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Inner shell and valence shell electron excitation of gaseous molecules studied by electron energy loss spectroscopy Sodhi, Rana N. S.


Electron energy loss spectroscopy has been used to obtain the inner shell electron excitation spectra of several different series of gaseous molecules. The spectra were all recorded under small momentum transfer conditions (usually 2.5 keV impact energy and small angle (~1°) scattering) and all spectral regions (both central atom and ligand) accessible by the present instrumentation (<1000 eV) have been measured. The series of molecules investigated include nitrogen containing molecules (NF₃, NH₃ and the methyl amines) and several phosphorus compounds (PX₃, X = H, F, Cl and CH₃; PF₅, OPF₃ and OPCL₃). In addition the spectra of Si(CH₃)₄ have been obtained and compared with published spectra of related Si containing compounds. All of the inner shell spectra show continuum structures which in many cases can be reasonably assigned to σ* shape-resonances. However, comparison of the inner shell electron excitation spectra of NF₃ with the X-ray photoelectron spectra (also reported here) show that continuum structure can also be ascribed, in some cases, to onsets of "shake-up" continua. The relationship of shape-resonance position and bond length is also examined in the systems studied here. The valence shell electron energy loss spectra of many of the above molecules are also reported. The assignment of these spectra is shown to be greatly facilitated by a comparison with the inner shell spectra. Finally, the inner shell and valence shell electron energy loss spectra of trans-1,3-butadiene and allene are also reported and assigned. In particular, the spectral assignment of the inner shell spectrum of allene allows clarification of its complex and controversial valence shell spectrum.

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