s t o r t  curve shapes i s very  dependent on the geometry of the  p a r t i c u l a r RPD source being  used.  Another t h e o r e t i c a l a n a l y s i s o f the RPD source has been c a r r i e d out by the authors Anderson, Eggleton and Keesing  (17 - 1 9 ) . S p e c i f i c a l l y , they considered the  e f f i c i e n c y of transmission when a magnetic f i e l d theoretically  o f e l e c t r o n s through an  i s a p p l i e d to the beam.  aperture  They showed  that the energy p r o f i l e o f the truncated  d i s t r i b u t i o n can be markedly d i s t o r t e d during the beam through the gun.  I t should  the passage o f  be p o i n t e d  out that  this  d i s t o r t i o n i s i n no way r e l a t e d to that covered by Marmet (14), but  i s the r e s u l t o f the a c t i o n of the e l e c t r i c and magnetic  f i e l d s , and the presence o f apertures i n the gun e l e c t r o d e s .  of f i n i t e  It i s clearly illustrated  papers of Anderson, Eggleton and Keesing distortion  dimensions i n the  (17 - 19) that  can lead to f a l s e s t r u c t u r e i n RPD  curves.  this  11  Although on  the  the  negative  a  to  realize  it  fact  that  extremely  low  filtering  high  experiment. results  the  electron  has  devoted  of  using  an  of  of  adaptation its  valuable  record and  aforementioned a l . ,  the  choice  merely  technique source  underline  must  be  geometry  and  the  in  such  a way  much  can  where  IP  the  be  E is  beam  as  to  the that  thought  the  in  recent  curves  That  is  theoretically  remove  the  Morrison to  this  the  probability by  energy  a  of  electrons  of  causing  the  on of  in  particul  P of  method  is  as  ionization  of  P=p(E)  bombarding the  in  subject.  function: the  a  no  effect (20)  years  as  is,  employed  p h i l o s o p h y b e h i n d the  described  The  21).  operate  ionization potential  E<IP.  (20,  distribution.  careful  a  to  attempts efficiency  electron  is  Consider  E>IP,  data  idea  energy  Monochromators  ionization  The  follows.  for  The  dwelt  usefulness  examine  extremely  several  resolution  Basically  P=0  been  resolution  energy  is  to  Anderson et.  Electron  have  of  species  To use  has  technique.  their  Theoretical  source  these  an  the  have  conditions.  There use  paragraphs  subject,  only  been  and  in  two  disputed.  experimenters  careful  operating  to  has  Marmet  the  one  experimental of  of  be  cliche,  that  objections the  cannot  political  fruitful  previous  aspects  RPD m e t h o d  of  the  species.  for  electron,  and  Clearly  ionization will  have  a  12  distribution U  of  energies  is  the  energy  V is  the  accelerating  accelerating represented  of  emergence  voltage by  represented from the  voltage V,  the  I(V)  (21):  by  =  electron  applied  ion C  f(U)*f(E-V)  to  the  current, ? f(E-V)  I,  where  source  beam.  and  At  produced  p(E)  dE.,  an  is  where  IP  C  is  a  constant.  If  a  set  of  values  measurements  of  the  correspond  to  resolution  ionization  f(E-V) the  it  of  the  the  is  equation  very  however,  the  future. An  Winters,  to  true  curve  little  is  due  known to  the  the  at  (20)  of  f(E-V)  and  the  Both  of  theoretical  Courchene  equation  I(V)  a  low  is,  if  energy) for  has  p(E),  reviewed  expression.  ion  current  these  solution of  find  (these  function  each  this  The method s u g g e s t e d and m i g h t  the  expression  Morrison  the  from  if  measured  make  known  V (that  s o l u t i o n of  which  valid,  and  of  of  distribution difference solve  and  random n o i s e .  alternative  Collins  be  are  currents  curve)  solve  shape.  difficult. quite  to  methods  complications  is,  seek  possible  distorted  introduce  energy  be  ion  corresponding values  possible  practice,  I(V)  at  d i s t r i b u t i o n could  should  obtain  some In  known  electron  then to  is  efficiency  I(V)  by  factors  the Morrison  extensive  use  in  technique  d e v i s e d by  (21),  and known  as  (EDD)  technique  does  = C /  f(E-V)  p(E)  f(E-V)  to  the not  dE,  but  IP rather  takes  effective  advantage  energy  of  spread.  the  form of  Briefly,  consider  two  reduce  the  experimental  13  p o i n t s I ( V ) and  I(V ).  x  2  I ( V ) .- C /pfCE-Vj)  P(E) dE  X  I ( V ) * C j^£(E-V ) p(E) dE 2  Consider  2  I (Vj) - b I ( V )  4 I ( V ) , where b i s a constant  a  2  AI(V) Corresponding  «= C  / [ f C E - V j ) - b f ( E - V ) ] p(E) dE. 2  to A I(V) there i s t h i s new  distribution:  f(E-V) « fCE-Vj) - b f ( E - V ) . 2  The authors  showed that f o r Maxwellian  corresponds  to a c o n s i d e r a b l y narrower d i s t r i b u t i o n  the f(E-V£).  The v o l t a g e i n t e r v a l  parameter b are e m p i r i c a l l y  distributions,  (Vj - V ) 2  Af(E-V)  than  and the  chosen (with c e r t a i n  restrictions,  see r e f e r e n c e 21) and a p l o t o f Al(V) versus e l e c t r o n  energy  produces a curve corresponding to the i n i t i a l use of the narrower d i s t r i b u t i o n A f ( E - V ) ,  The authors have achieved  c o n s i d e r a b l e success with the method  Deflection  (21, 22).  Analyzers  D e f l e c t i o n a n a l y z e r s employ an e l e c t r o s t a t i c a magnetic f i e l d ,  or a combination  of the two to cause  s p a t i a l d i s p e r s i o n as a f u n c t i o n of e l e c t r o n energy initially energy filters  as energy  s i n c e they can be designed  thin slice to  inhomogeneous e l e c t r o n beam (10).  a n a l y z e r s may be used  of the i n c i d e n t  energy  field,  of an  This c l a s s of  monochromators or  to s e l e c t and transmit a distribution.  be considered i n the design of such  The  factors  a monochromator have  14  been outlined by Simpson  (23).  T r a d i t i o n a l l y , the greatest  problem has been to  design a monochromator which w i l l produce an electron beam of useable intensity (generally of the order of 10~ A.) while 8  maintaining an acceptable d i s t r i b u t i o n of usually less than 80mV., (FWHM)/  In order to get this combination of intensity  and resolution, i t i s necessary to operate these devices at low energies, but when this i s done, space-charge becomes a major factor to consider*  In Appendix I the theory behind  the  127° selector is reviewed, but a b r i e f description of the  two  currently popular selectors i s given below. The  180°  spherical e l e c t r o s t a t i c selector has been  used i n very sophisticated experiments designed to measure the energy losses of monoenergetic electrons of i n e l a s t i c scattering i n gases. workers using Simpson (23).  as a consequence  The two main groups of  this device are those of Lassettre  (24) and  The device consists of two concentric  hemispheres, to which i s applied a potential difference. Electrons radius  are deflected by this voltage difference, and the  of curvature of the electron trajectory i s energy-  dependent.  The spherical symmetry of the selector provides  for two-dimensional d i r e c t i o n a l focussing  of the beam. The  device i s capable of extremely high resolution (0.005 eV., has been reported but  with an electron current  at acceptable operating  of 3 x 10" A. (23)), 14  currents, the energy width of the  beam i s of the order of 40mV. (FWHM).  Constructional and  IS  operational mentioned  details  papers The  one  than  energy  filtered to  was  first  and  has  and  Kerwin  30),  the  127°  and  has  studies  of  selector  by  electron  It  in  of  in  the  previously  The  a potential  of  beam  widely  and  ionization  electron  impact  produces  electron  is  The  by  device  Clarke  r e f i n e d by  used  the  difference  electrodes.  monochromator  from  cylindrical  electron  investigated been  differs  possessing  cylindrical  extensively  monochromator -  virtue  focussed  an  (26).  covered  selector  symmetry.  concentric  been  (27  by  and  as  well  24).  spherical  used  been  electrostatic  above  rather  applied  (23,  127°  discussed  have  as  an  curves  (31).  currents  Marmet  electron  efficiency  excitation  (25),  of  Typically,  between  10"  7 and  10  A.,  slightly  1.3.3  with  inferior  Mass  in  order  negative  necessary the  ions  to  the  to by  have  been  Three extensively  used  been  used  and  Clarke  by  (25)  study  a mass The  types in  the  of  mV., which i s the  180°  only  selector.  impact,  Frost among  both  positive  usually  spectrometer  of  some  mass  by  types  of  Farmer  mass  with  others.  This  description  spectrometers  have  been  monoenergetic  magnetic-focussing  and M c D o w e l l  considered  (33).  spectrometers  conjunction The  of is  various  of  formation it  reviewed  experiments.  has  performance  electron  include  experiment.  available  impact  to  50-70  Spectrometers In  and  a d i s t r i b u t i o n of  (34), type  mass  Brion of  electron spectrometer  (28,  mass  32),  16  spectrometer although  is  it  quite  requires  that  electronics  be  to  ground.  This  of  high  energies.  ion  operated  the  magnetic  the  requirement  introduces  For  field-free from  the  electron and  is  mass  the  ion  principle  periodic  pulse.  A l l ions  a  mass  gating the  instrument Hamill  (35)  has  space  is  techniques  monitoring  its  of  of  and by  the  this fringe  a single  to  a  the  peak  successfully Collin  and  (36),  the  focussing  has  the  depend ions  shielding  successful. achieved  instrument.  This  ion to  energy the  separate,  chosen  masses.  time.  the  permit  This  e m p l o y e d by M e l t o n using  and  Special  equipment peaks.  a  same  to  detection  both  as  their  of  some  device  on  function  or  field  magnetic  accelerated  as  a  monochromator,  that  the  s h o u l d be  alter  partially  which  often  magnetic  elaborate  applying  Firstly,  ionization  chamber  electron  allows  applied  the  need  selector,  voltages  into  filtering  are  recorded  been  satisfy  drastically  only  velocities  drift  spectrum  the  time-of-flight  the  A field-free  fields  spectrometer  on  and h a v e  respect  electron  accelerating  can  are  operates  energy,  to  with  difficulties.  necessitates  Another  is  associated  many  deflection  which o f t e n  popularity  potential  the  presents  destroy  This  and  RPD g u n ,  an  magnet a  an  with  Secondly,  in  partially  procedures  itself  a high  electrical  analyzing  with  When u s e d  high  volume.  properties.  gun  use  optimum p e r f o r m a n c e ,  orbits  can  for  requirement  instrument of  the  at  latter  fringing  chamber.  suitable  and  RPD m e t h o d .  17  time-of-flight  The  suited  to  wherein pulse ion  this  the  more, and  the  while for  multiple of  a  gas  in  popular  monoenergetic conceived  (37,  38)  a  be  in case  mission latter near the  and  the  ion  of  the  field  the and  McGowan  the  the  Furtherof  ions,,  The use  energy  for  radio-frequency  The  These  III,  but  of  ion  minimizes Clarke  these  ions  (5-50  (41)  employ  having, a of  different trans-  eV.). to  penetration have  (39)  instruments  a high  monochromator field  Zahn  they  possessing  energies  electron  von  electrodes  separate  suited  co-workers  basically,  up b e t w e e n to  of  have  instruments  a n d by  theory  the  mass  are  and h i s  of  scale.  and w h i c h  Paul  the  simultaneous  necessary  work.  in  most  work.  sample.  quadrupole,  and  is  years,  by  low  region  This  impact  energy  which  advantages only  on.  ion  monopole,  arrangement  the  potential  set  the  the  impact  Chapter  permits  chamber.  few  monopole.  in  have  and  operation  transmission  similar  developed  case  is  electron  very  of  field-free  enable and  mode  considered  the  last  requiring  feature  ground  two  geometric  They  of  a  high  gas  usually  electron  outlined  particular  very  quadrupole  and  the of  a  particularly  during  electron  techniques  the  radio-frequency  masses.  beam  are  become  will  electron  is  the  the  the  calibrating  spectrometers,  in  of  determination  were  withheld  monoenergetic  There  to  is  creation  has  is  The p u l s e d  the  gating  calibrating  precise  beam  instrument  detection a  electron  chamber  spectrometer  application.  facilitates  important  mass  The  operate into  successfully  i  used a quadrupole mass f i l t e r i n conjunction with a 127° electron selector.  1.4  Experimental Objectives and Studies The object of this work was to construct an  instrument which would permit the study of a variety of i n e l a s t i c and electron attachment  phenomena using mono-  energetic e l e c t r o n beams. The basic part of the instrument was chosen to be the 127° electron velocity selector.  This choice was  based on the considerations that i t i s a r e l a t i v e l y easy device to construct and modify, the current/distribution behaviour was adequate for the proposed experiments, and furthermore, workers i n the laboratory were already familiar with the behaviour and some of the operational problems associated with i t (28, 32). Two very similar instruments evolved during the course of this work.  Both featured 127° selectors and  i d e n t i c a l 127° analyzers to study electron energy  losses,  Paul-type mass spectrometers, and specially designed collision  chambers to f a c i l i t a t e the accurate recording  of ionization e f f i c i e n c y curves.  The instruments w i l l  be discussed i n Chapter I I I . The studies which were made are l i s t e d and categorized i n Table I.  Table  Summary  INELASTIC  of  SCATTERING  Helium Ethylene  Studies  I  Performed.  POSITIVE  IONIZATION  Helium Nitrogen Oxygen  NEGATIVE  o-/o  IONIZATION  SCAVENGING  Helium  2  O'/CO  H y d r o g en  O-/N O  Xenon  2  Br"/Br  2  ci'-/cci S  F  6  " / S F  4  6  I"/CH I 3  Br"/CH Br 3  CI-/CH3CI  Carbon  Dioxide  Carbon  Oxysulfide  Carbon  Disulfide  CHAPTER  II  THEORETICAL  result with in  of  an  the  The  basic  the  interaction  atomic previous  directly  to  excitation inelastic  and  covered  scavenging inelastic processes,  a  In  target  order  this  chapter,  is  in  unique,  relating  to  fact  scattering the  to  and  in  from  this  by  this  will  of  electron of  procedure  A brief given.  be  the  electron  technique  be  and  processes  application  this  first  capture  Although  chapter.  will  of  theory  non-dissociative  by  acts  discussion  presented.  gained  theory  the  these  sequential  discrete  the  electron of  relate  and m o l e c u l e s as  the  summarized  which the  as  electron  been  are  well  the  accordingly,  discussion collision  be  a  results and  some  facilitate  results  have  atoms  as  place  energetic  thesis  collisions,  to  take  The p r o c e s s e s  i o n i z a t i o n of  this  can  free  and n o n - d i s s o c i a t i v e  experimental  general  in  observations in  separate  the  electron  molecules. previous  molecular  work  which  of  chapter.  the  dissociative  rather  or  processes  the capture are  warrants resume"  of  21  2.1  General  Collision The  el ect  Theory  objectives  ron-atom  or  If  a  collision  theoretical to  the  treatment  a) be  elastically  electron  electron  what  a  of  this  is  the  as is  a  the  then  a  information relating  electron  fraction  angular function  the  change  beam  will  as  function  distribution of  a  of  the  the  incident  energy?  of  exciting  discrete  probability  the  d e p e n d on what  is  angular  states  as  distribution  electrons,  the the  state  a  function  of  energy?  in  the  site?  case of  the  and does  probability  of  of  or  this  exciting  dissociation  ionization,  two  of  excited?  (ionization and/or  distribution  collision  is  scattered  states  g)  the  what  ally  function  energy  supply  entering  energy?  f)  as  considered,  v i b r a t i o n a l and e l e c t r o n i c  distribution  continuum  electrons  be  scattered?  what  e) in elastic  is  can  of  energy?  d)  of  fraction  electrons  rotational,  chamber  treatment  collisions  monoenergetic  should  how d o e s  c) scattered  theoretical  questions;  what  b) of  a beam o f  following  any  electron-molecule  enumerated. gas-filled  of  more  what  is  electrons  continua)  the leaving  22  h)  what  attachment, negative  the  is  result  treat  based an  the  exact  any  perhaps, and  it  stages  many  approximate  type  of  mention  the  of  electron formation  As w i l l  be  treatment  necessary the  of  a  atom to  approximate  applied  the  incident  about  100  eV.).  treatments  are  valid  necessary  to  calculation discussed  inelastic  electron Some  achieve  an  Since  this  concerned  with  energies,  present  The  work  is  the  for  low  to  scattering  can  be  is  been  yield  the  essential are  the  less  sophisticated but  often  the  makes  These  sophistication the  points  are  by  Gerjuoy  thesis  is  entirely  measurements  at  low  this  the  problems  theories  involved  in  (42).  electron  do n o t  experimental  illustrated  to  invalid  article  compare  theoretical  can  (typically  more  quantum m e c h a n i c a l  which  is  approximations  methods  energies,  survey  to  be  scattering  There have  it  difficult.  experimental  with  electron  c o l l i s i o n s where  extension  excellent the  of  lower  prohibitively  in  standard  to  at  below,  d e v e l o p e d which  these  are  discussed  resort  but  attempt must  scattering)  that  of  would  particles  of  calculations.  methods  most  which  microscopic  electron-H  is of  theory  above,  of  electron  is  information listed  they  energy  a  complete  interaction  for,  various  than  which  quantum m e c h a n i c a l  impossible,  when  of  on q u a n t u m m e c h a n i c s .  (except  at  p r o b a b i l i t y of  ion? Clearly,  to  the  offer  results.  treating  satisfactorily  by  23  considering obvious  electron-H  starting  independent of  the  point  [V  V  1  (and  integral  the  equation  • LT  2  2  l  .  2  * = 0  r  12  Planck's  E  =  sum o f t h e e n e r g i e s of the incident e l e c t r o n and the g r o u n d s t a t e energy of the hydrogen atom,  e  =  electronic  =  distance  12  s  s  »  e  P  a  mass  r  a  total  the  is  and  =  of  of  n  summation  t  hydrogen  incident  applies  atom  n  (  and  nucleus, atomic  function  eigenfunctions of  electrons,  system.  a product  the  of  in  the  incident  is: r  i  ) ,  discrete i|»  n  states,  represent  eigenfunctions., wave  the  the  function  to  states.  of  ¥ as  That x  n from  incident  e  state  wave  2  electron  n  write  * (r )  continuum  2  electron,  function  to  the  n  2  electron °f  n  electron. ( W)  d /dz )  charge,  known s t a t i o n a r y  atom  to  of  wave  procedure  the  2  constant,  i °  t  2  +  si ) ]  *  2  d /dy  bound  is:  + Sr  the  h  n  +  and  time-  consisting  rest  unperturbed of  2  1)  system  the  =  * the  2  2  scattered)  where  • 8JL5»(E  the  is  m  normal  hydrogen  2  theory  The  (d /dx  H  of  for  (labelled The  h  quantum  44).  =  r  terms  2).  (43,  V  r  The  any  2  •  2  scattering  equation  electron  (labelled  where  for  Schrbdinger  incident  electron  atom  and  the  x  and  the D  ( i) r  elastically  the  ordinary is  the  sum  scattered  24  wave,  and  the  resulting Using of  product  the  It  i^ . n  the  *  is in  n  order  to  functions,  yield and  the  of  Born  only  in  resulting  expression form  Specifically,  the  target  wave  That  electron  wave  incident  wave,  hydrogen  atom.  solved  to  any  is,  recast  function and  the  Using  yield  approximation kinetic  function  energy  is  the  the  interaction fails  below  100  to  eV.  and  to wave  with  agree  electron the  with  at  be  for  solved wave  this  stage.  of  interacts  the  describe  only is  target,  any can  be  free the  function the  is involves  therefore  <p  of  Q  equation  behaviour,  satisfactory  incoming  equation  interaction  substitution,  scattering  energy  Approximation usually  this  state  functions  wave  product  used  the  approximations  the  the  normally  logically  of  '¥ as  that  desired  electron  to  to  approximation  system  due  ground  the  properties  the  cannot  made  the  state.  behaviour.  the  be  known o f  minimally with its  of  must  incident  in  a way  scattering  nth  possible  the  approximations  (44).  is  such  the  known  o f * and  the  correct  widely  the it  in  waves  excite  terms  the  ignored.  to  using  that  change  be  the  to  functions,  resulting  most  assumption  and  solve  derive  the  The that  to  represent  n  equation  expressed to  *  scattering  wave  necessary  Unfortunately, exactly  atom  are  the  function  SchrBdinger  functions  of  inelastic  hydrogen  rewrite *  from  this  the  remainder  can  However, when  large and  experimental  the  this  the compared  thus  the  results  Born  25  Even where  the  for  target  the  wave  scattering  behaviour  techniques  permit  for  some  atoms,  aspects  and  for  themselves  simple  functions cannot  very of  case  be  are  the  approximations,  atom  known e x a c t l y ,  this  the  (although  (42)).  target  and  hydrogen  calculations  behaviour  molecules,  the  predicted  accurate  this  of  to  For  wave  modern  be  made  more  complex  functions  introduces  are  further  complications. Since have,  at  work,  the  of  this  (44)  recent  and to  review  presenting  be  will  not  useful  can  be  section  relevance  further  Some  summarized  of and  M o i s e i w i t s c h and  remainder  of  this  or  interpreting  the  chapter  present  the  modern  referred  be  to  in  (45).  devoted  to  gained  sources,  experimental  and  more  Smith  will  present A summary  knowledge,  experimental the  the  from Mott  by  developing  to  calculations  developed.  obtained  (43),  problem are  theoretical  in  be  cross  article  and  either  direct  from McDaniel  the  The  from  little  approximations  approaches a  time,  subject  higher  Massey  quantum m e c h a n i c a l  which  results  of  will this  work.  2.2  Electron  Impact  An impact and  general  excellent  excitation  Burhop  Excitation  (46).  cross  summary  of  the  behaviour  sections  has  been  They p r e s e n t e d  six  observations  applicability.  This  summary  is  given  of by  reproduced  electron Massey of  fairly  verbatim  26  as  follows  (47): "a)  than  the  cross  - 1  sections  log not  as  E"*.  For  involving  change  electron  allowed  is  which, of  while  of  E.  For  fall  is  optically  multiplicity, rapid  for  '  inelastic  energy  rate  greater  the  as  forbidden  decrease  is  transitions  multiplicity. sections  multiplicity  At  this  much  all  electron  much m o r e  Cross  "c)  very  excitation,  with  change  of  energies  exchange  off  very  change  of  the  transitions,  any  is  »b)  energies  transitions  involve It  for  fall  allowed  E.  do  electron  threshold  optically E  At  in  are  only  a narrow  electron  negligible,  transitions  for  are  transitions large,  range  energies  the  cross  involving  if  at  a l l ,  close  to  threshold.  