Electronic Energies and Electronic Structures of the Fluoromethanes

Abstract

The high‐resolution He i and He ii photoelectron spectra of all fluoromethanes in the series CH₄ to CF₄ and their deuterated analogs have been recorded and are compared with the Koopmans' theorem results of near‐Hartree–Fock calculations performed in a Gaussian basis. The agreement is very good in general and offers an unambiguous assignment of almost all of the bands observed. In particular, repeated correlations are demonstrated between the compositions of the orbitals from which the electrons are ejected and the characters of the resulting photoelectron bands. Identifiable trends throughout the series are stressed and an anomalous feature in the CF₄ spectrum is noted. Jahn–Teller effects in CH₄ and CH₃F are clearly evident, but as expected, they are not observed in CHF₃ and CF₄. Comparison of the photoelectron spectra excited with He i and He ii radiation shows wide variations in the relative intensities of various bands in certain of the more symmetric molecules, suggesting that relative intensities can be a poor measure of relative orbital degeneracies. Mass‐spectrometric appearance‐potential data are briefly discussed in the light of the photoelectron results. The carbon and fluorine $\text{1s}$ binding energies as measured with 1254‐eV x rays are shown to be electronically adiabatic. The accurate determination of the lower ionization potentials of these molecules leads readily to the assignment of several of their electronic transitions as lower members of $\mathrm{ns}$ and $\mathrm{np}$ Rydberg series.