On the electron impact spectra of CH4 and CF4

Abstract

The electron impact spectra of CH4 and CF4 have been observed for electrons having incident energies of 400 and 500 eV and at scattering angles from 0° to 5°. The oscillator strength of the CH4 spectrum in the region from 8.55 to 10.95 eV was determined to be 0.28±0.04. For the CF4 spectrum, the oscillator strength was measured as 0.024±0.003 in the region from 11.95 to 13.03 eV and 0.36±0.03 in the region from 13.03 to 14.90 eV. The major features of the spectra of these two compounds are assigned as transitions from molecular orbitals of the ground state to Rydberg orbitals of the molecule. This assignment implies that the first allowed transition in the spectrum of CH4 is split due to the Jahn‐Teller distortion of the excited state. The dependence of the differential cross section for electron scattering upon scattering angle for such Jahn‐Teller transitions is analyzed and compared with the observed relative intensities in the spectra.