for  which  sections  considerably  electron  for  larger  at  optically  than  for  others. "d) concerning in  which  some  the  electron  of  the  that  strongest  unimportant, very  In the  "f)  is  sections  excitations  the  this  with  available the  but  energy there  i n which there of  the  atomic  is  range  is no  electron  case.  energy  angular  in  important,  quantum number  in  steeply  information is  cross  exchange  azimuthal  " e)  falls  definite  relative  indication  change are  Less  range  i n which  d i s t r i b u t i o n of increasing  When e x c h a n g e  is  exchange  scattered  is electrons  angle.  predominant,  the  angular  27  distribution  is  The concern for as  the  a  of  good  of  (usually  ground)  and  can  be  would  it  apply at  excitation valid,  to  to  be  process, as  when  the  square  Born  by  to  the  the  of  the  optical to  this  Approximation  selection  electron  the  state  initial  selection  rules  impact.  threshold  Approximation is  above,  is  discrete  Since  the  by  a  the  optical  near  shown  proportional  initiated  Born  to  state.  the  transitions  been  to  work  sections  Approximation  similarly  energies  indicated  has  involving  valid,  the  It  proportional  that  excitations  electron  and,  is  present  cross  section  excited  follows  considered  However,  the  the  forbidden  Born  element  probability  then  the  cross  approximation  to  excitation  energy.  excitation  matrix  relevance  optically  where  dipole  quantity,  the  and  electric  transition  of  electron that  the  uniform."  points  allowed  (48),  applicable, to  more  behaviour  function  Lassettre  is  main  optically a  much  not  of  at  rules  an  all change  drastically. One so-called In the  this  exchange  process,  target,  ejected. rigorous  reason  and  This  this  low  energy  behaviour  scattering  can  become  very  the one  for  incident  electron  is  of  the  previously  permits  the  violation  of  the  rule  0,  commonly  optical  selection  the  p r o h i b i t i o n of  the  observation  of,  AS =  intercombinations e.g.,  by  electrons  is  normally  selection  singlet-triplet  that  important.  captured  bound  is  called  rule.  transitions  Thus, at  28  low  impact  energies In  inelastic points  listed  in  helium  of  employed authors state  respect  and  same  found  no  exchange  the  (50)  the  allowed  in and  the  the two  Raff  the  at  0°.  to  at  very  The  publication  2 p 1  large  the  and  groups  and h e n c e  of  the  by  workers  former  of  is  Raff,  the  2^S of  the  2 S 3  The  with  in  is  spectra  by  Kuppermann and  the  The that  was of  dominant  difference Kuppermann  scattered to  workers  the  other  excitation  latter  in  the  by  excitation  respect  other  excited  on  the  ine1 a s t i c a l l y  the  on  excellent  (49)  eV.),  explained  angles  while  detail  be  the  spin-forbidden with  of  state.  the  p u b l i s h e d on  excitation  intensity  can  differences  (51).  is  (50  since  An  S i m p s o n and M i e l c z a r e k .  beam,  greater  the  state,  the  observing  incident  somewhat  of  for  both  on  mind  dependent  results  Kuppermann and  experiments  were  electrons of  work  energy  intensity  the  in  Although  in  summary,  experiment. the  results  keep  strongly  in  state  ground  equal  peak  is  the  .  (This  approximately optically  in  evidence  that  Burhop's  to  S i m p s o n and M i e l c z a r e k  scattering.)  found  and  incident  1*S  phenomenon.  important  contained by  helium. to  is  obtained  Raff  the  in  hand,  is  scattering  Kuppermann  it  employed  this  common  published experimental  Massey  spectrum  conditions  example  a  examining  scattering,  excitation the  is  were  the  direction  were  observing  discussed  Raff  in  a  in  subsequent  29  Similarly, in  an  electron  e nergy  of  impact  the  reference  nitrogen  and  15,7  In  different  on  can  study  wide  and  flexible  states  the  and  similar of  the  of in  to  that  can  be  Electron  performed  be  possible result  seen  in  Heideman, incident  instrument  inelastic range  in  of  at  changes  of  changing  Fig.  Kuyatt  3  showed  the  of  and C h a m b e r l a i n ,  energies  from  electron  of  35  eV.,  remarkably  previous  the  moment  are  atoms  molecules.  opposite (53)  made  from  conjunction used  should  by  profitably  potassium a  Simpson  increase  of the  while  important  are  chosen  the  latter  Recently,  on  vapour  the by  inelastic  employing  say  that  a  a  combination  range  of  substances  studied.  in  the  general  great field  deal of  of  research  electron  an  apparatus  Ionization  To  of  former  for  desired.  the  a  optically  employed  Such  have  determination  scattering  (23).  most  For  measurements  with  greatly  valid, is  can  location  conditions  situation  have  the  The the  and  and  discussion  scattering  applications.  experimental  Impact  the  strengths  electrons  beam  techniques  which  2.3  the  Ross  scattering atomic  the  Born A p p r o x i m a t i o n i s  application Hertel  of  oscillator  application, that  of  gathered  applications  forbidden  so  same  be  the  optical  work  can  run with  the  that  these  beam  as  the  profiles. It  of  of  spectrum  this  spectra,  eV.,  example  incident  52,  two  an  has  impact  been induced  30  positive As  an  ion  formation  example,  a  quick  Spectral  Data"  Institute  would give  that in  this  the in  has  been work  the  this  the  positive  shapes  ionization  use  one  spread). main  the  chapter  to  When t h i s  vibrational  difficult  for  the  electrons  and  given  was  to  to  by  the  rapid  photoelectron the  need  such  (57  the  the  in  curves and  and  shapes to  use  a  measurements  to  in  ions  using  classify  has by  the energy  of  the  the  For  information  at  (55).  of  one  successful 59)  of  electron  ions . (56).  to  Franklin  1964,  available  -  concerning  described  of  studies  field  and  spectroscopic  were  ion  alternatively  such  extremely  spectroscopy for  of  optical  which  and  on  data  confined  general  positive  (57)  be  necessary  locate  of  threshold,  Field  (or  states  elsewhere  the  by  effect  of  Petroleum  volume  will  initiated  study  Mass  positive  the  the  is  of  efficiency  techniques  discussed  then,  it  the  was  Since  of  understatement.  information  information  electronic  obtain  to  electrons  work  methods  obviated  been  reduce  the  the  section  curves,  photoionization  of  this  detailed  of  of  close  gross  American  further  summary  has  the  idea  a  "Catalog  ionization  fairly in  make  the  aim  some  deconvolution  incentives  are  The  some  monoenergetic  monoenergetic  which  of  efficiency  of  previous  get  at  partial  gain  region  ionization  of  a  An e x c e l l e n t  To  source  to  to  p u b l i s h e d by  discussion  area.  glance  collected.  energy  t h u s ,  (54)  was  detailed  w o u l d be  reasons was  and that  time.  development  largely electron  impact.  31  The the  nature  of  ionization, in  the  the  the  overall  probabilities A discussion  2.3.1  information  threshold  influence  some  of  Threshold  Laws  for  What threshold  law  is is  a  the  increasing  electron  a  amenable cross be  taken  of  to by  certain  answer  can  occur  1(E)  is  the  (E-IP),and  the  should  an  current  the  the  the  assumptions  to  a power ion n is It of  unique  law.  current the is  as  a  exponent expected  is,  ion.  function to that  be  and  normally  of  statement  can  within  the  below,  an  normally  of  the  n should  for,  single  n  ,  differ  double,  ionization  absolute  be  solved  unequivocal expected where energy  theory  or  depending  etc.) to  not  framework  excess by  From  more  should  problem  is  of  threshold.  relatively  determined  (single,  ionization  function  I (E) « ( E - 1 P )  ionization e.g.,  the  a  is  but  answer  That  of  relationship as  discussed  This  states  calculation  This  treatment,  obtained.  transition  ionization  threshold  be  autoionization  impact  a small  ionization. that  impact  follows.  problem  is  involves  Ionization  over  this  of  the  applicable  above  sought  electron  electron  ion  than  and  points  theoretical  degree be  range  for  imply  experiment. on  in  energy  treatment  be  as  as  for  various  Direct  viewpoint,  sections  exactly  to  to  increase  energy  theoretical  to  generally  describing  unspecified  process,  these  sought  currently  prevalence  transitions  of  is  law(s)  and  ionization for  which  but a  single  32  state a  for  any  threshold  might  vary  bound  is  law.  depending  for  has  E<IP).  The  in  do  not  long-range  col l i s i o n single  particles  are  interacting considers is  which  two  of  of  product  impossible  and  The the  to  threshold  detailed  particles  species,  features  law.  produced  behaviour.  In these  ion,  It in  electron product  mutually  the  particles,  an  solution  because  the  exact  specify.  of  Although  of  which  lower  threshold  a positive  forces.  The  derivation  the  the  defining  bounds  difficult  (60).  neutral  electrons  Coulomb  the  affect  determine  ionization  via  the  interaction  lower  in  potential,  bound i s  Wigner  that  studied.  upper  by  itself  clear and  ionization  mentioned  the  theory  three-body  only  of  the  nature  of  system. The  will  be  have  law  produced  1.5  for  little  or  no  field  more  nearly  evolved be  is a  have  indeed  a power  variety  have  to  which  correct. been  unwise  of  to  law  It the  treatment  attempt  to  (n)  the  the  very cover  (which  that  ranging that  from  there  1.0 is  theoreticians problem  theories  is  in  great  in  the  which  sophisticated them  the  but  n  various of  problem  indicated  appears  sure,  necessarily  the  (I(E)«(E-IP) ),  exponents  among  To be  of  generally  ionization.  consensus  as  treatments  below)  single  this  would  theoretical  reviewed  threshold  to  the  species  been  is  the  the  is  upper  point  collision  problem  have  important  the  impact  on  It  The  of  the  species.  E should  p r o v i d e d by  (I(E)=0  laws  neutral  and  have it  detail  33  here.  Rather,  approach  used It  the  three  solution  a by  was  of  been  Approximation w i l l  at  energies  low  shown  how  However,  prediction  the  that  as  of  Geltman it  a  e lect  an  free  ron  threshold  two  electron.  a  wherein the is  other  cross  by  of  law:  plane  I (E) « ( E - I P ) latter  idea,  (60)  to  that  is  3  the /  2  that  poor  has problem.  electrons, feel  the  nucleus, must  be  used  nucleus)  by  one  a  than by  (62,  Coulomb  escaping  produces  electron  63)  alternate  the  (64). one  full  those  approach  An  but  and  rather  (i.e.,  this  Both  field,  described  wave  even  this  I(E)«(E-IP).  is  the  considered,  the  target  the  (61)  electrons  the  of exact  law,  answers.  functions  is  of  F u n d a m i n s k y and Massey  electron a  are  a Coulomb  This  the  sections  applied  the  wave  threshold one  that  Geltman  emergent  u n i n f l u e n c e d by  law: The  Bates,  but  repulsion of  in  interactions  Wigner  different  their  given.  threshold  62).  of  impossible.  interactions  charge  electron  and by  produces  and  the  positive  to  (61)  treatment wave  ref.  two  be  methods  ignoring certain  a valid  mutual  consequence,  appropriate those  the  that  the  a  produces  ignore  considers of  of  absolute  also  the  known,  Born Approximation i s  approximation  effect  (see  that  are  basic  will  c l a i m e d by  d e p e n d i n g on what  treatments  workers  give  of  the  problem is  consist  has  of  above  scattering  It  the  and  various  particles  methods  though  outline  mentioned  this  interactions.  one  the  emergent  Approximate  Born  general  might  not  34  experience seems,  at  pointed the  the  full  first  out  by  electrons  Coulombic force  sight, Temkin,  were  to  directions  and w i t h  they  certainly  would  However,  if  the  velocities,  then  law  apply,  would  be  Rudge  and  Bhatia escape  In  whereas  There  (66)  been  employing a  which  an  asymptotic  threshold be  that  on  the  the  of  law  for  of idea  of  the  Significantly, three-body  of  of  that  the  this  that  this  by  classical  mechanics.  as  opposed  quantum  his  to  different  case,  a  nucleus.  threshold  the  exponent  mechanical particular,  linear (67)  threshold  method  treatments  of  the  i o n i z a t i o n must treatment, detailed threshold  to  take  into  could  law,  often  of  occurs  and  is  important.  and be  the he  described  employing in  of that  account  adequately  possibility  relied  mechanism  particles  (68),  certainly  Wannier  p o s t - c o l l i s i o n motion,  mechanics  the  linear  In  then  Peterkop  departing  (The  opposite  by  the  problem  if  given  the  attempted  demonstrated  to  In  (60)  Wannier  nature  impact  the  quantum  function  elegant  immaterial  interaction  other  in  shield  the  performed.  wave  (69),  would  second  been  that  core  quite  case,  nucleus  has  (65)  with  with  the  velocities,  controversial  most  Wigner  equal  calculated  electron  Wannier  c o l l i s i o n is  only  the  the are  have  ion  directly  first  in  by  One  the  electron  the  dependence uses  from  by It  Sullivan  escaped  inner  which have  Seaton  and  interact  l<nil.5.  calculations  unrealistic.  approximately  the  escapee.  n  be  electrons  outermost would  to  exerted  systems  classical where  35  one  is  With  dealing  this  in  analysis the  of  three  to  orbits  motion  To  be  on  the  proceeded  object of  the  of  large  distances  to  (the 180°) of  and  the  those  electron  only  those  conditions  above  will  lead  to  electron  derive orbit  so  behaviour.  it  possible,  of  the  in  a  the  The  of  was  found  move  velocities. which  tend  which have  must  this  find  the  rate  of  function  of  I(E)«(E-IP) •  1  been  reviewed  extended  by  Vinkalns  treatment  of  the  The that  authors  due  most  to  considering considered  recent  Temkin,  approached  the  discrete were  and  2  7  Bhatia problem  .  Wannier's  and in  bound s t a t e s  certain  threshold  so-called  Sullivan a in  made mechanics  law  which  method  and  (65).  Gaylitis law  These by  states  "doubly-excited"  was  has  threshold  The  of  increasing  unique manner, H".  placed  increase  be:  1  the  constraint  found  is  yielded  be  correct  energy.  recently  Wannier  statistical  This  emerge  asymptotically  the  a  in  equal  of  as  the  directions  consideration  orbits  those  their  electron to  that  this  favourable  would  that  of  to  to  which  ionization.  would  of  was  form  i o n i z a t i o n problem,  number  it  orbits  orbits  constraints  that  analysis  which to  interaction  nucleus,  with  zone,  on  the  (70)).  classical  properties  between  move  particles  the  It  from  angle  a  this  (ionization).  reaction  went  to  electron  i o n i z a t i o n have  precise,  asymptotic  the  to  tends  more  an  The  directions  of  then  at  between  Hamiltonian describing  escape  leading  the  Wannier  properties  double  opposite  to  the  the  electrons,  from  mind,  Coulomb f o r c e s  particles.  determine lead  with  (71).  36  states  of  in  bound  of  wave  the  negative  excited  states.  functions  to  function  describes  they  circulating  are  nucleus. being and  A second  case,  second  the  different. both  wave  states lower of  where  where  are  where  the  equivalent  ionization such  result  that  the  incomplete, would 1.25.  the  ionization  lead  -  a  the to  was  a  when  are  ) /  2  ,  are  threshold  An a l t e r n a t e  electron  the  nucleus  orbits  are  significantly  were  the  latter  derived  that,  in  using  general, have  there  a  number  are  reversed is  and  the  region, is  of  of  of  how  and  the  exponent  authors  the  form:  which  showed  are  0<a<l/2.  between arises  number  extrapolating  the  that  at  the  calculations  confident  work  states  govern  energy,  their  Wannier's emerge  number  might  higher  possibility,  similar  electrons  assumption  law  certain  known f r o m  two  then  law  by  the  separated  ionization  authors  one  from  spatially  the  Although  where  in  found  it  threshold  wave  is,  is  an  One  That  preferred  From  types  distance  caused  system  are  increasesat  into  3  it  Since  behaviour.  I ( E ) oc ( E - I P ) (  the  distances,  orbits  states  this  of  same  are  two  states  describes  field  situation  occurs  proposed  in  the  electron  electrons  situation.  electron.  electrons  preferred.  similar  the  Nevertheless,  ionization  roughly  of  the  authors  function  and  two  electrons  dipole  the  functions,  states  that  a  which  roughly  Eigenvalues  energies.  orbits  at  wave  of  The  two  (inner)  radii  in  describe  the  i n f l u e n c e d by  the  ion,  1.5 from  This and a  37  different  assumption  states  that  is  The where  there  the  due by  is  are  to  one  modified the  show the by  (88).  and  an  that  more to  extremely  statistical is  his  theoretical  be  2.3.2  Classical It  would  sections  of  describing energy  produce  general the  range  previously  to  that  unsatisfactory  greater  than  of  these  above  threshold.  quantum  mechanical  at  low  energies  Wannier to  claimed  single 2.  to that  ionization,  In  general,  ionization  n  n  be  cross It  Cross  any  electron  impact  capable sections has  Sections  theory  been  calculations  (Born  Coulomb-  (E-IP ) .  that  must  given  derived  nrfold  Ionization  accurate  of  for  to  axiomatic  usefulness  behaviour  just  of  proportional  perhaps,  he  treatment  law  and  law  proportional  although  threshold  Calculations  is,  attempt  excess,  his  argument  similarly  slightly  the  approximately  of  ionization.  to  will  extension  double  analogy  that  explanation  for  law  However,  threshold  ionization  energy  expected  the  single  the  is  an  log(E/IP).  2  is  theoretically.  qualitative  simple  be  electrons  of  of  ionization  of  threshold  might  higher  derivation  of  exponent  3  or  treat  number  I (E)« (E/IP) /  emerging  Geltman used  2  increasing  is:  double  one  treatment  the  the  law  square  the it  (61)  I(E)*(E-IP)  employed  or  quantitative  Born  law:  three  of  difficult  Geltman  Wannier  threshold  treatment  understandably there  regarding  which cross  of in  the  mentioned either  Approximation  are  38  calculations) (higher been  a  or  are  approximations resurgence  calculations  (72),  of  The  success.  are  relevant  explicit of  to  threshold  a  Thomson  the  of  energy  electron  is  velocity  between  given  to  lead  there  has  classical  with  a  fair  classical is  degree  calculations  that  sections  as  to  use  their  the  made in  the  notation single  by of  is  they a  provide  function as  general  p r o b l e m and  and  the  suffers  and  initial and  a  that  it  than  the  target.  The  is  the  is under  atomic  relative  electrons of  (72),  given  of  from u s i n g  that  the  velocity  from  laws  greater  target  Bartky  the  conditions  (aside  that  an  thereby  the  place)  thus,  ionization  in  the  is  theory  first  incoming  Bauer  it  showed  determine  derived  as  electron,  electron  the  that  that  target,  transferred  in  the  the  is  Thomson a p p l i e d  to  energy of  theory  argument  it. the  stationary,  solely  for  by:  cross  orbital  simple matter  mechanics  determined  an  momentum t o  amount  classical  section  met  thesis  classical  with  approximation  the  the  approaches  mechanics  binding  Using  this  The b a s i c  collision  relatively  main  for  simplest  electron  c l as s i c a l  the  in  certain  these  which might  (73).  transferring  which  work  in have  that  perform  laws.  impinging  a  these  to  Consequently  interest  reason the  difficult  (45)),  and  fact  The  elastic  of  expressions  energy;  by  extremely  is  the  former.  the  cross  electron  shell  is  39  Q ( £ ; i) whe r e :  = N (7re /I ) 4  e  the  g  2  ionization  (E/I),  T H  cross  section,  Q  =  E  =  energy  I  *  ionization  =  number o f e l e c t r o n s which could observed i o n i z a t i o n ( e . g . , N =l atom, * 2 f o r He, H , e t c . ) ,  N  e  of  the  impinging  potential  electron,  of  the  electron  shell,  l e a d to the f o r the H  e  2  e  g Although naively with  = T H  the  U)  simple,  1  of  problem  Initially, kinetic  with the  the  difficult out that  over  a  comparable  to  that  that  agreement  (74),  attempt  more of  the  to  justify.  the  velocity from  a  encouraging  energies  the  he  The  latter  (It  s h o u l d be  stationary.  to  have  mechanical  by  Smith  very  but  has  pointed  chosen  a  considered  treatment  M o i s e i w i t s c h and  quantum  this  potential,  (75)  is  Born  e.g.,  as  electron  distribution  for  wide  approximation  ionization  distribution  (see,  electron  atomic  agreement fairly  reinvestigated  target  treatment  success.  to  predicted  the  energies.  velocity  low  1959  the  detailed  greatest  at  eliminate  considered equal  is  in  to  considering  particular  almost  sections  calculations  he  seem  cross  The  an  calculations  experimental  Gryzinski  distribution  the  very  energy  subsequent  2  gives  72).  in  1/x ) .  and  reference  in  involved  the  charge.  method  range.  Approximation Fig.  (1/x -  -  approach  absolute  energy  electronic  in a  met  out  that  Gryzinski (45)  is  point  different  treatment  a  of  from atoms.).  40  Using  t h e same  ionization  to  notation a single  Q(E;I) g (x) G  -  If  more  a  than  one s t a t e over  the G r y z i n s k i  attempt  variety been  theory  o f Thomson's  4  gjh (  X  is  that  experimentally; become  that at  cross  (72,  original  75,  76).  relationships sections  successful  D  r  of  of these  expression  (E/I),  these  describe  are d i f f i c u l t  sufficiently  until  to  i f  paper. is  collisions.  properly  predict  cross  or impossible  such  accurate.  theory  electron  theories,  can be used  least  i n Drawin's  or empirical  to  o n known s y s t e m s , for species  application  l h ( 1 . 25x) ] .  a classical  hoped  states  necessary.  empirical  are mentioned  not s a t i s f a c t o r y  it  g  2  2  process,  formula i s :  H 0 .66  formulae  1  is  of the  the i o n i z a t i o n  * N ( e /I )  ultimately  and I)  One o f t h e more  e  ln[2.7+(x-l) / ]  i o n i z a t i o n phenomena  Q(E;I)  =  g  available  The Drawin  empirical  theories  of N  (77).  Clearly,  study  where:  o f the i n d i v i d u a l  are several  to p r e d i c t  gDrU)  evaluated  there  formula for  i n v o l v e d i n the i o n i z a t i o n  to  a modification  where:  sections  (E/I),  G  2  values  of systems.  