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UBC Theses and Dissertations

Molecular spectroscopy of ionic and neutral species in the gas phase Cramb, David Thomas


This thesis details the analyses of high resolution visible, infrared, and microwave spectra of gas phase ionic and neutral molecules. The visible and infrared spectra of several ions were measured using velocity modulation spectrometers developed in the present work. In each case the ions were generated in an electric discharge plasma. The microwave spectrum of vinyl iodide, CH₂=CHI, has been extensively measured and analysed. Visible Spectroscopy using Velocity Modulation: The (6,1) and (13,6) vibrational bands of the A²IIu — X²Σg⁺ electronic transition of N₂⁺ have been recorded in absorption at Doppler limited resolution. The rotational fine structure was fitted by least squares to standard expressions. The rotational and translational temperatures have been measured and indicate an equilibrium between translational and rotational motion in the He/N₂ plasma. Infrared Spectroscopy using Velocity Modulation: The infrared spectra of HCO⁺, H₃⁺ , HeD⁺, and N₂⁺ have been observed. Two previously unmeasured lines of the v₃ band of HCO⁺ and several previously measured lines of the v₂ band of H₃⁺ were used to adjust the spectrometer for maximum sensitivity. A new line in the rotational fine structure of the v = 1 ← 0 band of HeD⁺ was analysed using standard expressions. The rotational fine structure of the (2,5) vibrational band of the A²IIu — X²Σg⁺ electronic transition of N₂⁺ has been recorded and analysed in the region 2125 - 2205 cm⁻¹. Using the vibrational origin, T₂,₅ , obtained from this analysis combined with the origins, T₆,₁ and T₁₃,₆, obtained from the analyses of the visible spectra of N₂⁺ , it was possible to determine third order equilibrium vibrational coefficients for both the X²Σg⁺ and A²IIu states. Microwave Spectroscopy: The microwave spectrum of vinyl iodide, in its ground and first excited vibrational states, has been measured in the frequency range 20 - 108 GHz. The spectrum contains strong a-type transitions and very weak b-type transitions; all contain ¹²⁷I quadrupole hyperfine structure, with several large perturbations. A procedure specially devised for analysis of such spectra, which takes advantage of the perturbations, was applied to produce accurate values of constants that are otherwise unobtainable, and have permitted assignment of some b-type transitions. Also, as a result of this procedure, it was possible to measure both components of the dipole moment with relative ease. The centrifugal distortion constants and inertial defects have been compared with those calculated from a published harmonic force field, modified for the out-of-plane vibrations. A partial structure has been obtained.

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