Low Energy, High Resolution, Variable Angle, Electron Impact Spectroscopy

Author: Rice, James Kinsey

Year: 1969

Degree: Dissertation (Ph.D.)

Advisor: Kuppermann, Aron

Committee Member: Unknown, Unknown

Option: Chemistry

DOI: 10.7907/36HJ-RS93

Abstract

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.

A low-energy, variable angle, high-resolution, electron-impact spectrometer has been designed, constructed, and put into operation. Its performance is discussed and is found to compare favorably with that of similar instruments [...].

The differential scattering cross sections (DCS) for the electron-impact excitation of helium and five molecules [(N2, CO, H2, C2H2, and C2H4)] have been measured as a function of incident electron kinetic energy (from about 20 to 60 eV) and scattering angle (from about -30[degrees] to +80[degrees]) with a resolution of 0.04 to 0.15 eV. These studies included the observation of twenty-nine electronically excited states, including 12 singlet [...] triplet transitions.

Comparisons of these results with presently available theoretical predictions have indicated the inadequacy of the latter. In addition, a theoretical calculation of the exchange excitation of ethylene [...] by electron-impact is carried out via the Ochkur-Rudge, approximation [...] and is compared with experiment.

The vibrational structure within several electronic bands has been resolved, and the relative vibrational intensities have been compared with optical and calculated relative Franck-Condon factors. Discrepancies, due to underlying forbidden transitions, have been noted in [H2], acetylene, and ethylene.

Some general "spectroscopic rules" for the identification of spin-forbidden excitations observed by electron-impact are presented. These rules are derived from an examination of the angular dependencies of the differential cross sections for twenty-six known transitions. On this basis, one state in [N2 (...)] has been unequivocally identified as a triplet, and two previously unknown low-lying triplet states in [C2H2] at 5.2 eV and 6.1 eV have been detected and characterized.

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