Drawin  However,  is  examples  Finally,  Other  g  the c o n t r i b u t i o n s  are several  by  the G r y z i n s k i  i s :  2  3  There  has  4  e  the appropriate  a  state  = N (Tre /I )  (with  which  above,  (1/x)[(x-1)/(x+l)] / {1 +2/3[l-(l/2x)]  summation  of  as  a time  as  to  quantum  }.  41  2.3.3  A u t o i o n i z a t i o n by The  from  the  phenomenon  direct is  excitation  directly  said  Autoionization, initial  discrete of  the  continuum. discrete to  in  escape  commonly  the  of  has  be  fairly  been  occur  by  the  These of  electron  points  make  to  of  continuum.  hand,  two  is  a  of  an  Subsequently,  there  is  more  into  states  there  has  results  on  the  prevalence  discussed  phenomenon  of  and  (78).  it  While  the of  threshold the  law  phenomenon.  to  contribution  which  autoionization  there  indeed  is  make  much a  it  considerable  order  ionization  seems  does  in  ion  is  ultraviolet  autoionization  been  nature  the  eventually  experiments,  the  of  permits  vacuum  on  potential  mixing  The  that  a  ionization  functions  theoretically  established  positive  does  and  into  radiationless  this  and  produces  ionization  wave and  photoionization  impact,  the  mix,  distinct  process.  electron  a  electron.  understood  be  the  ultraviolet  step  accessible  continuum,  excited  in  the  precise,  Historically, autoionization  medium  the  and  will  exciting  ionization  excitation  system  quite Direct  above  centered  process,  an  is  above.  energy  and  well  assessment  would  in  indisputably  controversy for  the  the  observed  when  the  ionization  photoabsorption to  is  discussed  other  continuum  access the  the  To be  and  the  Impact  auotionization  occur  into  lying  species. of  to  on  event  state  transition  of  ionization  ionization  The  Electron  make  some  efficiency evidence  significant  type  curves.  that contribution  42  to  electron  generally  impact  accepted  responsible  for  ionization linear the  or  onset  near  a  of  in  electron  impact  show any  direct  does  excited  in  the  not  Mann  can  be  (80),  routinely  of  Some  seen  observed  which and  are  difficulty.  Also,  structure  a  various the have  be  photoabsorption  in  atoms  lack made  of  and  the  would  be  molecules  this  of  with  additional  behaviour  Burns  This  ion  or  to  correlate  Also,  of  "break"  of  monoenergetic  and  examples  work  (81).  the  of  nature  correspond  not  threshold  it in  is  often  electron  strongly  the  for  the  (79),  additional  Blais  structure  detailed  of  the  impact  Hickam  appear  molecules  impossible  has  (81)  been  supposed  to  be  under  study.  threshold  interpretation  law of  correlate with  from  has  of  very  to  curves  autoionizing  envelope  can  knowledge  the  the  studies.  curve  ion.  an  autoionization.  structure  known t o  does  excellent  in  to  the the  Hickam  ascribed  which  solely  the  many  atoms  is  series  Each  would  However,  a  on  wherein  various  curve  Nevertheless, the  process,  follow  and  curve  were  of  previously).  the  on  state  consist  It  impact,  (depending  state.  studies  ionization.  structure  of  electron  would  discussed  curves.  ionization  by  segments,  slope  known e x c i t e d  structure  and  an  structure  ions  ionization  produced  efficiency  direct  curve  linear  new  if  producing  laws  change of  that  efficiency  threshold  marked  ionization  levels  photoionization  discussed  this  autoionization different  These for  in  factors  and  autoionization  monoenergetic  43  electron or  impact  ionization  efficiency  curves  difficult  impossible. It  law  for  has  excitation  would  be  there  exists  not  be  is  a  a  of  cross The  electron  rise  very  volt  above  excitation  above  threshold.  cases  excitation  of  von  (85). It  impact a  autoionization)  83).  However  this  might  This  evidence  excitation  generalization,  regarding  functions  as  a  and  then  often  the  behaviour  follows  slowly, some  which  excitation  one  fairly  electron  quickly.  exhibit and w h i c h  tens  optically  exchange  of  volts  forbidden  appears  to  be  states  intermediate  b.  illustration  helium  for  transitions  increase  of  states  within  decrease  allowed  which  for  requirement  a maximum u n t i l  and  A clear  that  threshold  to  (82,  rule.  As  made  a maximum,  electron a  evidence  (84).  be  The b e h a v i o u r  requiring  Engel  to  reach  c)  between  exchange  Optically  do  energy  electron  can  the  sections:  functions  not  of  that  prerequisite  applicable  states  threshold,  often  believed  excess  excitation  steeply  b)  not  generally  comments  a)  of  experimental  discrete  excitation  been  necessary  measurement  following  require  (the  function  much as  the  functions  of  step  true  from  the  generally  has  that  been  of  these  points  p r o v i d e d by  exchange  for  the  Corrigan  and  processes,  because  of  44  their to  threshold  conspicuous  efficiency  behaviour  autoionization  the  results  measuring  the  show  Recent  of  a  The  over  Christophorou  and by  section  be  demonstrate variety  published  the  of a  measured  contributors  ionization  1  threshold  Brion  (which  of  article  and  and  at  His  results (87)  Eaton  clearly threshold.  and  (89)  using  relative  electron  SF  similarly  processes  (108)  impact  fe  cross  threshold),  Collin  the  for  near  exchange  cross  from  above  Reinhardt  the  of  integrated  energy  the  inelastic  excitation  excitation  these  on  of  for  method  nitrogen  permit  directly  available  of  electron  eV.). for  is  techniques  preset  and m o l e c u l e s .  review  new  Huebner,  importance  atoms  a  exchange  (9),  claim  angles,  and  Compton,  techniques  to  than  of  the  to  by  scavenging  a  in  measurement  all  (86),  predominance  this  trapped  the  less  mercury  studies  for  process  (usually  for  the  major  structure  near  permits  integrated  threshold  the  relatively  sections  87)  threshold  helium,  two  processes.  (86,  sections  evidence of  cross  excitation Schulz  be  curves.  Further from  might  has  in  recently  "selection  rules". Unfortunately, evidence  that  exchange  state  autoionization observed  by  could is  there  prove  that  responsible  structure,  Nottingham  is  but  (90),  little  initial most  the  shape  Blais  experimental  excitation  for  by  direct  to  an  conspicuous of  and  the Mann  structure (80),  and  45  by  Hickam  (81)  metal  atoms,  Burns  (79)  and  were  2.4  give  direct  The  them  ion  of  negative  ions  electron  are  be  removed  structure. radiation place  with  and  the  the  collision  unimportant  has  is  via  the  in  ion  an  to  order  a  are  low  is  present  In  free  and  The  work  and  the the energy  stabilize emission  a  energetic  to  the of  former  pressures  These  onset  general,  and  only high.  impact  whereby  (Chap.  high  but  curve.  probability, at  allowed  additional  state)  stabilization.  states  electron  reversion  the  (81)  optical  curve,  impact.  to  Hickam  its  a mechanism whereby  in  this  by  the  mechanisms  of  by  optically  to  the  excited  mechanisms  important  the  six  capture  exists  the  in  electron  an  with  under  being  respect  gases  with  that  states  of  listed  with  frequency  for  these  of  forbidden  contribution  f o r m e d by  extremely  latter  say  Ions  collisional  an  to  Negative  there  from  not  no of  (perhaps  Two s u c h and  rare  experienced  optica1ly  a break  unstable  unless  in  curves  consistent  i.e.,  formed  species  electron,  be  if  appearance  (3)  can  is  difficulty  is  make  ionization;  negative  can  This  the  Hasted  (91)  explained  behaviour  Formation  neutral  the  observed  autoionizing structure  states  threshold  might of  be  responsible.  autoionizing the  Morrison  zinc  would  ionization efficiency structure  Similarly  correlating  spectrum  the the  and by  argument. in  in  takes  8 ref.  mechanisms  consequently,  3)  where are they  46  will  not  be  negative  2.4.1  covered.  ions  from  attachment (only  and  because  negative  ion  employed  in  mechanism is  ion  of  to  being  absorbed The  hypothetical  species shown the  AB.  the  case  curve  A in  ion  As  electron below If  a  is  of  considered.  which  the be  radiative  from they  consideration, would  negligible),  of  neutral the  of  experimental  molecular  the  molecule. the  fragment  energy  and  dominant  negative In  a  stabilization  of  situation  can  v i s u a l i z e d with  potential  energy  where ion  is  are  its  the  so  in  lowest  repulsive. to  ground  seen,  affinity  shown  the  for  Fig.  In  potential The  and  B is  considered  that  this  corresponding  to  the  the  Franck-Condon  Principle,  a  the to  of  Fig.  the  aid  diatomic  energy  la  is  curve limit  negative  have  positive  formation which  of  a  of of  neutral  atomic  dissociation  that  the  dissociation  formation  state,  emergent  diagrams 1.  the  negatively  energy be  ions  negative  for  two  to  conditions  parent  required the  make  the  of  attachment,  kinetic  corresponds  s pe c i e s B".  would  with  These  negative  this  B.  as  formation  processes  stabilization  into  fragment,  be  attachment  under  dissociative  particles.  the  dissociation  dissociates  charged  work  the  not  contribution  formation  for  direct  Attachment  collisional the  the  will  excluded  this  confined  process  of  atoms  Dissociative Having  Also,  limit  lies  neutral  declares  A and  that  the  Figure  1.  Potential  Lnergy  Curves.  48  internuclear  separation  appreciably the  transition,  vertical normal  on  the  then  the  in  on  wave  the  will  by  the  energy  Ej  for  the  the  species  a  and  case  minimum  Ej-D.  take  It  B"  kinetic  cease  should  respect  autodetachment separation  the  of  shorter  than  the  the  the  section  case  cross will  have  corresponding (the  curve form  of  are state,  vertical overlap  probability  is  be  at  be  the the  be  of  B"  for of  the a  observed  e")  be  with  limits  the  AB" is  initial  the  very  if much  possibility  small. of  energy  will  share  with  Thus,  c  energies  2  that  will  until  the  E  difference  r .  then  the  note  that  production  peak to  +  of  will  to  energy  unstable  than  period,  an  energy  mentioned  greater  observed  transition  (AB'+AB^*) is  at  worthwhile  from  approximately  experimentally  is  will  formed  compound s t a t e  production  the  be  AB", will  a vibrational  observing  argument  ions  g i v e n by  collision,  internuclear lifetime  It  furthermore  the  B" to  formed  energy  a  molecules  dashed  transition  being  in  electronic  the  to  as  Since,  the  ground  usual  applied  represented  of  within  change  arrow.  that  product~of to  the  illustrated. A and  be  not  is  diagram.  the  maximum  shows will  of  place  By  the  can  majority  level  does  process,  energy  vertical  la  diatomic  latter  vast  diagram.  Fig. an  the  functions,  indicated  the  v=0  the  excitation  potential  the  transition  lines  the  experiment,  initially  of  during  of  The B~  shape  for  this  limits  E^  depend  and on  of  E  2  the  of  49  detection  sensitivity Fig.  lb  shows  attractive  potential  this  B~ ions  case,  limit t .  D of In  2  and  the  the  energy  this  of  transitions  and  separation  the  As  cross  have  the  However,  be  an  be r .  The  £  energy  for  the  case  of  curve a  peak  peak in  the  the  the up  of  the  the  ion  will  production  case  for  D-»-E  2  have  briefly the  of  limits  would  kinetic  AB" formed  be  for  this  sharp,  internuclear  previously,  energy  In  energy  shared  region  covered  with  an  Again,  2  Ej+D  the  to  s h o u l d be  E -D.  until  ion.  dissociation  a minimum  energy  range  particular  negative  at  onset  by  fate  a  formed  with  possible  the  section  be  apparatus), for  onset  given  in  of  the  produced  in  the  curve  and w i l l  place  will  form  situation  have  a maximum  exceeds  transitions below.  will  taking  autodetachment  the  measuring  illustrated,  will  0,  the  energy  curve,  case  ions  of  of  ions  D and a  discussed  shape  B"  E  sharp  by  will  2 >  low-energy  side.  2.4.2  Ion-Pair  Formation  There abundant impact  on  mechanism relevant  are  production low is  two  other  of  negative  pressure  vapours.  ion-pair  dissociation  ions One  by  leading direct  commonly  production.  In  limit  potential  internuclear  separation)  a  charged  positively  mechanisms  of  the  corresponds  species  (A ) +  and  this  to a  the  to  the  electron observed  case, curve  the (large  production  negatively  of  charged  50  species which  (B").  is  because the  different of  the  former  molecule  to  a  inelastic  if  the  of  a  excitation  relevance  2.4.3  The  cross  to  a  large  an  electron  lifetime  last  to  involved  repulsive)  state  and  this  is  provided the  f o l l o w e d by  is  of  the in  Sec.  to  the by  cause  limit  energy  in  dissociation  sufficient  dissociation  given  mechanism  give  a  ultimately  radiative  Electron  of  a  the  dependence  2.2  is  of  (in  be  Reinhardt  (93, and  polyatomic  electron  have  negative  long  to  the  sec).  and w i l l  measured ions.  is  in  the  in  molecules. capture  with a  collisional  by  to  a  mass such  undergo  that  the  extensive lifetimes  excess  degrees  Hurst  study of  or  the  many  Christophorou, an  that  Although  thought  absorbed  made  ion  10"^  of  is  possible  observed  absence it  is  be  unstable  have  negative  capture  molecular  Compton,  94)  discussed  it  temporarily  available.  be  molecule,  stabilization),  can  Capture  to  (approximately  autodetachment,  process,  is  or  sections  sufficiently  is  freedom  capture  (attractive  discussion  polyatomic  spectrometer,  energy  processes  of  non-dissociative  In  ion  capture  excitation  above  Non-dissociative  leading  behaviour  here.  The  an  point  threshold  is  energy  involved.  electron  a  step  collision,  to  no  initial  discrete  has  dissociative  that  The  excitation  transition  production  from  fact  case.  an  state  Ion-pair  and  of  several  this  of  51  2.4.4  Theory  of  The largely  Negative  discussion  descriptive.  application  of  the  tacitly  assumed  e.g.,  diatomic  a  evidence  that  Sec.  2.4.1  of  dissociative  be  answered  to  a  attachment  field  theory  species  to  (and  inverse  which  might  was  further  Principle, its of  stands such  as  Because with  capable  the of  halogens the  distance,  a  and  valid  off  be  chance are  atom  in  picture  a n d why  was  energies. qualitative,  an  electron  experience  a bound  of  the  in  a the  neutral  be  distance  of  It Pauli  state  where  quantum  of the  unlikely  and  the  then  examples  in  a  state.  becoming bound.  decrease  attach  suggested),  to  to  this  r a p i d l y with  equal  would  arguments  should  considering  excellent  electron  of,  the  will  is  rapid  states  almost  accepted  of  has  that  shown t h a t  supporting  can  etc.,  experimental  place,  very  if,  the  from  electron  dependence  of  of  been  The main q u e s t i o n s  a simple,  hydrogen  has  ion  specific  has  far  qualitative  using  extremely an  exist,  at  electron(s) good  clear  first  quantum number  fairly  is  place  that  electron  outermost a  the  falls  suggested an  so  negative  why t h e  argument  which  be  ions  discussion  processes.  fifth-power  principal the  (95),  It  give  in  a neutral  force  the  of  do  are  take  mechanical  of  states  capture  should  proximity  is,  existence  indeed  Massey quantum  That  negative  molecule.  do  by  of  Formation  Franck-Condon P r i n c i p l e ,  the  such  in  neutral  Ion  to  number  it Atoms  this force  case. field  become  52  bound this  in  a  state  virtually  states  of  exacting  of  excludes  negative quantum  information negative  higher  on  the  dissociative  theories  to  a molecule  will  ion.  time  (95)  approximation  of  (95)  formation  the ,  not  other  the  regarding  nuclear  the  attachment  of  an  has  shown  that  if  the  energy  is  used  Hamiltonian diatomic of  electron  the  an  and excited  and  more  yield of  atomic  w o u l d be the  system  events  been  the  captured  then  in  these  the  the  this  ideas  as  a  for and  permit Stanton  (96)  nuclear to  the  neutral  would have  initially  cross  a  electronic  a bound s t a t e .  capture  of  (97)  applied  of  the  electron  known  would  describing  consisting  that  Born-Oppenheimer of  molecule  wherein  free  Bradbury  of  shown  production  has  and  a  general  processes  has  Specifically,  electron,  using  the  a perturbation  dissociative  hydrogen  a  operator as  (96)  independence in  two  describe  it  breakdown the  are  between  for  hand,  electron.  extra  to  acting  Bloch  functions  permitting  calculated molecular  for  plus  of  there  Stanton  account  work  that  wave  attempt  forces  and  effect  calculations  capture.  On t h e  from  Massey  kinetic  forming  considerations,  molecules,  which  electrostatic  negative  of  of  number,  ions.  such  some  These  possibility  of  and  quantum  possibility  mechanical  classes  simple  the  ions.  Proceeding  as  principal  Chen  section basis.  the  free (92) of  has  53  The ion  formation  resonance  has  been  which  scattering  simple  general  scattering  resonances, in  other  to  consider  phenomenon.  are  cross  sections,  as  the  by  a potential  of  reference  resonances particles  barrier  or  Much  originated atomic  of  nuclei,  consisting  of  In  case  considered  being the  T he negative atoms  ion  a  the  concept  and m o l e c u l e s much  of  elastic  sections.  As  an  below  lb.  the  temporary  the  the  is  known  the the  in to  consider the  result state  state  neutral  electron,  the  Chap.  theory  that  be  very  that  in  a  the  at  neutral  is projectile. is  variety useful  an ion.  of in  recently impact  situation curve  formation  eventually  the  temporary  has  cannot  of  negative  electron the  6  of  scattering  of  attractive  which  When t h i s  electrons  projectile  a wide  inelastic  to  of  incident  becomes  very  hypothetical  example,  of  formation  dissociation. an  for  and  structure  and  D will ion  the  states  example,  negative  and  such  anomalies  even  "compound s t a t e "  here,  proven  Excitations  energy  a  target  of  has  in  Fig.  it  "compound s t a t e "  discovered  in  and  resonance  (resonance)  interpreting  as  sophisticated  from s t u d i e s  formed  and  manifested  of  (see,  the  position  electron  of  well  energy  the  of  in  negative  a  existence  encountered  treatments  to  p r o b l e m as  one-dimensional transmission  70).  by  The  is  approach  the  experimentally  quantum m e c h a n i c a l  problems  theoretical  be  cross  illustrated of AB" of  a  stabilized  decays  species  been  to  could  the be  by  54  reformed  in  the  v=G  elastic  scattering  initial  energy.  this or  level. since  would  in  the  elastic  spacing  of  the  structure  spacings  of  the  presumed  to  take  the  neutral in  the  on  to in  populate the  sections.  evidence  for  Taylor,  Nazaroff The can  breakdown  be of  c o nsidering  of,  and  actual  the them  as  cross yet,  of,  either  vibrational  The  decay  the  predictions might  lead  these  in  resonance  the  to  structure  of  been  (92,  98)  performed.  and their  thought  experimental  article  by  (98).  of  molecular  negative  on  the  of  basis  phenomena.  calculations  section,  be  levels,  the an  is  of  current  and  contained  existence  the  levels  of  peaks  the  magnitude  summary  that  of  of  the  although  Both  energy few  ion  the  Born-Oppenheimer Approximations,  of  as  of  its  predicts  it  would  the  Golebiewski  explained  to  with  curves  regain  series  AB".  This  to  section,  vibrational  effects is  a  and hence  enhance  the  resonances  quantitative  have,  to  of  accordance  efficiency  permit the  in  An e x c e l l e n t  occurence  as  cross  level  process.  tend  theory  corresponding  higher  decay  generally  the  states  place  correspond would  itself  scattering  electronic  excitation  wou Id cross  resonance  Franck-Condon P r i n c i p l e ,  possible  would  electron  manifest  dips  of  the  However,  occurrence  This  or  by  theories dependence  such  calculations  55  2.5  Electron  Scavenging  Electron applied  to  electron of  the  a novel  impact  inelastic  the  method  cross  of  and  formation  of  (99)  S F £ . .by  energy  of  less  than  0.1  of  less  than  0.05  eV.  These  be  Curran  to  resulting  from  threshold  directing  detect an  collision  spectrum  in  threshold  the  has  been  inelastic  threshold  energy  a  RPD s t u d y  good  impact.  this  ion  and o v e r  Their  takes an  authors  also  process.  The  ion  is  using  the  production  impact  spectrum  beam  a mixture  of  a mass  function  agreement  technique  of  (86).  nitrogen  SF^  with  that  N  overall  known  an electrons recorded by  by  process  2  by  vapours The  energy  found  the  (produced  and  electron  on  He  spectrometer.  of  The  energy  electrons of  range  not  as  process. for  at  process.  SF^  zero  collision  place  remarked  of of  results  energy  potential  into  a  careful  the  chamber as  made  a primary  a monoenergetic  current  that  by  electron  the  SF£  name  energies  inelastic  RPD t e c h n i q u e )  of  eV.,  this  higher  the  of  for  realized  (6)  indicator  a  at  have  production  section  produced  near  electron  an  to  the  Fox  that  cross  the  investigating  sections  indicated  high  is  process.  Hickam of  scavenging  in  record  gave  a  another is:  * e" has  zero  The  second  + N -»- N 2  energy step 8  E  +  2  • e~  ,  where  at  the  threshold  of  the  scavenging  SF -SFg, 6  for  the  scattered  the  process  electron  production is  simply:  of N  2  <  56  The  technique  Jacobs  and  as  scavenger,  the  authors wide  have  and  the  of  helium The  to  a  Sec.  2.1).  optical  often  Compton  excellent  have  spectrum fact  the  the  extent the  that  be  states.  As  was  mentioned  may  play  a  ion  ionization  that  a  gained  role  in  et.  technique  temporary  scavenging  spectrum.  particular  resonant  vibrational nitrogen.  The  (9)  fact  of  that  the  threshold  Indeed  and  leads  (see  that  forbidden  the  study  relative  expected  the this  is  transitions  valuable  location  2.3.3,  of  forbidden  structure  be  have  used, ion  in  such states  positive  (31)  is  in  special  has  ground  appears  shown  that  cases,  They  manifested  largely  the it  demonstrated  states.  was  Schulz  excitation  naphthalene,  curves.  in  state  to  a  selector.  the  spectrum,  Sec.  for  resolution  violated.  producing  negative  known r e s o n a n c e  be  optically  in  al. can  at  latter  Approximation  regarding  efficiency  Compton  might  scavenging  can  large  Born  w o u l d be  spectra  of  by  iodide  The  electron  of  information  observe  127°  breakdown  the  (9).  a high  measurement  it  methyl  from h e l i u m  performed  rules  from  threshold  is  dominate  scavenging  a  investigated  al.  performed  Consequently,  to  et.  ranging  using  that  I"  section  selection  observed  who u s e d  and by  (89)  cross  complete  subsequently  substances  Eaton  inelastic  (100)  produced  variety  Brion of  Henglein  was  in  the  that  electronic the  to  discovered  responsible  in  the  this for state  scavenging  the of  57  spectrum  indicates  the  temporary  the  neutral,  comes  negative so  o f f with The  predicted explain  that  speculated  that  responsible repulsive  zero if  similar  structure of H  If  this  state  of  were  would  might  produce  produced  in direct  sensitive  probe were  electron  as  by T e m k i n ,  2.3.1)  would  increase  of  of the  of  impact  (160)  Bhatia  law f o r e l e c t r o n predict  that  in proportion  to  the  to  zero  this  this  or  energy  (160). electrons  impact  of the i n c i d e n t the  the q u a n t i t y :  i f  energy.  theoretical (65)  ionization  energy  be a  particularly  and S u l l i v a n  zero  experiment.  i o n i z a t i o n would  that  event,  scavenging  by Temkin  zero  near  This  i n a scavenging  a function  approach  is  i n the Franck-Condon  of the i o n i z a t i o n process,  he has c l a i m e d  threshold  intersects  suggested  Specifically, used  which  of the i n t e r s e c t i o n .  the y i e l d  studied  have  E'g of  2  to  dissociative  (98),  an e l e c t r o n  been  in  been  autodetachment  application  that  has  In a t t e m p t i n g  a l .  curve  be d e t e c t a b l e  further  He h a s p r e d i c t e d  the  et.  the case,  those  autodetachment  e V . , i n the  the n e u t r a l  has r e c e n t l y  yield  occurrence  11  , Taylor  i n the r e g i o n  occurs,  technique  2  near  in  in  energy.  molecule.  the r e p u l s i v e  ^ E * curve  One  this  zero  levels  match  ejected  f o r the d i s s o c i a t i o n ,  energy  it  closely  the e l e c t r o n  f o r the hydrogen  curve  vibrational  ion state  following  attachment  neutral  certain  essentially  certain  region.  that  to  derive  (see S e c .  yield  should  (E-iP) / . 1  2  58  Similarly, app r o a c h  Temkin used  were  correct,  as:  ( E - I P )  be  obtained  0  (160)  by  Wannier  then ,  1  2  7  from  .  scavenging  results  described  a  from  technique. by  zero  Schulz  to  this  it  should  the  (86).  that  of  if  the  yield  type  the  threshold  would  increase  information  can  experiment. be  mentioned  s h o u l d be  previously  The  out  derive  energy  scavenging  experiments  gained  electron  the  pointed  (69)  Clearly  Finally, of  has  latter  that  comparable mentioned  technique  has  the with  results the  trappedbeen  fully  CHAPTER  III  INSTRUMENTAL  Of be  described  has As  the  was  this  effort  this  thesis,  devoted  to  designing  mentioned  in  Chapter  been  in  total  investigation,  version  was  electrostatic  these  and  far  and  I,  a  in  the  the  largest  instruments  the  initial  discussion  the  research  will  be  evolved  the  radio-frequency  instruments  instruments.  stages  of  to  portion  d e v e l o p i n g the  two  in  After  analyzer  spectrometers,  by  although  employed.  expended  a  from  third  127°  mass  described  in  some  detail.  3.1  The  Electrostatic Since  analyzing  electron  instruments and In  the  were  Analyzer turn  energies  used  inverse  Hughes first  generated properties uniform  and  power  between for  theoretically  the  century,  have for  field  Rojansky  as  coaxial  field.  been  the  These  in  use.  might  authors  out  such  similar  optimum f o c u s s i n g  The  filtering  field  capable  of  early  spectroscopy  pointed  cylinders  particles  devices  beta-ray  (101)  electrostatic  charged  magnetic  the  mainly  employed a magnetic 1929,  of  that  as  have to  agent an  would  be  focussing  those  proceeded  properties  (10).  of  of to  the derive  the  device.  60  (A  summary  of  this  Simultaneously. verified  the  Hughes  a  given  coaxial  cylinders,  that  electron  injected  into  will  execute  with  the  Hughes  velocity angles after it  maximum  and  but  plane at  at  0°,  127°17',  having  the  energy  design  a  I).  experimentally  orbits  injected can  at  desired  be  this  of  a  at  two  coincident  It  was  the  point,  at  but  a  at  field.  would a t t a i n Thus,  line  common  Also,  entering  slit  in  of  a maximum  a  if  source  intensity  be  a  by  refocussed  the  angle. or  shown  having  same  of  surface  in a  plane  the  as  a  electrons  will  the  device.  Clarke's  demonstration  used  to  from  a  been  equipotential  electrons  a point  such  being  w o u l d be  segment  will  and  center  the  between  velocity  electrons  this  point,  the  electrons  operating  an  intercepted  velocity  has  to  two  of  at  from  c o u l d be  research  velocity  velocities  separation  strength  cylinders.  127°17'  different  resolution  and  (102)  equipotential  with  analyzer  of  Appendix  unique  about  field  the  and  monoenergetic deal  in  field  a  this  that  that  they  be  the  the  through  the  parallel  of  an  Following 127°  will  (101)  - a to  are  of  motion  center  spatial  electrons  field  entering  shown  normally  there  Rdjansky  passing  was  value  circular  and  +a  McMillen  possessing  the  common  and  and  appears  predictions.  For  an  derivation  form  a beam  thermionic  devoted  conditions.  to  (25)  low  source,  finding  To be  of  that  the  useful  the energy  a  great  best  for  most  61  experiments must of  be  capable  current  However, in  this  high a  r e q u i r i n g a monoenergetic  with  it  an  energy  that  currents,  the  used  to  produce  tungsten solid held  mesh  metal at  being  was  reflected  from  arrangement, and  be  the  most  the  removed  and  in  possible  through  a  field  with  The  grids  of  the  of  undesired  space  and  were  placed which  behind was  In  through  of  making  at  low  terms use  with  electron  approximately of  10"  7  the  the  in  the  this  plates.  This  for  were  previously  region.  reduce  energy  transparent  being  low  further  electrodes  energies  c o u l d pass  suitable  space  metal  charge  field-forming  working  an  produced  the  rationale  from  at  mV.  workers  fields  electrodes,  electrodes  selector  100  relatively  90%  experimented  pass  than  early  with  also  to  less  internal  these  breakthrough  to  amperes  8  selector  (26)  order  10~  cylindrical  catcher  electrons  analyzers  Kerwin  catcher  solid  from the  important  material now  the  the  dealt  the  potential.  electrons  these  electrostatic Marmet  by  called  much  the  selector  and w i t h  in  the  (26)  Outside  that  of  a  width.  Kerwin  grids.  a positive  caused  distorted  electric  plates,  arrangement  beam  replacing  the  to  energies,  electron  and  order  evident  distribution  p r o b l e m by  the  d i s t r i b u t i o n of  low  which  Marmet charge  of  became at  the  charge  increased  passing  quickly  field  space  of  beam,  was  new  grids  probably  energies.  manufacturing  reflectivity space  A.  1 eV.,  of and  charge.  It  electrons to  achieve  is  62  distributions  of  less  A further in  operating  magnetic energy  a  devices  beam  is  severely  fields. taken  This  if  a  to  has of  operate  appear  to  be  caused  pass  in  order  (e.g.  10"^  of  why  operated  by to  by  stray  in  A low  even  extreme the  be  although to  are  large  very  weak  precautions  ion  Most  source  behaviour  to  is  since  are  still  many  the  problems  that  When t h e y low  extent  selectors  are  operated  intensity  much m o r e  stable  and  predictable.  3.2  Quadrupole E l e c t r i c The  electric  field  to  mass  their  Paul  and  Field  feasibility to to  Raether  of  technology  devices  of  currents  of  the  great  sensitive  useful. beam  a  these  factors.  the  their  that  (25),  and  a primary  A.),  affected  developed  Clarke  uncontrollable  analyzers  is  that  encountered  trajectories.  reason  mentioned  selectors  difficult  one  been  spectrometer.  be  p i o n e e r i n g work  influence  electron  selector  mass  must  is  virtually  as  the  electron  electron  must  is  the  be  very  p r o b l e m w h i c h has  on  It  the  general  mV.  have  conventional  of  50  fields  magnetic must  these  than  of  separate  Mass using  charged  a particular particles  charge  ratio  (37).  A subsequent  co-workers  gave  a  rather  more  quadrupole  mass  spectrometer  was  Filters  first  (38).  according  demonstrated  paper  detailed  quadrupole  by  Paul  treatment  A second  type  by  and  of of  his  the mass  spectrometer quadrupole described  which  field  fairly  be g i v e n  illustrated electrodes function other  4> (ctx 0  Laplace's  Also,  linear  2  2  equation:  amplitude  (x  o+3+Y  x and y  a,  spectrometer arrangement is  (defined,  a  along  potential  a=-g  =  of  with <)> w h i c h i s :  by mass  l / *  0  ,  Y=0.  to b e :  a D.C. voltage  applied  an A . C . v o l t a g e  Therefore:  is  linear  coordinates  as:  chosen  represents u.  theory  For the quadrupole  are chosen is  covered  8 and y a r e r e l a t e d  " 0»  instruments  of this  which  A general  U represent*  V and p e r i o d  2 -y )  where  and V c o s ( u t )  <(> =  of  (U + V c o s (u>t))  2 /  r  . The equations of motion of a unit charge 32 a n d m a s s mm u n d e r t h e i n f l u e n c e o f t h i s p o t e n t i a l a r e : 3t o Q  x  e  where  i n the quadrupole,  rods,  field  i n the s p a t i a l  the c o e f f i c i e n t s  o  2  ) ,  mass  particular  an e l e c t r i c  a field  <j> = U + V c o s ( u t ) , the  This  of these  description  i n F i g . 2a) .  + yz  of a  i n v e n t e d and  completely  The q u a d r u p o l e  produces  +$y  the operation  a brief  i n F i g . 2a.  2  instrument  and has been  so only  quantities  filter,  behind  here.  properties  (39).  of the coordinates  produces  <j> *  theory  (38),  the f i l t e r i n g  t h e monopole  complicated  elsewhere will  is  by v o n Zahn The  is  uses  to  64  Y /1\  r  rod =  1  -  1 6 r  o  •U • V COS (w t )  V cos(wt) U -V costw.t)  ->  U .VcosCwt) Figure  2a.  The  Quadrupole.  Y  U v Vcos(wt)  Figure  I- i g u r e  2.  Quadrupole  2b.  and  The  Monopole.  Monopole  Mass  Spectrometers.  X  65  The  third  equation  parallel was  to  shown by • 2b  cot  the  is  q  (as  two  equations  called a  rods  Paul  made,  and  et.  be  stable  x  /  mw r 2  ion the  the  are  the  As  variable  introduced, in  velocity field.  dimensionless  change  parameters then  the  standard  equations.  b  a  first  form  The  2q  cos2b)  d y/db  2  -  (a  +  2q  cos  (38)  and M c L a c h l a n  of  rather  x  a  to  the  the the  •  (103)  of  so-  parameters  solution  the  Also, rod  so-called  region  where  with  0 0. have  discussed  equations, are  for  b.  must  remain  stability  into  case  the the  for of  for  value  unstable  less  are  case  of  x  and  y  an  ion  to  the  diagram  solutions  these  divided  an  for  stable  and  a bounded  For  excursion  both  2  Q  yields  solutions  system  2  they  whereas  the  mtf T .  C o n s i d e r i n g the  simultaneously  field.  shows  2b)y  that  infinity  be  of  in  infinity,  must  the  «  categories. stable  to  tends  novel  /  x  Mathieu d i f f e r e n t i a l  directions  shows  q=4eV  +  tends  center  ;  (a  filter,  through  2  become:  and u n s t a b l e  as  0  equations  mass  It  by  if  •  direction,  3  two  written  quadrupole  Fig.  (38),  2  are  solution,  the  the  altered  d2x/db  al.  solutions  x  if  that  are:  solutions  the  not  al.  and  differential  the  says  Mathieu d i f f e r e n t i a l  2  of  et.  can  a=8eU  Paul  is  d e f i n e d below)  and q  The  simply  ion  the  stable  pass  from  than for  the  r . 0  quadrupole. as  a  67  function  of  the  parameters  Experimentally by  choosing  magnitude On a  the  a  of  line  Fig.  such  line,  because  this  for  q)  the  high  Zahn  at  r  0,  in  many one  to  and  causes to  a vs.  the  a  stable  strip  q plot. on  the  This  near  region  stability  Included  been  chosen  the  mass  figuratively and  are  transmitted.  line  should  so  that  only  a  stable  the  there  at  of  As  illustrated  quadrupole Note,  not  monopole  to  for in  permitted. be  boundary  is  indicated  by  Fig.  3.  and that  (grounded)  stability  in  Fig.  however,  y  diagram  the  field,  electrode  are  range  time.  situation  an y  any  intersect  narrow  the  only. is  the  the  q.  As  are  along  scan  of  of  has  region  respects.  region  and  diagram.  that  values  spaced  by  the  stability  negative  small  cross-hatching  y  a  slope  masses  apex  fourth  of  generate  determined  w o u l d be  stable  shown  quadrupole  thus  the  to  w o u l d be  w o u l d be  has  the  would  The  resolution,  varying  operation  stability  the  by  operated  constant.  dependence  line.  be  ratio  masses  the  (39)  uses  of  which  can  and  the  individual  near  corresponds  contrast  the  masses  similar  monopole  in  limited  diagram  Von  mass  into  mass  hence  mode  of  scan  the  line  and  is  stability  =  typical  scanned  along  (a,  an  the  intersects  stability  This  of  it is  this  individual  that  monopole  on  The  quadrupole  holding  slope  a  Clearly,  2b,  the  q.  U/V r a t i o ,  V while  q diagram,  and  the  the  is  moved  the  of  3  spectrum  of  U and  U/V r a t i o .  this in  value  vs.  straight  the  a  a  Note  68  further  that  resolution  the  only  slope  minimally  A very these  (104).  Typical  have  Lever  and by Dawson  3.3  The  been  this  work.  127°  electron  electrons.  affect  discussion  has been  ion trajectories  the  of  g i v e n by in  these  by Brubaker  and Whetten  instruments  A l l three  shared  selector  However,  as  the  the i o n beam.  described  d i d not  collector  was u s e d  the  qualitative  illustrated  analyzing  and  will  (104),  (106).  Instruments Three  second  line  monopole.  instruments  instruments (105)  scan  i n the  instructive  radio-frequency  Brubaker  of the  instrument third  Subsequent detection  used  used  referral system  as  the  three  mass  register  a means  of using  of  the  monoenergetic  differed  i n t h e method  instrument  analysis. the  mass  mass  of  to be  A total  ion current.  ionization The  spectrometer,  spectrometer.  instruments of  course  of  a monopole  these  i n the  feature  the source  a quadrupole to  used  The f i r s t  feature to  were  will  identification.  use the i o n  69  3.3.1  The T o t a l The  very  simple  p ro duce  Ionization  total  served  to  record  inelastically  chamber  was  housed  entire block  diagram  scattered  i n a bakeable  a  selector  dimensions  of  ultra-high  beams,  these  were  individually  spacing  strands  of these  appears  of  a  simple  The i n s t r u m e n t The  i o n chamber from  i n this  type  304  i n F i g . 4.  to  at  the g r i d  w h i c h was a p p r o x i m a t e l y  of  grids  transparent  were  portion  1.0 of  and 1.5  the  grid  of  wire  supports.  by g r o o v e s  a spacing  a grid the  were  The g r i d  tungsten  was c o n t r o l l e d  supports  system  An e x p l o d e d  gold-plated  spot-welded  wires  the end o f the g r i d  the  and a n a l y z e r  components  which  radii  and to  vacuum s y s t e m .  the s e l e c t o r s ,  to  which  of the s e l e c t o r  and c o n s t r u c t i o n .  0.002"  gave  127° selector  127° analyzer  electron  a  steel.  were  of  of  cup i o n c o l l e c t o r .  including  wires  The  a  was b a s i c a l l y  a n d v a c u u m h o u s i n g was c o n s t r u c t e d  identical  This  beam,  and a Faraday  The  in  consisted  the performance  apparatus,  stainless  The  It  a monoenergetic  ion  *  i o n i z a t i o n apparatus  instrument.  monitor  Instrument  85%  of  milled  0.016".  transparent.  c m . , and t h e assembly  length  was 6 . 6  cm.  * I w o u l d l i k e t o e x p r e s s my a p p r e c i a t i o n t o D r . G . J . K r i g e for his assistance and a d v i c e d u r i n g the p e r i o d i n which t h i s i n s t r u m e n t was b e i n g u s e d .  gure  4.  E x p l o d e d View  of  a  127°  Electron  Selector  71  The  catcher  electrodes  and  positioned The  can to  be s e e n  was  held  from  grid  i n the  0.5  but b r i e f l y ,  support nitride  correct  end p l a t e s .  dimensions  by  applying  instrument length end slit  thickness  workers  to  described  plates  were  selector  insulated  bolts,  chamber.  The e n t r a n c e  t h e same  separation was into  the plates  were  screwed  support  were:  length  Rather,  would  to  at  have  it  at  the  0.18", the  been  i n the  was n o t d o n e was h o p e d  minimize this  maintained  =  = 0.015"  f o r end e f f e c t s This  extending  directly  the end p l a t e s  them.  here.  always  grid  slit. used  selector, i n the  that  problem.  the p o t e n t i a l  the The  of the  plates. The  were  that  to  of the s e l e c t o r  The i n n e r  of the p l a t e  correct  a voltage  through  containing  The s l i t  other  attached  Finally,  plates.  by  were  pins  end  be m e n t i o n e d  units  p o s i t i o n by c e r a m i c  slits  should  spacers.  the s e l e c t o r  passing  spacers.  and e x i t  It  of  held  nitride  end p l a t e s  by b o l t s  entrance  =0.02",  c m . , were  by b o r o n  details  the  width  and 2.0  supports  constructional  boron  these  radii  i n the g r i d  i n F i g . 4,  the outer  insulating  of  onto  via  containing  and e x i t  slits  o f t h e i o n chamber  as  the s e l e c t o r  the monochromator  The i o n chamber  of the  mounted,  block  the mounting b l o c k .  direction  were  the metal  dimensions  between  0.020".  and a n a l y z e r  electron  Its  itself  The  and t h e i o n chamber was a c a v i t y  dimensions  beam)  slits.  the i o n  x 0.6"  were  x 0.6".  milled  0.4"  ( i n the  The i o n  72  chamber plate This  exit  slit  for  electrically permitted  The  sample  the  chamber.  a  gas  transparent  rough  was  admitted  90%)  b l ock  a position  allowed An  to  source  of  cup  diffuse  illustration  of  ion just  in  connected  to  pump b a c k e d  by  used  flanges  pumping which  lead  as  permitted  baking  by  a  obtained.  re s i d u a l  gases  conjunction  cold  350°C.  measured  sample  above  the  routinely  pumped  liquid  to  of  cold  trap the  This the  this  shown i n  Fig.  with  of  of  ions  were  collector. 5.  The  a stainless oil  trap.  The  gaskets  assembly  to 9  an  An a l l  10~  glass  leak  8  mm.  were  contribution brass,  the  oven,  and  i o n i z a t i o n gauge any  were  chamber, in  10"  steel  diffusion  contained  between  sintered  instrument.  the  electrically  wire  minimized  a  and  rhenium wire  Silver  entire  results.  of  shielded  this  trapped  were  Bayard-Alpert  block.  flux. top  The  or  a  slit.  pump.  the  the  through  grid.  ribbon  in  highly  to  consisted  Pressures  system  with  is  nitrogen  a mechanical  and  approximately Hg  chamber  entrance  a  extended  the  tungsten  the  A highly  this  ion  at  was  outside  of  electron  a pipe  collector  vacuum s y s t e m a  the  a h o u s i n g w h i c h was  selector  pumped by  all  a  of  grid.  apparatus  contained  on  mesh  contained  remainder  chamber  the  filament,  chamber  the  of  was  The  the  through  out  electrons  the  of  steel  Faraday  from  beam was  measurement  The bottom (>  electron  insulated  insulated t o  the  of  diffusion was  used  in  73  Figure  5.  The  Total  Ionization  Instrument.  74  In g e n e r a l , t h i s high  degree  produced and  by  the  by  of s u c c e s s .  The  intensity  the  was  low  selector  resolution  optimum  was  performance  At  interior  o f the  times,  ionization  carbon) i n order  but  improvement  such  as  Kerwin  the (26)  were not  3.3;2  "Electron or t h e  of  model, the  the  i n p e r f o r m a n c e was  suggested  as  instrument,  i n design the  the  were q u i t e d i f f e r e n t  frame  later  A.)  9  the  produced in  this  the  with  Aquadag  reflection,  gained.  by  Marmet  by  McGowan  Surfaces and (40)  Instrument  Although  same d i m e n s i o n s  diameter  was  were  electron  V e l v e t " suggested  monopole  different  apparatus.  this  mV.  figures  beam  5 x 10~  c a t c h e r p l a t e s and  to reduce  gold black  Monopole The  very  electron  (100  described  a  used.  The  was  of the  chamber were c o a t e d  (colloidal little  These  the  meet w i t h  (approximately  f a s h i o n to be  various  d i d not  barely acceptable  achieved).  o p e r a t i n g i n the  chapter.  instrument  grids  to the  selector  in their  and  ionization  a n a l y z e r had  constructional  were c o n s t r u c t e d by  c o n s i s t e d o f a 127° metal  total  in Fig. 6  ones p r e v i o u s l y d e s c r i b e d ,  gold p l a t e d tungsten  central  illustrated  wire  brass  o f the  on  cylindrical  segment had  away l e a v i n g o n l y a b o r d e r s u f f i c i e n t  been  they  features.  winding  a grid  the  In  0.002"  frame.  The  segment.  Most  machined  for structural  strength.  SCHEMATIC OF ELECTRON IMPACT SPECTROMETER  76  The to  ends  the  facilitate  plated a  of  the  double-layer In  strips the  the  entrance  plated  itself  formed.  of  was  0.016"  gold  technique  of the s e l e c t o r ,  the grids  gave  field  i n appropriately  1 2 7 ° angle slits.  plate  This  end p l a t e s .  mild  associated  entrance  steel  with  The remainder  both  procedure h o u s i n g and  slit  i n order  the  Teflon  contained  The' f i l a m e n t  the s e l e c t o r plated  slotted  which  mounting  and  were to  current  reduce  flow  of the m a t e r i a l  was  of the gold  brass.  slit  chamber,  could  and w h i c h  completely slits  block on t h e  on t h e  important  was t h e d o u b l e 6  ; .  Not shown  be m a n i p u l a t e d could  the  field  by a p p l y i n g  would  i n this from  exit  box measured  Normally,  ionization  with  to  8.0  5.0 x  i n the chamber  illustration  outside  slit  box measured  box" arrangement,  potential.  innovations  be a d j u s t e d  electron  outer  inner  maintained  fringing  t h e most  in F i g .  which  "double  of  instrument  illustrated  be  the  gold  (107).  monopole  those  to  of  One  The  intervals  This  mounted  surrounding  filament  a  were  and e x i t  magnetic  at  The frame  were  version  eliminated  constructed the  grids  this  affixed  area  notched  grid.  plates  completely  were  the winding.  before  catcher  frame  the  a position of  mm.  With  fringing  a constant  inner-outer  change  during  to  mm., w h i l e  a constant  a single  vacuum  the inner box.  x 0.4  3.0  the  field  could  box  box a r r a n g e m e n t , a scan  is  of the  this  electron  77  energy,  and  this  efficiency, accurate  could  Also,  with  measurement  of  during  an  design  considerations  the  energy  conceivably  scan.  measurements  of  the  ion  the  electron  exit  slit  the  electron  flux  could  It  s h o u l d be  were  the  affect  electron  closed,  mentioned  implemented  in  collection  be  obtained  that  order  these  to  impact  threshold  to  monopole  an  facilitate law  for  ionization. The spectrometer introducing  ion was  consisted  of  of  diameters  4  the  is,  that  from  effectively beam  from  the  served  10  any  differentially  entire  Teflon source  insulating on  out  other ion  the  the  g u n was of  selector  pumped m o n o p o l e  curves.  were  could  grounded monopole  vacuum  enclosed. sealed  must  not  be  directly but  have  they  entered  chamber.  plate and  the The  which  served  simultaneously  chamber  electron  apertures  rings  trajectory,  and  avoid  was  It  ionization  a  the  path  insulating  which the  to  cylindrical ion  rings  mass  efficiency  plates.  ion  ions than  aperture  isolate  ionization  The  ion  point  the  entrance to  the  designed  containing  shielded  screened  of  into  mm.  the  carefully  plates  the  regions  termination as  and  between  emphasized visible  two  carefully  spaces  leading  similarly  distortions  It  That  source  from  the  multiplier  chamb e r . The r  0  equal  brass.  to The  monopole  itself  1.5  cm.  The  ion  detector  was  material was  a  27  cm.  was  sixteen  in  again stage  length, gold EMI  with  plated 9603  78  Venetian  bery1lium-copper electron  blind The  vacuum s y s t e m  pumped b r a s s chambers.  consisted  One h o u s e d  system, w h i l e the o t h e r housed electron trapped  multiplier/Each  o i l diffusion  Rubber o r T e f l o n flanges. was into  this  leaks  pressure orifice  was pumped by a l i q u i d  by a m e c h a n i c a l pump. to seal  into The  spectrometer  sample  inlet  Sample g a s e s  s y s t e m was flowing  o f the system,  performance i n this  o f the s e l e c t o r s  instrument appeared  distribution.  As can be s e e n , b o t h  the d i s t r i b u t i o n  base.  later  resolution  and mass  o f an e l e c t r o n (3 x 1 0 ~ A . )  the i n t e n s i t y Also,  8  t h e peak  o f the r e s i d u a l  at the  gases i n  r u n on t h e monopole mass s p e c t r o m e t e r .  o f mass peaks  procedures  i n this  a common  and d i d n o t show undue t a i l i n g  F i g . 8 shows a mass s p e c t r u m  operating  on t h e low  t o be h i g h l y  w i d t h were e x c e l l e n t .  was s a t i s f a c t o r y  t h e vacuum s y s t e m Unit  incorporated  t h e i o n chamber.  F i g . 7 shows an example  shape  Hg  through s e p a r a t e  and f e d t h r o u g h  satisfactory.  and  the various  s e p a r a t e s t o r a g e b u l b s were mixed  side  nitrogen  vacuum o f t h e o r d e r o f 1 0 ~ ° mm.  instrument.  from  the s e l e c t o r - a n a l y z e r  O - r i n g s were u s e d  A dual  o f two d i f f e r e n t i a l l y  t h e mass s p e c t r o m e t e r and  pump b a c k e d  A background  obtained.  multiplier,  f o rthis  chapter.  was e a s i l y  obtained.  instrument w i l l  The  be d e t a i l e d  79  1  ,  1  0  0.1  0.1  E L E C T R O N E N E R G Y DS ITRB I UTO I N (VOLTS) Figure  7,  An E l e c t r o n  Energy  Distribution,  RESIDUAL MASS SPECTRUM  28  81  3.3.3  The Quadrupole The  distillation instruments  quadrupole of  the  total  were  identical  except  was g o l d  steel,  different.  for  The g r i d s  tungsten  grid  supports  This  procedure  were  features  rebuilt  wire  plated  were  a very  steel  similar  to  rigid  0.002"  screwed  304  was gold  described to  ionization  the  apparatus.  double-layer  slit  details  of the type  those  the  Firstly,  construction  were  total  entrance  i o n chamber  grid.  and f i l a m e n t  was i d e n t i c a l  described  f o r the monopole  block  electron  exit  The  spectrometer  the  Associates  mass  the one s u p p l i e d  supplied  as  replaced  an i n t e g r a l by a  Ultek  with  o f t h e Quad  instrument.  aperture  Incorporated,  modification  was  features.  the grid  f o r the  were  constructional  i n place  frames  used  housing  included. The  was  and the  formed by w i n d i n g  and these  of those  The dimensions  brass  on frames  produced mild  to be a  o f t h e two  versions  f o r two i m p o r t a n t  described  plated  model,  and s e c o n d l y ,  the monopole,  A gold  favourable  were  i n the previous  material  plated  was i n t e n d e d  i o n i z a t i o n apparatus.  as  stainless  instrument  described.  selectors  same  the  t h e most  previously  The in  Instrument  this 250  part  14-stage  was  i n design  The movable  250.  instrument.  was t h a t  slit  to  the  Electronics  The i o n gun u s e d The o n l y electron  o f the quadrupole head  EMI 9 6 0 3  that  included.  e m p l o y e d was a n Quad  to  multiplier assembly  beryllium-copper multiplier.  82  The used  for  longer of  5  the  vacuum total  10~  mm.  7  to  1  x  routinely 10"  that  A.  8  quoted  3.3.4  by  T he for  the  1.5V.  is  or  (except  22.4V. for  performance  of  the  in  unit  Fig.  mercury  and  spread  driven  at  a  shunt-wound lead the  accumulator, filament  circuit  was  inelastic increased. a  motors.  separate  voltages  was used  22.5  were  was the  to  the  order  cells,  used  to  (see  to  the  were  10-turn  from  resistors  Beckmann  arranged small D . C .  9)  stepped  a  the  battery,  6V,, used  For  value  and  energy  to  amp-hour control  the  of  B8  was  supplied  the  ion or  be  This  was  a battery  to  80  resistor.  potential  either  electron  resistance  ion  either  were  measurements,  multi-tap  were  Fig.  instruments.  box  and  the  variable  inner-outer  potentials  control  was  three  the  variable  supply  on  was  500.  used  filament  wattage  approximately  supply  The the  mV.  selector, analyzer,  and  supply)  80  Equipment  by  supplied  no  and  m/e  speeds  all  was  spectrometer  The b a t t e r i e s  a high  V.  used  of  constant  and  initially  of  50  of  scattering The  mass  Ancillary  in  voltages  selection  it  resolution  and  9.  filament  The h e l i p o t s  energy  mass  which  helipots.  but  between  intensity  electrodes  the  of  an  Circuits  shown  one  vacuums  with  circuit  various  chamber  distributions  EAI;  Electronic  Residual  the  obtained.  obtained  The  was  apparatus,  baking.  Hg w e r e  Electron were  employed  ionization  subjected  x  system  a  from  gun regulated  I- i g u r e  9.  The  Selector-Analyzer  Electrical  Circuit.  84  D.C.  power  supply  connected  via  an  appropriate  resistor  chain. The monitored Model  in  200B  all  necessary  or  602  passed  by  analyzer  ionization  the  all  gave  two  instruments  the  vibrating  hence  could  necessary supplied power  signals, the  to  order  vibrating  measurements. current,  reed  was  it  this  a  triaxial  input.  current  electron was  two  the  with  ion  to  the  detect  replaced  For and  the  the  ion  Vibrating  detection was  in  by  Reed  the  a  Keithley  a  For  the  were the  latter  including  from ground  and  potentials Power  5kV.,  measurement  in  electron  system  ions.  Electrometer  the  positive  through  used  Cary  current  isolated  high  amplifier  being  the  instruments.  negative  reed  a  Electrometer  was  instruments, using  The  d i s t r i b u t i o n or  measured  Reed  This  other  vibrating  collector  When  with  electrometer  to  decade  Model  entire  transformer. the  appropriate  preliminary amplification). the  Instruments  Instruments  "floated"  the  the  and q u a d r u p o l e i n s t r u m e n t s ,  reed  be  in  made  Keithley  Keithley  (the  the  with  was  a  Vibrating  three  were  monopole  multiplier  in  a  chamber  by  current)  31  ion  by  electron  apparatus.  Electrometer  measurements  1:1  replaced  Model  the  current  the  Electrometer  In  (in  equipped  permit  scattering  in  instruments  record  was  Instruments  601  to  to  the  inelastic  total  three  shunt  electrometer 601  current  Electrometer  resistance was  electron  of  was  insulated positive  grounded.  ion  When  " f l o a t i n g " mode  85  of  operation,  reduced D.C,  to  the output  ground  converter  departmental  potential  which  monopole  oscillator power  mass  from by  positive  reversing  component  i o n to the  of  from  the monopole  automated.  Frequency D.C.  instrument Model  scaling  400  electron  runs  were  improve curve  thus  applied  o f the  energy  from  input  obtained  to  Model  scan  of the  scan  were  manually  noise  ratio  was p r i n t e d  the  of  Voltage  to  the  Vidar  i n the time  analyzer,  with  cumulative  final  o u t on p a p e r  sequence  and t h e  synchronized  analyzer the  reed  Chicago  several  the  data  completely  from  a Nuclear  operated  of  accomplished  by t h e D . C . t o  The output  Usually  D.C.  the D . C .  was  241-07  coupled  to  V.  the r o d .  of  sweep.  was  the v i b r a t i n g  ions.  i n t h e memory  signal  to  The  monopole  inverting  instruments  a Vidar  the  of the  and p r e s e n t i n g  Channel Analyzer  stored  the  and thus  drive  o f m/e = 1  ion transmission  T h e two w e r e  as  range  Conversion  signal  The r a t e  point  h a d a mass  150.  for negative  mode.  starting  3 0 1 C 0 •*• 1000  and q u a d r u p o l e  was u s e d  34-27  Model  was f e d i n t o  converter  to  by a F l u k e  of handling  Converter.  used  i n F i g , 10.  diode,  The output  electrometer  the  method  oscillator shown  the p o t e n t i a l  The  by t h e  is  negative  5690  D . C , to  and c o n s t r u c t e d  of the  The monopole m/e *  was  shop.  spectrometer  t o appr oximately  the instrument  by a 3 k V . , i n s u l a t e d  diagram  was p o w e r e d  supply.  from  was d e s i g n e d  electronics  A circuit the  signal  i n order data,  tape,  to  The and  this  .02/  -T-  220  1200  pf./ 6 0 0  V.  -©  OUTPUT  D C .  V. D C .  1 R F C  .10K/W10W. DC  O  TEST  2 EXT. S W E E P  5  .01  5 6 9 0  1KV.  o  6.3 V A C . .5G0K 2W.  o < 001  °  1KV. > 7 5 0 < >  6 0 K . / 4 W .  L1  6BK.  2W. 100  K.  10T H E L I P O T  -L.01  / 3KV.  R F C  6 M H Z . /  2 A .  <f  87  was  translated  was  a plot  b y a n IBM 7 0 4 4  of the  to  a Calcomp Type  in  the next  If  it  Keithley  chapter  are  601  the  or  602  IBM 7 0 4 4  current  for  variations is  to  shown  Method  Electrometer,  i n the  a l l three  same.  the  filament  (measured  was  adjusted  to  of  current slits grid  10"  less  A i  varied  a  was c o n n e c t e d  to  current  plot  A block  to  second, to  the  current In  the r a t i o  i n order  this  of the  correct  diagram  of  the  the method  of  operation  than  at  of  than  50yA.  was a d j u s t e d  This  give  current  The e n t i r e with  respect  output  the so  With slits,  was t y p i c a l l y system  the s e l e c t o r ,  from  selector)  accelerating f i l a m e n t and  that the the  a maximum c u r r e n t  analyzer to  of the An  between  of the s e l e c t o r to  the emission  slit  i n the i o n chamber.  was a d j u s t e d  i n voltage  less  voltage  the voltage  A.  the entrance  I V . was a p p l i e d  grid  collector.  a n d 10  a distribution,  at  a value  and the  voltage  electron  current,  the i o n current.  instruments,  To r e c o r d  was o b t a i n e d  set  plots.  i n F i g . 11.  the  slit,  with  latter.  shown  and the e l e c t r o n  was i n s t r u c t e d  was  the  system  graphs  computer  the electron  analyzer  the e l e c t r o n  these  coupled  of Operation In  voltage  record  of  result  IBM 7044  Marty o f t h e  examples  simultaneously  ion  system  to  The end  p r o d u c e d by the  Plotter,  multichannel  recorded  case,  3.4  565  was n e c e s s a r y  identical  was  curve  Computer,  a maximum analyzer analyzer at  between was  then  and t h e  the  ELECTRON IMPACT SPECTROMETER OUTPUT AND DATA RETRIEVAL SYSTEM  ELECTRON MONOCHROMATOR AND ION SOURCE  ELECTRON MULTIPLIER EMI 9603  MASS FILTER  CHART RECORDER  CARY MODEL 31 VIBRATING REED ELECTROMETER  m  VIDAR 241 VOLTAGE TO FREQUENCY CONVERTER PLOTTER  OSCILLOSCOPE  COMPUTER  TAPE PUNCH  TYPEWRITER  MULTICHANNEL ANALYSER NUCLEAR CHICAGO 34-27  89  current  to  of  voltage  this  scan).  the  In  electron  the  (see  and  near  +50  V.  grid  construction  than  analyzer (with  the  the  respect  to  used  the  and  the  primary  beam.  the  exit  the  analyzer  slit  potential  of  electron  function  to  be  detailed  were  the  total  as  function of  instruments,  plates).  at  the  operated The  ionization  operated  a  method  normally  slit  electron  of  ions,  The the  single  instrument  a potential  this  energy a  was  located  was  m a x i m i z e d by  and,  energies  ion  chamber  passed  the  of  less  varying  of  less  the  focussing  applied  entrance by  respect  to  slit  of the  the  was  of,  between  changing  analyzer  recorded  chamber  as  appropriate in  the ion  than  voltage  the  potentials energy  with 10  was  the  eV,,  by  selector.  recorded  maximizing  discussed to  the  and on  the  the the  ion ion  generally  quadrupole  were  often  above.  formation  instrument,  spectrometer,  particularly  by  maximum i n t e n s i t y  with  the  obtained  and by  decreased  were  gas  mass  total  the  were  as  potential.  ion  setting  the  The  by  curves  sample  with  50eV.,  and  analyzer  changing  to  curves  deccelerating  entire  current  at  give  the  and w i t h  eV.,  to  progressively  current  electrodes.  energy  was  of  electron  scattering  analyzer  Ionization  ion  in  electron  selector  50  the  recorded  and q u a d r u p o l e  inelastic  the  an  for  was  30V.  presetting  a  9  catchers  catchers  The  The  Fig.  monopole  selector  required  collector  the With of  desired current gun  kept  below  instrument,  employed.  The  ion  90  electron and  the  energy  in  terms were  when  of  obtained  equilibrium series  maintained  of  with  be  the  several  substances  weeks  until with  of  this  as  a broadening  of  of  a high  level  circumstances, performance instrument  was was  the  the  of  that  consistent  hot  the  running  day  in  after  to  be  the  d i s t r i b u t i o n or ion  restored. to  was  night.  usually  occurred  running  certain  manifested  as  the  curves.  instrument  Consequently,  particularly  was  Careful restore  either  these  replated, cleaning  the  bad  appearance  Under  was  curves  reached  and  or  deterioration  sufficient  and  instrument  performance  appeared  complete  had  filament.  planned,  the  results,  distribution,  The  on  range,  recorded.  instrument  the  desired  ionization efficiency  operation,  usually not  the  the  was  narrow  filament  in  noise  a  were  (hydrocarbons  respect).  curve  reproducible  runs  over  mentioned  Deterioration after  scanned  obtaining  obtaining  never  a  should  terms  of  thermal  then  ionization efficiency It  both  was  and of  the  performance.  CHAPTER RESULTS  4.1  Inelastic  4.1.1  Helium  obtained Fig.  from  12,  energy  The  of  50  diagram.  ionization  apparatus  eV.  total  The  units) as  to  a  the  Herzberg  superimposed background inelastic  obtained  diagram measured  function  on  a  energy  Another  outer  at  angle  with  were  solution  has  of  is  the  the  the  is  the  of  that the  0°  to  the  loss  of  the  in  indicated  on  of  has  helium  which ion  electrons  collector  analyzer. discussed  This by  electron  helium  spectrum  the  in  current  background.  electrons  was  shown  incident  of  levels  seen,  is  electron  diagram  walls  g>f h e l i u m  an  energy  rising  from  been  the  level  reaching  catcher  an  of  continuously  possibility  beam  the  structure  As  arose  using  shows  of  observed  collisions  possible  was  (109).  possibly  unscattered  a  the  A complete  by  the  spectruia  An i d e n t i f i c a t i o n  contributing  slits.  scattering  beam,  electrons.  given  inelastic  spectrum  arbitrary  incident  from  AND D I S C U S S I O N  Scattering  The  (in  IV  been  is The  had  suffered  chamber in  on  the  the  after  reflection  problem,  Schulz  the  (31).  and The  92  <  24  Figure  12.  The  I  I  I  _L_  23 22 21 20 ENERGY LOSS (VOLTS)  Inelastic  Scattering  Spectrum  of  Helium.  93  pressure micron  of helium  of  spectrum  by Simpson  conditions. except,  (2*p,  was a p p r o x i m a t e l y  i n excellent  needs  that  3*p,  is  and M i e l c z a r e k  Little  perhaps,  helium  instrument  1  mercury. The  obtained  i n the  4*p)  (49)  to be s a i d  the  optically  are  very  agreement using  about  the  this  allowed  prominent,  with  that  same  spectrum  transitions and t h a t  of  the  spin  3 forbidden  states  (2  under  stated  conditions.  the  spectrum papers and  has  already  o f Simpson  Raff  4.1.2  (50,  19.8  been  eV.) are  not s t r o n g l y  A discussion  given  of  i n Chapter  and M i e l c z a r e k  (49)  the helium  II,  and o f  excited  and i n the Kuppermann  51) .  Ethylene The  the  S at  total  ionization  experimental helium. band  Also  were  on t h e  of a Rydberg  (110).  scattering  apparatus  conditions  Indicated  heads  Tutte  inelastic  is  shown  t h e same  diagram  Series  indicated  spectrum  are  ethylene  i n F i g . 13.  as  those  from  The  employed  the p o s i t i o n s  observed  are  of  by P r i c e  two i o n i z a t i o n  of  for the  and potentials  (111). The by  Simpson  also  agrees  spectrum  compares  and M i e l c z a r e k in its  spectrum  obtained  incident  electrons.  (49)  overall  using  profile  by G e i g e r Both  very  well  t h e same  with  that  high  (112)  of workers  obtained  conditions.  a very  and Wittmaack  groups  with  have  It  resolution  using  33keV.  compared  94  o 10 II  LU  OJ  u  gure  13.  The  Inelastic  Scattering  Spectrum  of  Ethylene.  95  their  spectra  experiment and  with  at  (114)  due  these to  results  spectra.  the  angles  However,  the  is  i n some  13  peak  was a l s o of  the  (when  doubt  seen  Born  using  shape  the broad  Geiger  of  A p p r o x i m a t i o n at  high  an i n c i d e n t  the high  feature  peak  of  centered  i n the spectra  and W i t t m a a c k .  the second  Dibeler, at  (117)  found  curve  occurring  might  the  of  these  ionization  slightly curve  likely  50 e V . ) . curve  less of  by p h o t o e l e c t r o n  would  suggest  be e x p l a i n e d by t h e  that  The b r e a k argument  found  11.7  impact  found  show a n y of  potential.  ethylene.  has been  This  potential  than  The f a c t  eV.  spectra  (116)  eV.  shown i n  and M i e l c z a r e k  ionization  i n the electron  autoionization.  12  of Simpson  11.74  region  is  scattering  about  and R o s e n s t o c k  efficiency  a break  of  the spectrum  at  energy  due to  Walker  an e n e r g y  photoionization  be  at  energy  angle  at  None  indeed  this  impact  (115).  ethylene,  potential  Ross  differ  this  at  or  (50)  of helium,  structure  structure  (113).  electron  and R a f f  case  recognizable  Botter,  a similar  Kuppermann  interesting  Fig.  and  of  of  exact  An is  absorption  and Watanabe  obtained  As f o r t h e  failure  scattering  s t i l l  have  an o p t i c a l  200 e V .  The from  of  p e r f o r m e d by Z e l i k o f f  Lassettre  spectrum  the results  some  eV., in Also,  no  their  Collin  ionization  that  vague  efficiency  ionization  spectroscopy  in  this  structure  might  found  by C o l l i n  (117)  given  i n Sec.  2.3.3  96  regarding  the  possible  autoionizing  4.2  levels  Positive  4.2.1  in  electron  of  optically  impact  allowed  curves.  Ions  Helium The  facilitates a  behaviour  h e l i u m atom  the  considerable  potential,  study  of  energy  has  electronic  ionization  range  ionization  an  can  above  take  structure  threshold  the  place  first to  a  laws,  which  since  for  ionization  single  state  2 (  Sjy )  only.  2  indicated ion  by  A n RPD s t u d y  that  the  electron  studies showed  of a  threshold  impact  this  voltage  crude  estimate  no  Nevertheless, construction the of  those of  the  ion  fifty  curves The is  one shown  presented  in in  range.  for  the  in  total the  the  instrument the  of  energy.  curve  law  part  (118),  production  this  threshold  for  Fox  ionization  yield  in  by  excess  However,  necessary  for  Fig.  course  were  respect  chosen  in  monopole  the  curves  with  the  species  Early  apparatus over  study  a  was  c o u l d be  motivated which  this  somewhat made.  the  incorporated  accurate  measurement  yields.  During than  law  observations  sophistications relative  on  of  this  linear  curvature  considerable and  was  species  definite  of  to  of  recorded. their  The  Appendix II.  research The  overall  comparison  14.  the  with  The  reproducibility shape  the  numerical curve  on h e l i u m ,  was  for  this  s h o w n was  of  the  excellent.  theoretical  data  more  an  models curve  are  97  s u m judbmigyb Figure  14.  The  Ionization  'iN3yyno  NOI  E f f i c i e n c y Curve  of  Helium.  98  accumulation  of  four  The  pressure  of helium  and  the  electron  were  made  to  with  respect  Fig.  15  current that  to  gas  the  the  The  was  result  of the  An e n l a r g e d  experimental  curye  divided  ten " s l i c e s "  A planimeter and hence  their  curve  probability  law t o  energy  (referred  ionization the  results  were  experimental assuming  experimental the  curve  first  the  matched  ionization  the  the  energy  the  same the of  f u n c t i o n i n steps  electron  area  of  appropriate  the  the  were  The  sliced At  each  the  IBM 7 0 4 4 ,  fashion.  and  The  s u p e r i m p o s e d by  ion current  an e n e r g y  of helium.  these  ionization  of AE.  by t h e h i g h e s t  the  the  width  electrons.  was c o m p u t e d b y t h e  at  to  of  of the d i s t r i b u t i o n )  potential  scales  i n the  energy  and by moving  centered  current.  test.  by a s s u m i n g  detectable  linear  d i s t r i b u t i o n was  content  curves  tests  electron  was made  determine  was c a u s e d  d i s t r i b u t i o n being  above  to  of  summed i n t h e  the  was  corresponding  and t h e o r e t i c a l  that  the  pressure  This  Hg.,  Extensive  e V . FWHM)  each  strip  mm.  of  t h e peak  from each  A.  10"6  facsimile  relative  this  8  analyzer.  ion current  theory  be t e s t e d ,  to  10~  gas  was c o n s t r u c t e d  across  was 8 x  and t o  was p l o t t e d .  was u s e d  theoretical  distribution  0.054  c  x  pressure  (width  slices  1.2  the helium  distribution  AE.  system  comparison with  way.  into  i n the m u l t i c h a n n e l  i n the  ensure  shows  following  scans  i n the  energy  of  AE/2 volts  This  two c u r v e s .  slice  effectively  The i o n  currents  Figure  15.  Gas  Pressure  Test.  100  of  t h e two w e r e  threshold. of  data;  tape  The computer  at  i n this  the  at  l a w as case  greater  apparent  curves  there  lower  to  power  a  degree  first  to  would  the curve with  above  logarithmic  would  energy  shown  is  conclusions  First  t h e two region  power  was made  laws  of  law i n  agreement  to  f i t  with  i n the  with  no o n e p o w e r l a w  energy  case  As i s  t h e c u r v e was  that  is  good  d i d n o t meet  f o r power with  the  very  low e n e r g y  good  clear  T h e two  above  between  but this  in this  law (65)  paper  1.127  threshold.  An a t t e m p t  law (64)  Also  sets  the  (69).  a higher  the e n t i r e  threshold.  from  the f i t i s  the  Although  became  the  both  10 v o l t s  above  demand  comparison  t h e n=3/2  Several comparisons.  Clearly  over  at  disagreement  the curve,  and i t  normalization  volts  by Wannier  volts  c a n be o b t a i n e d  worse  The  some  to p l o t  derived  apparent,  five  above  f o r an assumed  normalized  than  the o v e r a l l  comparison  a plot  As i s  is  energy  analyzer.  predicted  of success.  generally f i t  being  the agreement.  laws  few v o l t s  1.2<n<1.3,  such  were  curve  improve  higher high  data  energies.  experimental  order  shows  potential.  energies  also  16  threshold  ionization  a preset  of the m u l t i c h a n n e l  Fig.  curves  at  was i n s t r u c t e d  the experimental  output  power  normalized  range.  shown  i n F i g . 17.  was c h o s e n  a comparison  A  with  to be  five  Temkin's  i n F i g . 18. c a n be drawn  of a l l , there  is  from  no a g r e e m e n t  these between  101  siiNin  Figure  jLUbunayB iN3yym s  16.  Comparison  of  1.127  Law  NOI  with Helium . R e s u l t s  102  s u m lyuyiiayb Fi ure 6  17.  Comparison  of  'iKGUdra  1.5  Law w i t h  NOI  Helium  Results.  103  siiNn Figure  lyuyirauu 18.  Comparison  'iN3uyn3  o f Temkin  Law  with  NOI Helium  Results.  104  this and  work  and the  by B a t e s  et,  by  Fox  (118).  on  the  three  that  a  a  a l ,  law m i g h t  energy  McGowan  63),  curve  electrostatic  curves there  of h e l i u m which was n e v e r  be a p p r o p r i a t e .  It  is  (119)  in a careful  to  close  ionization  a 127°  threshold  eV.) a  power  law f i t s  their  data,  within  e V , , of threshold  a higher  power  law i s  The  work  would  o f McGowan  tend  to  be.a  function  this  might  test  the  region must It  indicate of  be so  possible  This  that  the  electron  the  observed  curvature.  much  ionization momentum source,  higher  process  of this  the  threshold  Omidvar  and t h e Near  would  have  (65)  i f  the  effect  here might  out  on t h e / ,  ionization  energy  of  a.  between  to  some  of  threshold  concept  i o n must  to  this  the value transfer  well  that  low  but  2  leading  Wannier's  electron. the  is  3 _ a  of  o f momentum  the  correct)  incident  a l . ,  target  presented  be i n t e r e s t i n g  I(E)"(E-IP)  effect  indicated.  law i t s e l f  would  et,  and t h a t  has p o i n t e d  determination  energies is  (120) It  law i s  theoretical  incoming  at  the  by Temkin  the  (and  a n d t h e work  theoretically.  of helium. the  that  energy.  law p r o p o s e d  await  is  and C l a r k e  over  that  of the  using to  the  fit  note  study  atom  indication  ((E-IP)<0.4 0.05  1.13  that  any  observed were run  the best  interesting  find  (61)  Certainly  provides  f o r the hydrogen  selector  by G e l t m a n  and e x p e r i m e n t a l l y  by Wannier  range.  and C l a r k e  efficiency  (62,  instruments,  law p r e d i c t e d  wide  law p r e d i c t e d  In a l l t h e  linear  1.127  linear  of  absorb  F o r an a t o m i c of directing  the  the  full  beam  the  ions  105  away  from  the  lead  to  variable  of  a  electron  with  an  ion  source ion  energy.  effusive  entrance  collection  The  gas  aperture,  effect  source  of  and h e n c e  efficiency  should the  not  type  as  be  a  function  too  used  in  would  serious  this  experiment. As interest with  in  was  mentioned  comparing  experiment.  compared  with  Thus,  the  the  formulas  of  The  formulas  used  Chapter  II,  comparison have  been  energy the  35  although being  it  made  the  curve  with  doubly  isotope  seen  must  The of  for  be  * of of  Fig.  ratio  =  and  experimental The  the  of  been by  been  Bartky  given  (72).  theoretical at  agreement curve  (73). in The  curves  an  between  is  comparison  remarkable, is  not  sections.  helium this  1^*  have  results  experimental that  calculations  and Thomson  have  and  some  predicted  (77)  A l l three  efficiency  from r e s i d u a l  instrument  Drawin  cross  employed i n  He  sections  eV.  is  helium  19.  the  ion  for  Bauer  10.5  there  classical  from  stressed  charged  as  cross  II,  calculations  the  absolute  4  monopole  in  ionization  He was  interference  charge  taken  of  results  these  eV.(E-IP)  Gryzinski  the  Gryzinski*(75),  n o r m a l i z e d to  of  Chapter  results  ionization  and were is  the  in  curve was  work  which  for  also  to has  the  studied.  avoid the  production The  any  same  mass  to  ++ .  The  curve  obtained  for  the  production of  from ^He  + +  the is  shown  I s h o u l d l i k e t o e x p r e s s my g r a t i t u d e t o D r . R . G o l d s t e i n the J e t P r o p u l s i o n L a b o r a t o r y f o r p o i n t i n g out the agreement the h e l i u m r e s u l t s with the c a l c u l a t i o n s of G r y z i n s k i .  106  SI •X. .  cV.  10  -SI ro o '4*.. oV O  >  0)  >o o cc TO UJ z  °\  \v  o >, o  UJ  \  .00 "CVJ  z o cc ro UJ  _l  UJ  O  h  (0  Z_ ^  (L) •I  I  T  Figure  z 5  LUN | DL>- < X C CC  O  : + O *+ O  • •  lilOQh  1  19.  *  1—  I  •cvi  1  1  1  1  1  r  (siiNn Advdiiaav) ±N3aano NOI Comparison of C l a s s i c a l lie 1 ium R e s u l t s .  Calculations  with  He + €—He+3€ 3  3  +  • EXPERIMENTAL — SQUARE LAW  W^i j * ' 70  \M ^i^^t^*fA*^' a  1  1  75 "  ^"  i  I  I  I  I  80 I  1  •  i  85  • •  »  • i  90  .  .  .  .  i  95  UNCORRECTED ELECTRON ENERGY (eV)  100  105  108  in  Fig.  in  the  of  this  the  20.  This  multichannel curve  result  is  of It  and  Wannier  for  double  the  those  of  Fox  mentioned have  low in  (121)  and  the  however signal  to  a  high.  This  was  abundance  of  2.3.1  this  that  a quadratic with  among  the  theoretical,  detailed  noise  eight  noise  comparison  agreement  of  to  predicted The  signal  Sec.  The  ratio partially ion.  Geltman  (61)  threshold theory  present  predictions  comparison  scans  is  law  is results, is  most  impossible with  ratio.  Nitrogen The  of  The  20.  satisfactory, present  accumulation  particularly  ionization.  Fig.  an  extremely  (88)  in  4.2.2  was  analyzer.  not  was  shown  the  curve  nitrogen  electron such  formation  has  been  impact  studies  techniques  ionization efficiency  the  autoionization  from  the  is  direct  a  nitrogen  since  The  One o f  the  electronically  interest,  s t u d i e d by  (122).  it by  seems  monopole  curve to  a  the  ion  of  discovered  occurring  the  ion.  below  This  considerable  demonstration  (83,  of  123).  curve  shown  earliest  He  attracted  efficiency  of  the .  of  positive  monoenergetic  curve  clear  impact  is  (25)  state  has  be  instrument  reproduction  Clarke  excited  electron  ionization  by  charged  performed  the  of  singly  was  in  feature  the  extensively  structure first  of  in  plotter  for Fig.  output  nitrogen 21. of  obtained  (Fig. the  21  109  siiNin AyuynayH *iN3yyno Figure  21.  The  Ionization  E f f i c i e n c y Curve  NOI for  Nitrogen.  110  s i i N n Ayuynayu i N 3 y y n 3 !  Figure  22.  Autoionization  in  Nitrogen.  NOI  Ill  IBM  7044  scale  computer  shown  as  discussed  was n o t c o r r e c t e d  The  curve  shows  18  e V . , (uncorrected)  to  the  B Iu*  threshold is  (58).  clearly  a more  scale  of  Fig.  the  i n the  F i g . 22  is  energy scan  the  ionization  autoionization  correspond  region this  above  the  with  near  break  near  to , i o n i z a t i o n  16  region.  ionization autoionization  eV.  F i g . 22  (The  and d i f f e r s  i n the  literature  here.  However,  of  this  thesis  should  curve  to  efficiency  structure  said  energy  from  that  shown  have  (118,  the points  be b o r n e  been  122,  124),  when  data  of  nitrogen,  discussed  mentioned  i n mind  photoionization  curve  little  will  i n Sec.  2.3.3  comparing  the  (83).  Oxygen The  monopole Fig.  23.  contact  The c u r v e  is  curve  obtained  molecule  was t h e  of a single  with  result  The energy  etc.  positions  labelled  efficiency  f o r the oxygen  analyzer.  potentials,  assigned  break  ionization  instrument  multichannel  the  of  f o r a shallow  eV. ,  energy  potentials.  associated  uncorrected,  be  4.2.3  3.22  The  21.)  extensively  nitrogen  would  situated  detailed  Since and  evidence  which  3.3.4).  for contact  The s t r u c t u r e  seen  shows  in  state  2  i n Sec.  of the  scale  is  the  shown i n scan  i n the  was u n c o r r e c t e d  The arrows  on t h e d i a g r a m  the breaks  i n the  spectroscopic  from  curve.  symbol  for  mark Each  giving  the  1 12  ( s u m Advanaav) INSIPID NOI  Figure  23.  The  Ionization hfficiency  Curve  for  Oxygen^  113  state  in  vertical  which  the  lines  above  (relative  to  ionization (125). seen for  from  species  of  the  (21, in  32, two  127,  states  impact  seem  to  have  measurements  that  this for  the  energy the  impact  A •  (32,  curve  the  measurements  can  also  energy  curve  curves  using  techniques  presented  is  here 2  as  a  £  here, variety  excellent is  ,  interesting  near  p r e v i o u s l y by  ^ state however,  be  obtained  workers  detected 1  ion  the  (126).  indicated  2  of  spectroscopic  Gilmore  The  positions  potential)  other  (126),  and  region,  mark  the  potential  impact  been  formed.  is  well  20  electron  known  Gilmore  has  eV.,  from  pointed  2  observed  question  by  The  2 out  by  state  measurements.  optical  of  be  oxygen  between  The The  the  set  electron  128).  mark  from  of  obtained  respects.  d oes not  known  prepared  monoenergetic  to  ionization  agreement  curves  thought curve  excellent  The and  first  known  the  is  the  potentials  The  this  the  ion  There  and  break.  has  127,  *  been 128),  is  u  states these The  are  could state  observed but  its  structure  expected well  be  labelled  to  in  the  is  curve  in  responsible with  p r e v i o u s l y by identity  lie  a  electron  unknown. below  the  4  II  u state  which  existence is  seen  (130)  of  from  among  Morrison  and  can  be  associated  with  autoionizing states the  photon  others,  impact  Peresse  Nicholson  (93)  in  data  autoionization. this of  and T u f f i n and  McGowan  energy  Cook  and  (131), et.  al,  The  region Metzger Dorman, (132)  114  have the  pointed electron  again, in  4.3  out  the  mind  impact  points  when  Negative  4.3.1  0"  designated:  by  the  The  energy  ion  sum  of  SF .  peak  6  was  this  error  SF^  0  of  error e  was  V.  in  ^0.1  is  (94).  curve.  should  to  Once  be  kept  autoionization.  shown in  at  extensively  for It  is  of  the  This  majority  of  fashion  eV.  It  is  in  assigning a  from  curve  analyzer.  mixture of  of  the  0  2  considering  the  an  that  the  negative  the  have  possible  been  calibration  that  would  for  a  by  (7).  has  This  peak  assigned  the  obtained  24.  running  estimated  4.3.5  work  curve  Fig.  this  Sec.  this  by  multichannel  by  was  the  of  in  the  0- e V .  (hereafter  2  The  position  involved See  0  studied  process  work.  random  from  calibrated  adopted  calibrated  at  of  al.  energy  scales  be  source  bibliography  scans  capture  SF "  systematic  2,3.3  been  et.  was  The  6  in  has  eight  scale  procedure  efficiency  Sec.  produced  instrument  dissociative  studied  0"  Compton  was  the  the  A partial  monopole  that  in  autoionization  Oxygen  2  the  and  raised  0~/0 )  RPD m e t h o d .  2  ionization  of  Ions  The  0  contribution  assessing  From  compiled  the  energy average  there  SF^"  discussion  ions  is  peak of  a to  the  peak. The  maximum  cross  section  for  the  production  of  115  O  LO  CD  ID CO CO  CO  LO CM  1  —'  >— ^  CC  UJ o c\) L U  LO  O CC LU  -i  UJ  LO  s u m ji.yyyiiayb •j.Niyyra NOI Figure  24.  The  Formation  of  0  from  Oxygen.  1 16  O'/C^  occurs  at  6.6  of  other  is  difficult  to  tail  slightly  to  be  said  that  appearance  to  4.1  which of  workers  e V . , i n good  eV,  specify  the This  range  3.75  to  (133-136).  value  between  Frost  and McDowell  curve  appropriate  capture  i n Sec. At  known  onset  of  as  i f  20.3  there  4.3.2  is  process  U  From The  o f 0  this  less  most  A very  by Randolph presented  than  or  equal values  low v a l u e  and G e b a l l e  by a  of negative  tends can  a potential  o f 0"  0"  it  literature  (94).  as  0"/C>2 (128).  being  signal  the d i s s o c i a t i v e appearance  a second  e V . , leading  second  type  process  process  of  eV.  formation  energies,  background  above  assignment  the  have  than  of  t h e peak  However,  is  results  potential  since  side.  the  (137).  energy  dissociative  i o n f o r m a t i o n was  2.4.1.  higher  this  lower  reported  This  ion pair  unexplained region  to  curve,  potential  and 4 . 9  (128)  mechanism.  discussed  well  4.3  e V . , has been  the  low e n e r g y  is  with  The appearance-  from  the  agreement  to  which  F i g . 24  shows  the  17.5  eV.  is  capture  present process  potential  process  found  via a  approximately  with  the p r o d u c t i o n  has been  can be formed  o f 0"  by o t h e r  i n the makes  difficult.  an o n s e t  An  of  the It  appears  approximately  ions.  workers  energy  This (128,  134).  Carbon Monoxide ionization  f r o m CO i s  efficiency  curve  shown i n F i g . 2 5 .  This  f o r the curve  production  was  obtained  siiNn Aybungyu 'iN3yyno Figure  25.  T h e Formation  of 0  from  Carbon  NOI Monoxide  118  on  the  quadrupole  calibrated  instrument,  against  SF."  and  the  formation.  energy The  scale  curve  was  was  the  6  result  of  five The  dissociative  scans  in  position  the of  multichannel  the  capture  is  10.4  appearance  potential  of  the  are  than  higher  (133,  136,  138),  and  the  and  Petrocelli  and  an  capture slightly  fairly for  negative This The  the  ion  state  of  corresponds appearance  dissociation have the  determined at  the  that  limit  of  this has  that  the  appearance  the  0"  of  a  ions  potential.  previous been  peak  9.4  values  studies near  10.1  eV.  Fineman  energy  the  of  eV.,  10,94  eV.,  of  peak  Fig.  25  shows  side.  This  is  dissociative 0"  Reference  0^.  being  for  would  that  formed  to  Lozier have  no  and This  24  is  2  the  is in  is  Fig.  same  peak  that  the  attractive. Fig.  correspond Rapp  CO  indicates  formed  detail. by  from  0"/0  illustrated  some  confirmed  These  eV.  CO" s t a t e . in  eV.  near  that  0?C0  to  approximate  has  been  situation  point  been  most  capture  CO w h i c h  the  9.6  formation  in  energy  potential  discussed situation  to  is  9,5  the  However, low  the  value  has  of  dissociative  sharp  and  measured  to  from  a  by  mentioned  leading  symmetric.  CO h a s  have  corresponding  ion  peak  potential  different  that  the  s h o u l d be  process  0"  potential  (139)  appearance  eV.,  produced  where  appearance  It  shows  those  peak  analyzer.  to  lb. the  Briglia  (136)  assessment  (140), kinetic  who energy  of  119  The pair the of  process exact  with  0~  of  the  sum o f  energy  curve  formation  the  o f 0~ f r o m  from  occurs  at  found  peak  are  of  2.1  N 0 is 2  that  since  energy  2  eV.  (136).  These  shown  to  this the  analyzer. to  6  are  is  Schulz  of  the  a n d by C u r r a n  the peaks  the width  of  f o r the  eV.  were the  not  is  6  showed  agreement  (142)  that  It  The  and Fox  (141)  resolved  to the  appears  region.  to  i n the  used  and  resonance  difficult  resolved  S F " peak  curve  in this  partially  It  cross  interesting.  by S c h u l z  show  the  i n good  peaks  clearly  The  SF ~ formation.  two o v e r l a p p i n g (142)  I t was  e V . , and t h e peak  The assymmetry  0.7 a n d 2 . 2  scale  i n F i g . 26.  (141),  side  instrument  the diagram,  values  and Fox  low e n e r g y  RPD m e t h o d at  07N 0 i s 0.  by C u r r a n  on t h e  obtained  fact  (139)  eV., for  correspond  i n the multichannel  potential  maxima  Again,  because  the quadrupole  from  the  eV.  Oxide  seen  there  20.92  does  can be c l e a r l y  capture  work,  it  of  As  and B r i g l i a  the  that  21.3  the i o n  and P e t r o c e l l i  respect  Rapp  with  Fineman  potential  is  difficult  with  those  using  is  was c a l i b r a t e d  with  curves  energy  scale  section  i f  approximately  signal.  obtained  two s c a n s  appearance  as  this  confirmed  Nitrous  The the  at  o n F i g . 25  an i o n p a i r .  From  for  of  of note  an a p p e a r a n c e  and have  formation  4.3.3  an o n s e t  background  measured  process,  feature  assignment  a rising  have  second  peaks  explain  present  calibrate resolution  120  SUNR Figure  Ayyyuayu 'iNByyra N O I 26,  The Formation  of 0  from  Nitrous  Oxide.  121  was  more  RPD  than  adequate  to  resolve  some  but  potential  4.3.4  it  to  was  and  systems  were  portions  formation  impossible  hoped  at  one  the  hydrogen h a l i d e  this  not  was  showing  the  27,  the  sensitivity  Electrometer  was  increased  against the  SF^,  fairly  the  of  from  of  the  curve  an  ion  the  show pair  appearance  rather, the  and  the  work  for  this  formation  in  all  the  molecules.  However,  as  the  sample  of  by  a  for  the  electron this  energy  the  ion  to  of  Br"  is  this of  current method scale  from  this  shown  in  of  to of  ion  be  calibrated  determined chamber.  calibration  could well  in  was error  eV. Nevertheless,  it  appears  as  if  27.  approximately  not  was  the  Fig.  at  was  energy  process,  Reed  33.3  curve  results  B ^ .  for  Vibrating  factor  corrosive  preliminary  curve  the  zero  handle  Some  instrument  scale  instrument,  crude,  0.2+0.4  monopole  energy  but  cutoff  monopole  stage  ionization efficiency  The  this  estimate  formation  (In  eV.).  0"  abandoned.  from  Fig.  to  of  o r i g i n a l l y designed  program  obtained  of  negative  obtained  by  in  Bromine  was  The  the  seen  occurrence.  investigate  halogen  gases,  energy  the  this  Prom It  thesis  for  for  Br"  were  higher  evidence  process,  by  peaks  studies. The  1.4  the  Br"/Br2  has  an  In  S1INR' JLUUU1IGUU 'INBUUfD NO I Figure  27.  T h e Formation  o f B r " From  Bromine.  123  appearance peak 130  is  potential  extremely  seen,  as  is  capture a third  The results  of  single  process  arising  from  Because  of  (3.36 lies  inherent  very  the h i g h  electron  e V . ) the d i s s o c i a t i o n well  below  the  zero  and the  neutral  potential  energy  This  results  potential  would  energy  below  could  correspond  spin  The  third  must  very  energy  of  curve the  Br" which  The d i s s o c i a t i o n to  the  splitting broad  be a s s o c i a t e d  formation  another  with  v=0  (143)  of B r  Br  (  " .  2  of  atom curve  level  of the  is  atom  a  is  peak  second  a  curve n  d  B  0.46 at  r  "  (  eV.  1  s  to  ) •  (144).  3,3 e V . ,  B r ~ tending 2  peak.  neutral  this  P j ^ )  the  capture  the  of 2  as  cross  there  capture  state  dissociative  neutral  initial  limit  a  peak  could  crosses  eV.  a maximum  The  the  that  of  found  repulsive  curve  i n the bromine  dissociative  with  of  narrow  of  authors  curve  3.3  t h e RPD  authors  this  the  indicate  from  clearly  at  of the bromine  energy  at  e V . , is  centered  peak.  affinity  the  f o r a second  a repulsive  limit  0.9  peak  by t h e s e  here  curve  1 eV.  orbit  These  repulsive  explain  presented  curve  The  (143).  point  molecule,  latter.  differ  was i l l u s t r a t e d to  at  here  f o r any h i g h e r  of  broader  peak  capture  capture  height  due to  somewhat  was no e v i d e n c e  a transition  half  a maximum  presented  There  at  low i n t e n s i t y  bromine  The  with  dissociative  broadening  A second,  dissociative  eV.  capture  The f i r s t a width  and McDowell  assymetric  1 e V . , or  with  peak  results  Frost  0.03±0.03  below  the  distribution.  dissociative  at  sharp,  mV., including  electron  of O.eV.  124  one  of  these  two  Frost ionization ion in  pair  in  process. at  of  has that  to  workers  peaks  are  The  widths  of  the  diagrams.  are  greater  measured  this  formed  the from  slight  eV. ,  in  low,  curve  However,  and  energy  an  rise  the  process.  As  the  from in  no  the  detailed  region.  would  be  of  introducing  of  energy  scales  has  of  at  28  half  seen,  the  expected  in  the  most  from  both SF " 6  are of  by  the  nonor  many Typical  quadrupole  indicated the  SF^  width  the  cases,  error  in  respectively.  the  peak  9).  the  29  width  measured  of  (7,  and  and  at  confirmed  height  a systematic for  been  times  resonant  occurring  monopole  distributions  The w i d t h  a highly  process  Figures  be  several  RPD t e c h n i q u e  the  peaks  can  in  This  d i s t r i b u t i o n was,  effect  mentioned  capture  using  these  energy  is  energy.  shown  than  millivolts.  the  in  SF^"  obtained  instrument  electron  this  arising the  10  extremely  been  zero  SF^"  to  measured  2  that  than  already  very  by  was  attempted  electron  times  Br"/Br  possible  greater  signal  dissociative near  is  for  also  Hexafluoride  It thesis  It  limits. (143)  corresponds  were  Sulfur  this  27 the  measurements  curve  energies  Fig.  intensity  4.3.5  and M c D o w e l l  efficiency  current  shown  dissociation  into  negative  peaks  of  the  analyzer.  less  might  on  than  have the ions  This  100  the calibration studied  in  125  ZD >CO cc CO  SFg (  M O N O P O L E )  F W H M  CD CO cu  : 1 6 0 mV.  UJ  co  CO  ZD  r *• -.8  i  -..ll  ELECTRON Figure  28 .  L  Peak  -.0  ENERGY, from  the Monopole  .4  VOLTS Instrument.  .8  r  S F  6  ( Q U A D R U P O L E )  FWHM  -.8  =150 mV,  -.4  -.0  .4  .8  ELECTRON ENERGY, VQLTS gu r e  29.  SF  Peak  from  the  Quadrupole  Instrument.  127  this  work,  and f o r a l l t h e s c a v e n g i n g This  be  explained  SF, o is  does most  apparent  broadening  of  t h e S F ^ " peak  i n a number  of ways.  It  is  indeed  unlikely  have  a measureable  i n view  could  of the  broadening  the  electron  energy  The  electron  d i s t r i b u t i o n , measured  always  determined  in  i o n chamber.  dropped the  with  distributions of the  be  case  the  ionization  at  were  such  there  the  electron  as  to  that  of  examined a  with SF  formation  i n this  work,  low i n t e n s i t y the  ~/SF  were  It  is  energies. was  were  analyzer  not  any e n e r g y .  a  (119).  three  F"  It  conditions by t h e  and S F " from 5  The peak of  of Curran  in substantial  dependent  f o r F"/SF^  agreement  as  or  i f  been noted  cause  a  analyzer. S F ^ were was o b s e r v e d in  The r e s u l t s with  would  inner  has  s h o u l d be  the S F ^ " peak, (145).  true  the  i n the  would  that  This  into  conditions  angle  5 eV.,  possible  were  (7).  of  least  by the  analyzer at  low  at  this  and Fox  analyzer  of  the  but  a non-uniform potential,  facsimile  observation 6  of  the  penetrations  and C l a r k e  latter  very  energy  i n the d i s t r i b u t i o n measured The  be  with  the surface  distribution  these  field  produce  b y McGowan  change  were  at  energies.  by t h e  that  width,  o f Hickam  detected  distribution  i f  mentioned none  lower  could  by a r e l a x a t i o n  (15)  an e l e c t r o n  measured  chamber,  box  caused  The c u r r e n t  actual  i f  been  distribution  drastically  sample  have  possible  inherent  claims  The  the  results.  to  agreement for  previous  128  measurements  4.3.6  (7,  9).  C l " From C a r b o n The  for  the  This and  curve  formation  curve the  was  figure  obtained  of  not is  Tetrachloride  C l " from  obtained a  direct  sensitivity  of  the  Vibrating  by  of  300  at  energy  scale  for  CCl^ is  trace  recorder.  factor  the  using  potentiometric  a  from  As  the from  monopole  instrument  shown  Fig.  energies  analyzer,  the  a  chart  on  the  of  diagram,  Electrometer  greater  this  curve  was  C1"/CC1^ i s  first  formed  30.  multichannel  indicated Reed  in  than  calibrated  was  2.6  the  increased  eV.  against  The SF^"  formation.  dissociative (FWHM) Thus, of  of  the  this  SF^.  capture  At but  is  A less peak  energy  is  past  at  virtually  intense,  and  centered  at  and  energies  threshold  O.eV.  capture  somewhat eV.  the  scan  this  has  a maximum  there for  is  this  a  peak  to  broader  third,  evidence process  the  On t h e  of  is  resonant  The measured  identical  0.8  a highly  at  is  width  110  mV.  capture  peak  dissociative  higher  very  broad  capture  approximately  for  an  ion  obscured  pair by  the  6  eV.  process, lower  structure. There  the  is  process  dissociative  portion  seen,  higher the  first  peak  sensitivity peak  capture  from  (146  -  have  been  151).,  but  numerous there  studies  has  been  of  C1"/CC1^  little  in  agreement  129  O I N CURRENT (ARBTIRARY UNITS)  Figure  30.  The  Formation  of  Cl  from  Carbon  Tetrachloride.  130  on  the  exact  on  the  relative  peaks.  peak  varied  this  to  heights  study  of  work,  9.6  the  i o n source  F ox  and C u r r a n current  varied.  first  of the height  t h e peak  to  0.9  seems  found  at  The r a t i o  (1.50)  can change  a similar  experiment,  in  on  demonstrated while  when t h e  (and the d i s t r i b u t i o n i n t h e i r  For the p r e s e n t  found  the r a t i o ,  effect  zero  0.8 e V . ,  t o be dependent  and Berg  capture  of the  shown h e r e  (148).  Hickam  centers  two d i s s o c i a t i v e  ratio  temperature  (147)  The disagreement  of  The r a t i o  conditions.  the  the  (147)  was 2 1 .  that  electron  curve.  the height  from  experimental  was  of the  In previous  energy has  shape  experiment)  the electron  current  - 8 was  2 x  10  A . , the d i s t r i b u t i o n measured  was  50  the  results  the  peak  m V . , and t h e sample of  Fox and C u r r a n  heights  high  resolution  very  high  in  the  electron variation  seen  possibly second these  greatest  used  here  the  currents  as  third  (0.8  eV.) peak,  experiments  are  the  ratio  explanation were  A . , were  of The  of the performed  tetrachloride  9  From  wherein  used.  Little  noted. peak  p r e v i o u s l y by Reese et.  mm. H g .  resolution.  experiments  10~  analyzer  10"^  that  the highest  a possible  1 x  capture  by Marriott  seen  on c a r b o n  l o w as was  was 2 x  is  Several  study  i n the r a t i o  it at  is  ratio.  of  The been  is  measured  course  pressure  by t h e  a l .  et.  at  a l .  (148).  the r e l a t i v e in violent  approximately (149)  at  5.6  6  e V . , has e V . , and  As was t h e c a s e intensities  disagreement.  f o r the  measured  in  131  The seen  in  lower  Fig.  ion 30.  energies  pair  However,  than  workers  measured  the  as  being  approximately  in  this  ions 11.65  the  eV.  is  above  9  eV.,  current  mechanism, is  opened  11.5 of  this  eV., these  or near are  is  9  of  11.47 to  arising  The  and  an  of  by  a  the  the  results  of  al.(149),  for  have  formation  onset  observed  all  have positive  ionization  below  a positive  ion  pair  current  ion  contribution  Either  scavenging  attachment  above  the  observed  process.  secondary  of  much  photoionization.  currents sum  clearly  at  pair  the  dissociative  ion  the  ion  found  ion  from  broad  presumably  processes  to  et.  curve  eV. ,  the  is  Curran.(147)  (152)  ascribe  work  eV.  and  evidence  Watanabe  another  for  whereas  Fox  no  when  Reese  efficiency  found  impossible in  eV. ,  eV.  ionization  potential  it  13  ClVCCl^  commences  expected  potential  9  Similarly,  Thus,  ion  below  C C l ^ and  appearance  the  is  be  for  process  considered.  appearance  work  from  are  process  the  would  previous  measured  type  channel  approximately  contribution of  type  the  ion  of  one  pair  proces s.  4.3.7  The  Methyl The  iodo-,  bromo-,  work.  As  in  these  far  Halides  formation and as  the  halogen  chloromethane  could  molecules  of  has  be not  has  determined, been  negative  been  studied  negative  studied  by  ions  ion  from  in  this  formation  monoenergetic  132  electron  impact  resolution listed most  techniques,  studies  i n a review  recent  Dibeler  literature.  article  by C r a g g s  appear  The  are  formed  appearance  zero  volts"  that with  that  leading  to  the  only  (155).  the  molecules.  contributing  studies  low  are  (153).  o f Cox (154)  authors,  these  formed  formation  in and  of  was i n d e e d  structure  three  latter  potential  considerable the  several  and Massey  by d i s s o c i a t i v e  was o n l y  there  These  be t h o s e  By c o n t r a s t ,  an a p p e a r a n c e  found  to  potentials  Cl'/CHjCl  to  are  The  and o f  (155).  According I'/CHjI  there  i n the  studies  and Reese  although  ions- are  from 10  Cl'/CH^Cl.  above the  "very  an i o n p a i r eV.  determination to  process however,  mechanism  Cox f o u n d capture  of the  b e o f some  to  found  capture  the d i s s o c i a t i v e  seems  near  Cox ( 1 5 4 ) ,  Also,  and  processes.  and Reese  a dissociative  of  processes  capture  Dibeler  near  Br~/CH^Br  peaks  curve  interest  shapes (153,  156) .  4.3.8  I"  From M e t h y l The  for  the  The  curve  formation was t h e  analyzer. SF' "(m/e 5  was  not  curve  Because =  127)  Iodide obtained  of  I"  of  the  and I"(m/e  calibrated  the quadrupole  from CH^I i s  result of  from  against  three  shown  scans  interference =  127),  SF " . 6  instrument  i n F i g . 31.  i n the multichannel between  the energy Rather,  scale  the p r e v i o u s l y  133  CO h — _ l C D  CC UJ LU D  LU LU  s i i N r i Jiyuyiiayu Figure  31.  The  Formation  iN3uuno N Q I .  6  of  i "  from  Methyl  Iodide,  134  described  electron  calibration  of  In  the  Fig.  31,  was  increased  1.9  eV.  The  Pressure  =  the  by  to  1.5  x  the  the  360  capture Cox  is  these  has  work.  capture  Both  Cox  peak,  completely found Fig.  31  Tsuda, results  at  but  the  energies  greater  for  curve  current  «= 5  x  in  in  SF  by  and  6  excess  to  Henglein  and  explain  curves  reproducible  in  the  of  dissociative (155),  energies  the  position  light  by  of  none  by of  The  the  of  of  previous  found dissociative  authors  and  structure  series  greater  (8)  these  Dibeler  a  be  widths  The  and Hengleitn  energy' s t r u c t u r e .  capture  beam.  in  appearance.  9  to  although  at  obtained  10" A.  measured  Reese  (8),  current  the  of  and C C I 4 .  Dibeler  ion  appears  (FWHM)- was  than  were:  which  peak  Reese shown  runs  were (155) in  performed  apart.  Melton for  and  the  Hamill  (157)  formation  of  have CH,  +  eV.  Electrometer  of  above  in  Reed  this  the  0.2+0,4  potential  and J a c o b s  energies  by  a dissociative  the  (154)  quite  days  Vibrating  Thus,  in  seen  in  different  was  error  electron  greatly  difficult  no h i g h e r  several  RPD  rise  is  at  in  employed a monoenergetic  eV.,  ionization  33.3  capture  Jacobs  used.  formed  peaks  been  and by  workers  7  is  the  conditions  first  the  This  The than  of  capture  peak  (154)  of  was  may b e  of  mm. H g ;  5  appearance  mV.  initial  factor  10~  method  scale  experimental  The w i d t h  be  energy  a  3  O.eV.  cutoff  sensitivity  I"/CH I process,  beam  interpreted  from C H . I to  their suggest  135  that  there  methyl the  is  an  ion  pair  process  iodide  at  9.1  eV. ,  although  cross  molecule is  than  suggested  above  9  current a  section  eV.,  had  mode  4.3.9  ion  due  curve of  Br"  the  The  energy  The  experimental  result  to  origin  scale  current  the  runs  that  was  much  smaller  differing  comparison  much  of  the  this  this  work,  signal  due  There  (8)  or  a  clear  is  at  approximately  pair  formation.  a  it  observed  have  been  to  broad onset  19  of  eV.  a  This  is  Bromide from  the  quadrupole  the  calibrated  in  against  SF^~  pressure  =  A.  It  was  of  the  10"  9  intensity that  be  noted  for  conditions,  for  the  It analyzer.  formation. -  3  x  at  10"  the  dissociative  observed  mm. H g ,  5  time  capture  I'/CHjI,  but  a meaningful  of peak  because  intensity  made.  potential peak  32.  multichannel  were:  x  instrument  Fig.  conditions  the  in  must  in  not  that  eV.,  scans  than  in  The  six  5  out  smaller In  I")  process.  shown  was  pointed  +  +  pair  process  peak.  instrumental  of  9  CH  ion  is  the  could  an  and  type  ion  portion in  to  halides.  CH^Br  appearance  maximum  7  is  from  of  electron  the  a  obtained  was  The  least  From M e t h y l  formation  of  methyl  formation  they  process  other  between  capture  probably  The  this  scavenging  of  Br"  at, its  observed  dissociative  most  the  that  secondary  new  in  for  (leading  is  at  of  Br"  0.2  from  eV.  CH^Br  is  The w i d t h  O.eV., of  the  and peak  136  CO  o CO CO OJ CO OJ  rf OJ OJ OJ  o  OJ  CO  —J  00 CD  Ok  >QC LU  OJ  'I  0  —  X 00  •.  i  Br  —  u  OJ  o  siiNn jLyuynayu 'iNayyra Figure  32.  The  Formation  of  Br  from  NOI  Methyl  Bromide  O  CC I— 00 C_) UJ I <° LU ^  m .  LU  137  (FWHM) a  is  0.9  eV.  maximum a t  this  latter  process  or  ion  current  and  Hamill  process  in  7.2 peak  A second eV., is  ChjBr  the is  dissociative  formation  of  the  result  five  energy  of  scale  was  experimental  conditions  observed  for  this  observed  for  I'/CH^I,  comparison at  least  ratio  of  As this  in  for  can  6  be  molecule  increase  the  processes observed  of  Melton  ion  must  pair  be  directly  above  peak.  x  the  10~  and  made.  quadrupole instrument is  the  shown  SF^"  pressure  A.  The  were  much  9  although  again  low  *  33.  be  signal  10" ion  than  weaker, no  for It  analyzer.  2 x  smaller to  responsible  Fig.  formation.  negative  appeared  The  in  multichannel  against  were:  Br'/CH^Br,  part  current  CHjCl in  species  c o u l d be  this  £rom  calibrated  *  other  the  Chloride  scans  current  those  ion  C l " from  electron  so  capture  obtained  the  than  the  C l * From M e t h y l curve  eV.,  of  of  Tsuda,  for  with  side  onset  steady  potential  the  The  the  the  appearance  to  4.3.10  for  peak  energy  A c c o r d i n g to  postulated second  The h i g h  energies.  9.6  explain  capture  i n f l u e n c e d by  responsible  higher  (157),  evident.  clearly  processes at  is  dissociative  was The  The mm. H g ,  5  signals those in  general,  numerical  intensity  was  signal  noise  for  the  poor  33,  the  structure  to  curve. seen is  from  more  Fig.  distinct  than  that  for  observed  the  halides  for  138  CO o  CC UJ UJ  O CC CJ UJ  UJ  SIINH Figure  lyuyiiayu iN3yyn3 4  33.  The  Formation  of  Cl  from  NOI  Methyl  Chloride.  139  previously peaks an  in  described.  the  first  appearance  0.2  eV.  the  width  peak. has  The  a  long  peak  is  be  made  second tail  dissociative The  the  work  dissociative this  ion.  dissociative above .  an  quoted 10.85 of  seen  in  on  curve.  The  and  peaks  narrow,  but  no  of  has  the  almost  is  seen  peaks and  4  in  Reese  the  overlap  of 1  of  the  eV.,  second and  A third  who to  hand,  some  approximately  complete  (155)  other  has  a maximum n e a r  leading  and  at  eV.  with  is  at  first  measurement  a maximum  to  peak,  Fig.  eV.  is  Cl'/CH^Cl  33  estimated  value  eV.,  kinetic  the  processes  (154),  and  of  from energy.  to the  10±1  eV.,  Dibeler  10.07  is  with  Tsuda,  photoionization value  Dibeler  agreement a  9.8  these  capture  onset  fair  of  capture  8  eV.  disagreement found  the  no  formation  found  an  additional  of  initial  structure  eV.  Also  with in  7.5  dissociative  because  peak  capture  two  O.eV.,  process  of  of  Cox  of  very  capture  are  volts  extending  observation  with  two  potential  can  This  There  the  ion  at  has pair  10.3  values Cox, and  Walker  appearance It  be  Melton  and  eV.  a prominent  of who  potential been  eV.  This  process value  and  found  a  value  (157)  with  measured  of  Cl"/CHjCl.  must  out be  is  Reese  have  pointed  process  pair  Dibeler  Hamill  (158)  ion  (154, formed  who  of a  value  the Their 158) with  that  140  4.4  Electron  4.4.1  Scavenging  Helium* The  has  been  method  threshold  studied  (86,  (88,  89).  very  good.  159) The  forbidden  momentum  clearly  when  such  the  the to  2^P  a  the  SF^  also  been  the  shown  figure  calibrated  The  * in  study, in  obtained pressure  4  x  10  it  was  yield  electron  is  =  the  of  scavenging  2  such  in  has  the  been  spin-  S as  well  as  the  2 S  show  up  very  as  these  either  electron  technique  workers  previously, the  helium  trapped  1  optically-allowed  terminated  the  instrument  pressure  by  various  as  However,  work,  this  conditions:  their  spectrum  counterparts  previous  at,  or  studies,  very  near  potential.  sense,  was  to  state.  of  spectrum  mentioned  helium such  result  was  the  forbidden states  this  from  by  among  been  of  has  relative  resulting The  but  ionization In  in  only  compared  spectrum the  not  As h a s states  impact  repeatedly,  agreement  angular  as  electron  using SF^  mm. H g ,  I s h o u l d l i k e to thank the s c a v e n g i n g s t u d i e s  of  energy  zero  impact  34.  against  excitation  to  on  The  the  the  primary following  =  x  10~  electron  peaks  are  M r . R. of the  6  measure  electrons of  helium.  scale  SF^"  of  this  peak.  This  experimental  mm. H g ,  current  clearly  to  monopole  energy  the 4  attempt  ionization  performed  Fig.  of  decided  =  seen  Eaton for his rare gases.  total 1.5 in  x  10"  the  A. energy  collaboration  141  s i i N f i Aybyiiayu 'iNBuyno Figure  34.  The  SF  6  Scavenging  Curve  of  NOI  Helium.  142  region by  an  seen  from  19  to  extremely by  other is  well  the In  for  might  serve  as  would  predict  his  an  comparisons  should  be  Temkin  (161)  (89,  159).  it  guide  rise  It  of  as  (E-IP)  (E-IP)  must  0 , 1 2 7  shown  be  in  the  pointed  the  nature  two  energy  which  is  which  should  been  sight,  at  energies  out  inherently be  comparison  done  yield  curve  has  above  threshold,  been and  threshold  this  whereas  that  of  Wannier  36  that of  these  emerge  the  the be  Firstly,  be  near  zero  increase  of  to  than  attempt  has  theory  been  made  the one  measured  that  curve  Temkin's predictions. experimentally  by  only  experimentally  the  of  scavenged  applied  threshold  the  respectively.  threshold  with  would  about must  the  of  (69)  comparisons  caution.  near  both  at  the  yield  and  35  law  has  Figures  that  with  (160)  that  n o r m a l i z e d to no  the  results  must  sharper  here,  of  potential  The  Thus,  compared  ionization  relative  increase.  electrons  emerge.  the  predicts ,  Temkin's predictions  curve  the  a  the  utmost  consequence,  of  that  marked has  first  out  emphasized  as  zero  at  pointed  0 , 5  energy,  of  is,  is  This  signal  (65)  electrons  yield  What  i o n i z a t i o n . Temkin  both  SF^.  signal.  &  the  the  theory  are  has  to  ionization,  the  SF "  of  above  single  viewed with  and  the  rise  was  scavenging a  that  should  two  2,5  impact  curve  ionization potential  rise  continuing  Sec.  electron  The  threshold.  curve  indicated  rapid  the  yield  for  eW  workers  surprising above  24  In  measured at  5.5  eV.,  to  correct  143  s11 Nn x y u y n a y u 'lNayyro NOI 0i 5  Figure  35.  Comparison Results.  of  E  with  the  Helium  Scavenging  144  s i i N n Ayuynaab Figure  36.  Comparison Scavenging  of  UN3yyra fc  0,  1  2  Results.  7  with  the  NDI Helium  145  for  the  error  Because  of  present  the  width  work,  the  problem  first  few  hundredths  possible  that  and  the  lack  ion  chamber  ion  space  a  would  the  the  of  SF "  peak  &  only a  ionization  affect  volt.  the  mechanism  for  their  result  in  the  growth  This  might  and  the  in  this  comparison  Secondly;;  production  efficiency  potential.  observed  continual  charge.  scavenging  of  should  the of  near  of  it  may  in  be  positive  removal of  the  ions  from  a weak  the  positive  have  had  some  effect  SF  ion  collection  on  the  efficiency  6 as  a  function  effect  of  electron  would not  ionization present  be  energy  present  potential,  and  and/or  when  it  is  time.  scavenging difficult  comparison,  it  describe  prediction  reasonable  is  the  is It  in  mind  the  possible  s h o u l d be  made  not  in  the  deficiencies  in  the  and  indicate  of  the  threshold  of  Wannier.  an  i n d i c a t i o n ; that  The  described  law  is  direct in  (E-IP)  results  clear a  "  increase  very  at  this  predicted  well.  point  does  The  0  experimentally  n  1.5  =  Temkin's  study 4.1.1  of  threshold approach  more the  (E-IP)  be  5  the  rise  in  measured law.  to  realistic  positive  should  that  (E-IP) •  the  somewhat  Sec.  127  satisfactory.  between  current  an  the  experimental  agreement  does  that  more  offers  helium  seen  somewhat  scavenging  curve  to  the  assess  0  the  below  an  situation. Bearing  not  Such  the  It  simply  problem  than  that  ionization  regarded  as  a  of much  146  more  satisfactory  preference  to  test  the  of  any  scavenging  derived results  threshold discussed  law, in  in  this  section.  4.4.2  Hydrogen The  the  monopole  result gas  instrument  three  pressures  total of  of  scavenging  used  pressure  Fig.  37  scans  hydrogen  ionization from  the  in  x  displayed  in  and  above  ionization  v  0->2  »  and  the  levels  Vroom  potential  of  (58). show  Lessmann The  sense  with  spectrum  a  run  160  of  of  potential  The  remaining  positions  spectrum  are  of  the  as  of  are  measured  several  hydrogen  peak.  6  features  and  The  arrows  Frost,  above  found  which  positions by  of  the  states  (162)  the  mm, H g . ,  6  SF "  energy  markings  the The  below  47.  from  scale  various  occurring  reference  H^* ion  10~  energy  Richardson  the  the  photoionization and  Fig.  eV.)  was  analyzer.  primary  are  levels  data  are  the  It  »' 7 x  H g . The  diagram  (15.4  spectroscopic  SF^  obtained  37.  multichannel  mm.  The  hydrogen  in.Fig.  against  the  spectrum.  of  pressure  10"^  on  potential  shown  the  calibrated  Indicated the  is  were:  • 4.5  was  spectrum  the  of  at the  McDowell ionization  peaks  in  the  produced  by  Comes  (163). scavenging fairly by  low  Schulz  spectrum  shown  resolution (86),  and  an  agrees  trapped  in  a  electron  excellent  high  general  II I  2 per  I  III  ^  II  3 4  3  2 2 2  «  H2  S F ~ /  V/////A  and  I Richardson  (Photoabsorption)  |  Vroom  (Photoelectronspectroscopy)  \  C o m e s a L e s s m a n n (Photoionization)  *  **** -i  6  1  1  1  8 E L E C T R O N  1  IO  1  i  1  12  E N E R G Y ( V O L T S )  1  14  i  i  16  1  1—  18  148  resolution Referring of  spectrum to  Fig.  structure  not  noted  triplet  until  states  scavenging arises  due  some  states.  gained the  2.5 to  in  it  the  be  too  37  is  a a  That  of by  ion,  or  the  in  this  ion  and  small  in  to  be  does  be  continuum  et.  any  section  of  would  autoionizing  as  al.  about  scavenging  in  above  of  Also,  happening.  not  cross  interesting  the  the  been  technique  a neutral at  eV.,  hydrogen  information  Taylor  the  conspicuous  region.  some  the  (16).  position  reproducible,  of  of  is  of  13  has  excitation  no  that  and  Sharp  scavenging the  excite  states  study  the  might  the  11  that the  indication  majority  and  a  (16).  hydrogen  to  Dowell  either  negative  this  in  the  triplet  Sharp  distinct  approximately  by  hoped  feature  a  sufficient  on  seen  and  excitation  is  hypothesis  since  An Fig.  of  structure  hypothesis,  that  Franck-Condon region  that  observe  may  data  be  of  seen  molecule.  between  was  test  distinctive  indicate to  the  levels  crossing  curve  energy  Unfortunately,  in-Sec.  Dowell  discrete  potential  could  by  anticipated  useful  structure  is  excitation  was  ionization  vibrational  no  of  it  demonstrated  It  give  to the  the  convincingly  the  37,  signal  from  obtained  could (98)  be  regarding  potential  11  eV.  curve  the  discredit  for  this  the  spectrum  energy  There  which  However,  way  discussed  would failure  Taylor's  occurrence  detectable. feature which  of  extends  to  higher  is  shown  in  energies  149  from  approximately  the  other  the  result  of  H  the  structure of  This  2 >  studies  is  available the  limit  limit  near  of. the  4.4.3  6.5  state  It  is  shows  induced  work,  examined  potential features  Fig.  phenomenon  dissociative  (22,  are  the it  origin  is  of  due t o  some  o b t a i n e d by  extending might  transitions  the  a Franck-Condon  explain  continuum  in  Although  this  the spectrum  38  the scavenging i n the energy  (12.13  eV.).  in this  to  a  lower  be a n o t h e r to  example  describe  165).  shows  the p r o x i m i t y ground the  state  sum o f  of the of the  four  scans  spectrum range  There  o f xenon  above  are  the  has  first  several  spectrum.  a detailed  2  is  to  state  +  approximately  of the Franck-Condon P r i n c i p l e  this  carefully  interesting  The  is  continuum unless  the  This  to  Z u  distinctly)  8 e V . , of energy  However,  3  Xenon  ionization  in  n o t as  of hydrogen,  difficult  of the  c o u l d be  and o f S c h u l z .  be i n a c c e s s i b l e  eV.  impact  In been  (although  approximately  also  The continuum  underlies  the d i s s o c i a t i v e  and Sharp  effect.  failure  electron  to  portion  (86)  seen  ground  (164).  instrumental  of  apparently  of the repulsive, state  the  until  initial  Schulz  is  of Dowell  thought  transition  curve.  the e x c i t a t i o n  e V . above  state  e V . , and which  i n the  feature  dissociation 4.5  6.5  scan  of  the energy  region  2  p 3  / 2  a n t i  ion is  the  1/2 2  s  t  a  t  e  °^  s  ^3/2 state.  i n the m u l t i c h a n n e l  t  n  e  i° « n  F i g . 38  analyzer.  The  150  siiNn Jiuuyiiaybf 'iN^yyno NOI Figure  38.  The  SF  &  Scavenging  Curve  of  Xenon.  151  energy SF^" mm.  scale  peak.  was c a l i b r a t e d The p r e s s u r e s  Hg., total  pressure  Indicated energies marked  of  the  on t h e  with  used  were:  = 8 x  10~  by a r r o w s  first  are  to  the  pressure  primary SF^ = 5 x  10"^  mm. H g .  5  on F i g . 38  two i o n i c  diagram  respect  states  the peak  are  the w e l l  o f xenon  energies  of  known  (166). the  Also  members  2 of  Rydberg  These of  Series  energies  Huffman,  two  were  Tanaka  contribute  diffuse  series  and  one s h a r p  the  sharp  structure and  fact  is  detects site  Series  only  with  > -  5p nd  a  5  to  t  e  o  f  t  are the  curve.  n  e  i  5p -*-5p ns * . 6  5  o  n  '  data  actually same  limit  There  by H u f f m a n  1  on F i g . 3 8 ,  is  that  the  a  locating  quite  are  with  above.  known  scattered  clear  scavenging  associated  energy.  indicate way o f  it  irrelevant,  the  zero  6  indicated  mentioned  largely  5p "  i n the  e V . , c a n be  Rydberg  converging  designated  F i g . 38,  Series  t  et.  i s one  a l . ,  Two l i n e s and are  of  identified  s.  occurring  13.5  Rydberg the  are  s  There  the p h o t o a b s o r p t i o n  series  From  ^/2  (167).  Series  designated  superscript  p  from the p h o t o a b s o r p t i o n  and L a r r a b e e  to  series  on t h e  measured  o v e r l a p p i n g Rydberg  which  by.a  converging  to  curve the  Although be  since  the  technique  states  between  excitation  of  leaves  these  o f the  (166),  in ionization  of this  technique the  results  may w e l l  the  12.5  t h e members  scavenging  which  Nevertheless,  discrete  some  autoionizing  electron  scavenging  that  collision on x e n o n  prove  t o be  continua.  152  structure  In  the  at  the p o s i t i o n  corresponding The  curve  this of  is  spectrum  to  tends  the to  obtained of  formation  smooth  of  the  surprising  that  this  scavenging  spectrum,  there  ionization  of  out  in a l l likliehood  new m e m b e r s  the  here,  the  *Pl/2  is  potential -state . of  at  the  appropriate  due t o  the  cessation  Rydberg  Series.  new i o n i z a t i o n but this  is  It  is  the i o n .  energy,  of  seems  event  no  excitation  quite  not seen  reproducibly  but  the  i n the  case.  It  2 may  be n o t e d  conspicuous but  the  results  that  connection is  xenon  were  not  shown the at  is  the  2  a  shown  n  d  Xe  + +  3  indicated diagram  as  2 p  show  the  those  absorption  data  is  not  of Nicholson and the  Marked s  t  a  t  first  e  s  o  Clearly,  t  n  formed  e  of  diagram i  o  n  (166), present  potential  on t h e  estimated  conditions  0^  5s-^np edge  from  the  Samson  energies  lines  xenon  are  on t h e series at  (168).  u n i d e n t i f i e d features  of  energy  energies  (n = 6-*-°°) of  curve  and the  These  vertical  the  are  (ioo),  (109).  The s o l i d  indicated  spectrum  f  ionization  f o r the previous  on t h e  energies  were  the  The e x p e r i m e n t a l  employed  converging  lines  P j ^ state  observation  above  i n F i g . 39.  i/2  is  energies  vertical  the  this  scan  by a r r o w s .  transitions  of  clear.  i n F i g . 38.  which  These  between  extended  same  P /2  onset  i n the p h o t o i o n i z a t i o n  An of  the  of  23.39 eV. The dashed  i n the  (168). this  series  of  autoionizing  energy  levels  X K  \  I  •<u X  r  f.  siiNn iyyyuayu .Figure  39.  The  SF  'iNByyno  Scavenging  Curve  of  NOI  Xenon.  154  is  contributing  structural unusual in  profile.  electrons  loss  from  the  range,  cross  discrete  scattering  feature  Henglein  4.4.4  (170)  of  curve  previously  were  called  been  of  this  species as  seen  feature  in  this  "window" resonances).  which  doubly  is  charged been  xenon  seen  of  the  continuum  i n F i g . 39 apparently  in  This  by t h e i n t e r a c t i o n  of note  has p r e v i o u s l y  (168)  decreases  the u n d e r l y i n g i o n i z a t i o n  the  h a s an  o f 90 e V . ,  manifested  caused  current  the  In the p h o t o i o n i z a t i o n  studies  levels  (so  final  production  This  (169).  with  the scavenging  the  is  the  increase  associated  i o n near  by J a c o b s  (171).  with  33 e V .  and  (100) .  Carbon Dioxide The  monopole  scavenging  instrument  result  of  six  pressures used total  Indicated  curve  shown  on t h e  2  obtained  i n F i g . 40.  pressure  respect  of  SF  This  = 4 x 10"  fc  mm. H g .  to  diagram  a variety  for C0  i n the m u l t i c h a n n e l  = 5 x 10"*'  with  CO- using  is  scans  were:  pressure  calibrated  of  of  apparently  The  the  study  the  although  i n the  have  xenon  levels  produce  levels  these  is  they  current,  These  section  phenomenon  scavenging  that  photoabsorption  energy  in  the  feature  an e n e r g y  and  to  the  are  the  curve  was  6  mm.  The  Hg.,  scale  was  S F " peak. 6  results  techniques.  the  analyzer.  The energy  primary  from  of previous  Below  the  studies  ionization  MHMZmr  77MMM  / / / / / / / I Price a Simpson (Photoabsorption) •V»V*Vf> Dibeler a Walker (Photoionization)  | |  r 2  4  6  8  T  IO  ELECTRON  T 12  14  E N E R G Y (VOLTS)  Tanaka et al. (Photoabsorption) Tanaka a Ogawa  T 16  18  (Photoabsorption)  20  156  potential, and  regions  Simpson  strong  absorption  Various Jursa  (172)  of  LeBlanc  indicated  by  indicated.  are  indicated  potentials (173)  arrows.  and  subionization the of  photoabsorption Inn,  Watanabe  continua The  region  greater the  with of  than  is  the  is  no  small  negative was  transmission. 3.4  eV.  The  scavenging  data  Ogawa  obtained  by  relatively  This  spectra  of  Zelikoff  hatching.  of  Tanaka,  (174) in  are  the  Dibeler  and  featureless  is  not  surprising,  Price  and  Simpson  (176)  consist  closely  optical  (at  10.8  eV,)  up  feature  of  shows  and  of  peaked  absorption  the  since  (172)  mainly  spaced  in  structure.  energies clearly  in  curve.  interesting but  distinct  Hasted  in  (178)  The  near  their  work  energy  possibility  measurements,  the  structural  absorption  resonance  manifested  the  of  cross-hatching. is  2  approximately  and  ion  by  C0  strongest  known o p t i c a l  Boness  curve  superimposed,  scavenging An  but  a  from  tier  structure  range,  and  taken  second  peaked  for  energy  a  Price  relatively  Finally,  indicated  curve  by  of  and  Walker  The  Regions  by  Tanaka  efficiency  is  found  of  photoionization (175)  absorption  are  ionization  and  optical  of of and  in  C0  subionization  feature 2  in  this  have  discovered  this  energy.  as the  a  detecting the  in  such  4  eV.  region  a  This  decrease minimum  near  in  There  (177),  temporary resonance electron  their  study  resonances  qualifications  region  which  was  via must  157  be  met  by  covered peak  the  in  near  resonance  Sec. 4  forbidden  eV.,  is  It  is  first  seen  as  a  distinct are  scavenging  curve,  there  excitation  is  Carbon  of  used mm.  but  15  and  four  scans  Hg.  The  primary  SF^"  experiments  the  of  have  course,  excitation  is  in  to  an  of  Fig. to  been  that  of  an  C0  40,  at  2  the optically  13.78  the  perceive  curve  in  eV .  Higher from  i n d i c a t i o n that the  the  discrete  energy  eV,  curve  for  in  COS o b t a i n e d  Fig.  41.  pressure  SF  =  energy  scale  peak.  The  fe  included  C0 *  ionization potential  2  Simpson  The  (indicated  of  Jursa not  and  found  x  was  . by  in  of  The  of  the  in  with  optical  (179). latter  was  =  taken  8 x to  fashion  the  10" the  impact  absorption  from  the  pressures  respect  same  spectroscopic were  the  The  photon  the  estimated  arrows)  curve  pressure  various  41  from  analyzer. total  6  Fig.  were  LeBlanc by  10" ,  The  calibrated  regions  (172)  potentials  8  results  the  potentials  in  multichannel  done  Tanaka,  is  shown  was  and  step  the  are  for  18  scavenging  instrument  were:  Price  detectable  Oxysulfide  The  sum  to  difficult  contributing  between  monopole  be  ionization potential  potentials  4.4.5  to  possible,  corresponds  ionization  region  it  state. The  (173)  2.5.  for  as  below  work  of  ionization from  the  data  Two i o n i z a t i o n workers  but  seen  in  the  5  PES  I.R  SFJ-/COS LP  PES  7  I.R  P r i c e a S i m p s o n ( Photoabsorption )  $$$8&$4  Dibeler a Walker (Photoionization )  |  T a n a k a et al. (Photoabsorption )  A l - O o b o u r y , M a y a Turner ( Photoelectron i  IO  ELECTRON  12  l<4  16  T  T  20  —I—  22  spectroscopy) T  —I  2«4  i  E N E R G Y (VOLTS) 00  159  photoelectron Turner  (180)  prominent Dibeler  spectroscopy are  ionization  in  Walker  The  optical  indicated  structure  and  a  comparison  present  the  work.  optically  Thus,  observed  discrepancy  not  this is  The  hold  of  of  the  the  11.5  for  most  of  rapid  rise  of  thanl3  eV.,  can  by  the  mechanism  with  the  inherent  basis)  to  with  make  the  contribution  rise  The  curve.  of  ionization  in  reason  the  the  species  current for  this  of  produced,  the  producing although  at  in  In  ion. two  the  this  at  least  autoionizing  into  This  by appears work.  energies partially states  addition,  excitation  COS*  marked  observation  current  u n d o u b t e d l y be of  not  studied  scavenging  c o u l d be  for  are  This  ionization potentials.  continua  ion  the  eV.  excitation  dissociation a  first  difficult  spectroscopic to  the  made.  ionization potentials  true  for  be  of  apparent.  mechanism  each  estimate  of  at  contributing  for  peak  scavenging  inner  provide  by  and  hatching.  well  the  is  peak  the  accounted and  a  in  very  greater  work  reasonably  it  can  curve  cross  of  May  Finally,  COS b e l o w  Because  correspond  not  Inner  to  no  position  does in  structure  (on  of  by  spectrum,  forbidden states The  potential  spectrum  optical  arrows.  indicated  spectrum.  of  Al-Joboury,  crossed  correlates  complexity  of  photoionization  is  scavenging  absorption  by  the  (175)  potential  detailed  curves  another  the  various  process  zero  energy  actual  energy  would  electrons distribution  160  of  the  electrons  threshold abundant ion  This  generated  i o n has  The o t h e r  i o n with  +  conceal  any s t r u c t u r e  autoionization  Carbon  result  of  five  is  f o r the previous  data  of  resolution Henglein  on t h e  much  the  of  from  most S  continua  inner  +  13.65 e V . COS i s  approximately  the  17 e V .  might  ionization  of CS  pressure  * 6 x  10"  5  well  potentials  Tanaka  The c u r v e  analyzer.  et.  obtained  was t h e  = 6 x  6  The  10"  A s was  impact (179), (180)  similar  6  energy  a l . a l .  the  The  SF^ peak.  et.  is  from  curve  the photon  and A l - J o b o u r y  spectrum  This  of SF  the primary  (182),  diagram.  obtained  mm. H g .  two m o l e c u l e s ,  (175)  2  i n F i g . 42.  were:  against  scavenging  to  by J a c o b s  are  a low and  (100). The  is  of  the  species.  spectrum  and Simpson  andWalker  indicated  is  potential  i n the multichannel  pressure  done  Dibeler  normal  shown  conditions  was c a l i b r a t e d  Price  impact  dissociation  due t o  above  In COS, the  fragment  potential  this  scans  Hg., total  scale  continuum.  by e l e c t r o n  these  scavenging  instrument  experimental mm.  of  complex  Disulfide  The monopole  of  fairly  positive  an a p p e a r a n c e  Excitation  4.4.6  be  an a p p e a r a n c e  abundant  (181).  or  likely  the d i s s o c i a t i o n  fragment  (54).  (175) . CO  of  would  more  structure prominent  seen than  below that  the  seen  ionization for C0  2  potential  and C O S . The  SFT/CS  I.p.  2  RYDBERG  WZZZL  •  Y/////////A  I.R  P r i c e a S i m p s o n ( Photoabsorption )  X////////A  Dibeler a W a l k e r  ( Photoionization )  Tanaka e t a l .  (Photoabsorption)  A l -Ooboury a Turner ( Photoelectron l  3  5  I  T  6  7  8  9  IO  ELECTRON  11  13  14-  E N E R G Y (VOLTS)  15  i 16  17  spectroscopy)  18  ~1— 19  20  162  correlation Price  and  of  be  of  curve,  were  can  be  on  the  curve  this  Walker the  15  obtained  apparent,  (175).  for  contributing  be  Clearly  to  between are  at  data  although  seen some  signal some  the  to  of  the  the  curve  scavenging  ionization potentials  that  features  the  the  work  extent  levels  other  curve. are  of  to  present  in  which  curve  identified  Again,  the  were  Dibeler  discrete  for  curves  photoionization  from  and/or  The  ratio  potential  scavenging  species.  of  noise  confidence  These  ten  the  to  ionization  real.  least  this  curve  the  with  dominate  can  photoionization  excellent  stated  on  peaks  species  inner  optical  forbidden states  eV.,  present  autoionization for  the  it  reproducibly  of  of  approximately  which  the  dismissed.  undulations and  with  readily  optically  Because this  structure  Simpson is  contribution cannot  this  and in  levels  no  are  indications  the  scavenging  work. The 15  eV.,  can  rise  of  two  abundant  16.16  eV,  the  p o s s i b l y be  continua most  of  the  (175)  ion.  The  S  +  at  correlated  fragment  for  current  and  with  appearance positive CS  +  energies  in  dissociation  potentials ions  excess  are  respectively.  of  14.81  the and  of  REFERENCES  H.  D. Smyth,  W.  Brode,  J.  B.  Rev. Mod. Phys.,  ibid.,  Hasted,  257  "Physics  Butterworths , D.  R.  Bates,  Academic R.  Press,  N . Compton, P.  K. C u r r a n ,  W.  M. Hickam  J.  L.  G. Christophorou  Oak R i d g e  National  and  Laboratory  (1966).  Phys.,  E.  Processes",  Fox,  £ 8 , 780 J.  (1963).  Chem.  Phys.,  25,  (1956) .  Jacobs  R.  N . Compton,  and A . H e n g l e i n ,  0.  Klemperer,  R.  E.  J.  Rept.  Chem.  Prog.  F o x , W. M . H i c k a m ,  Phys. some  R e v . , £ 4 , 859 representative  R.  E.  Fox, J .  D.  C.  Frost  Chem.  A232 ,  L.  a n d W.  Melton 546  P.  Phys.,  Phys., T.  (1964) .  Spec,  3_,  W. 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(London),  APPENDIX  The  The properties velocity derived  the  of  by  it  is  a  Selector  review  cylindrical The  Hughes  and  of  relations  Rojansky  as  IE =  -P/r_,  center  An e l e c t r o n  experience  towards  illustrated  the in  a  where  the  (mass  force  center the  of  of  (small  electron below  were  (101).  electrostatic  common  focussing  described  the  being  the  electrostatic  Consider  constant. would  the  selector.  cylinders from  following  127°  I  field  r_ i s  a  cylinders, m,  charge  magnitude r).  accompanying  radius and  -e) eE  the  this  tending the  coaxial vector  P is  in  Consider figure.  between  to  field  field deflect  situation  177  If at a  an e l e c t r o n  the p o i n t specific  will  A , then  value  describe  V  motion  detected  at  figure.  The requirements -eE  However,  * mv o  i n order  of  such  an  electron  an  angle  it  a(path  but with  it  experience  necessary V  a  r  «  q  is  a velocity  to  forces  Since,  f o r the  acting  then  If  the independent dr/dt  a^  »  -  consider into  =  • Pe. properties  cases  wherein  the f i e l d  is  at  injected  r)  on t h e  which  particle,  can be  resolved  and a t a n g e n t i a l  component  of the a c c e l e r a t i o n  £  are:  2  2  -  a  r  2  + <|> ' a  2  2  under  • 0.  consideration,  Therefore,  variable  is  a central  force  r*d<f>/dt = c o n s t a n t = h = r v  changed  0  from  t  t o <j>:  (dr/d$)(d^/dt) d(f./dt  dr/dt  1 i n the  d / d t (r d<|>/dt)  case  is  electron  that:  2  mv o  acting  components  2  1/r  the  be  and c o u l d be  are  a •  will  field  vK V ^ ,  d r/dt -r(d<fr/dt) 2  there  where  an e l e c t r o n  (along  These  this  focussing  injected  an a c c e l e r a t i o n  component  b y 4>.  the  into  path  orbit  , or: o*  investigate is  speed  designated  = Pe/r  o  of P,  i n the f i e l d  for this  the e l e c t r i c a l  a radial  described  r  is  2 ) , and where  of  into  /  of velocity  Because will  2  to  a field,  normally,  This  B.  normally  value  the e l e c t r o n  circular  point  injected  f o r a given of  q  is  (h/r )(dr/d*) 2  » h / r  2  0  cosa.  178  and  a variable  defined by:  dr/dt Therefore: In  - a  the f i e l d ,  -Pe/r  » -hdu/d$, 2  2  2  2  2  introduced, '- - h u  2  2  then:  d u/d4> .  2  2  2  • u).  2  will  experience  a force  g i v e n by  cos o/mv*  • Peu/m.  of the v a r i a b l e  allows  2  equation  y=u/u =r /r o  Following  the d i f f e r e n t i a l  + y • c  2  is  at  this  + u)  2  and t h e  Q  2  Hughes  with  y » l ( i . e . r=r ) and R o j a n s k y , equation  the i n i t i a l and d y / d $  Q  differential  to be  (101) are,  conditions:  «  -tana.  approximate  f o r angles  solutions  +a a n d - a :  y j • c • ( l - c ) c o s / T 4> - ( t a n a s i n / 2  $)  /72  -at  y  $)  //?.  = c +  2  For an a n g l e  where  y^  Therefore: Therefore $=n//2  y  2  .  This  (/2<J>)  0  The separation  l  second  II,  o f two e l e c t r o n s ,  differing  when  energies.  one  this  of  o f t h e two c r o s s  the term  (tanasin/J  entering refocus, will <f>)  be  vanish  radians.  f o r the f i r s t  that  factor  velocity,  - a , the p o s i t i o n  2n, e t c .  cross  Note  at  the o r b i t s  occurs  » 0,  the o r b i t s  = 127 17 .  slightly  where  $ +(tanasin/2  of equal  +a a n d t h e o t h e r  the p o s i t i o n s  (l-c)cos/2  two e l e c t r o n s  i.e.,  written:  /y.  t o be s o l v e d  4>*0,  equation  •a  at  quantity  2  d y/d*  to  2  h u (d u/d<fr  2  This  2  the p a r t i c l e  introduction  c*Pe  d r/dt  = h u (d u/d<fr  r  is  =-Peu.  Therefore: The  u«l/r  angle  time is  at  independent  t o be i n v e s t i g a t e d entering Consider  normally, one such  is  the  of a. spatial  but with electron  as  179  having a  the  appropriate  different  orbits  will  minimum.  speed be  speed  g i v e n by  greatest  y=c+(l-c)  Therefore: This the  cylindrical  to  electrostatic  q  and The  when y  is for  has  the  second  separation either a  sin(/2>)  <|>»II//2  treatment  optimum p o s i t i o n  v.  cos(/2  dy/d<j>*-/2(l-c)  V  «=  as of  having their  a maximum o r  a  0.  =0.  «= 1 2 7 ° 17 » . shown t h a t  intercept  the  analyzer.  the  angle  electron  127°17'  beam  in  a  is  APPENDIX  Un ionization is the in  listed  page  181,  efficiency  of  counts  the multichannel  break  of  curve  analyzer.  be  i n channel  in  an a b s o l u t e  67.  by c o n s i d e r i n g  from  of  of  0.0426  scale  4.2.1.  350 scale  that V.  the b a s e l i n e  The v o l t a g e  sense.  i n each  positive  represent  The v o l t a g e  interval  away  in Sec.  The numbers  accumulated  a voltage the  f o r the helium  discussed  form.  c a n be e s t a b l i s h e d  represents  data  curve  i n numerical  number  curve  the  II  each The  channels f o r the channel initial  was a s s i g n e d  was n o t  calibrated  to  HELIUM 4516. 4511. 4509. 4500. 4505. 4496. 4514. 4570.  5773.  7719. 9932. 12149. 14783. 17496. 20159. 22879. 25655. 28801. 31378. 34499. 37499. 40693.  43453.  46609. 49534. 52477. 55398. 58866. 61446. 64684. 67572. 70546. 73250. 76101. 79089.  4519. 4500. 4494. 4503. 4512. 4508. 4513. 4618. 5942. 791.3.10128. 12526. 14977. 17771. 20394. 23219. 25899. 28811. 31862. 34937.  4515. 4500. 4506 . 4517.. 4511. 4505. 4495. 4672. 6129. .8121. 10378. 12783. 15227. 17913. 2U831. 23436. 2b323. 29272. 32264. 35131. 38028. 41262.. 44223. 47017. 50330. 53304. 56030. 59211. 62140. 65243. 68070. 70995. 74123. 76733.  POSITIVE  4519. 4514. 4514. -4.5-00... 4498. 4496. 4512. -  4733.  IONS.  350  4514. 4509. 4500.  4513. 4509. 4504. -4505.  4495.  4499.  4504. 4514. 4846. 6511.  4504. 4512.  .4497.  49 5 4 .  6331. 6742. 8 3 2 3 . - — a 6 3 5 . - -8-7 2-1* 10617. 10832. 11042. 12933. 13220. 13444. 15549. 15756. 16053. 18177. 18454. 18736. 20967. 21231. 21436. 2 3 . 7 8 6 . .23933 . .2.4191. 26450. 26843. 27156. 29448. 29743. 30064. 32658. 32694. 33032. 35453. 35703. 35901. 3 8508. 38630. 38923. 37733. . 4 1538. .41608. 41962. 40732 . 44362. 44884. 45207. 43730. 47642. 47834. 48209. 46695. 50631. 50778. 50968. 49983. 53320. 53946. 53936. 52904. 55829. 56356. 56891. 56942. 5 9 448. 59665. 59789. 58963. 62346. 62564. 62891. 61/13. 65571. 65786. 66001. 64840. 68389. 68480. 69075. 67827. 7 1 2 9 2 . 7 1 4 6 5 . 71581 . 70654. 74316. 74516. 74910. 73659. 77023. 77451. 77572. 76532. 79 591 . 7 9 9 1 1 . 8 0 2 7 1 . 8 0 0 2 8 . 8 0 6 6 1 .  CHANNELS.  4523. 4510. 4502. 4511. 4509. 4511. - 4504. - 4505. 4502. 4503. 4506. 4498. 4523. 4524. 5087. 5254. 6920. 7157. . 9020.. 9258. 11194. 11507. 13780. 14032. 16386. 16504. 18992. 19299. 21714. 22003. -24424. 24841. 27527. 27648. 30392. 30472. 33323. 33658. 36443. 36697. 39430. 39609. 42422. 42562. 45382. 45466. 48448. 48671. 51298. 51574. • 54396. 54895. 57214. 57653. 60375. 60821. 63344. 63719. 66006. 66266. 69103. 69533. 72097. 72526. 75063. 75394. 78094. 78316. 80789. 81044.  4510. 4509. 4505. 4514. 4501 . 4512.  4502. 4505. 4504. 4502. 4506. 4509. 4537. 4550. 5457. 5621. 7324. 7542. 9431. 9454. 11739. 11940. 14286. 14535. 16831. 17234. 19581. 19859. 22261. 22639. 2 5 2 2 8 . 254.93. 28030. 28256. 31110. 31391. 34082. 34129. 36979. 37278. 39864. 40293. 42671. 43054. 45909. 46373. 49022. 49067. 5 2 u l 2 . 52257. 55u95. 55156. 580U7. 58216. 61168. 61346. 63967. 64087. 66629. 67094. 69815. 70256. 72557. 73043. 75641. 76U89. 78482. 78774. 81246. 81480.  


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