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The photoelectron and vacuum ultraviolet absorption spectra (200–120 nm) of CF3Cl, CF3Br, CF2HCl, CFH2Cl, CFHCl2, CF2Cl2, and CFCl3 are reported and discussed. The lowest ionization potentials belong to the chlorine or bromine lone pair orbitals, the next highest ones to the bonding orbitals of mainly C–Cl or C–Br character. In the absorption spectra the lowest freuqency bands are due to weak valence-shell type transitions. At higher freuqencies we find much stronger Rydberg type bands related to the first ionization potential. All absorption bands up to 84 000 cm−1 depart from chlorine or bromine lone pair orbitals. Some of the bands exhibit vibrational fine structure. An increase in the number of the fluorine atoms causes a shift to either higher or lower energies of the ionization potentials belonging to orbitals of mainly C–H or C–Cl character according to the cases while the lone pair ionization potentials and the absorption spectra shift to higher energies in all cases.

The vacuum ultraviolet spectra of the complete series of fluoroethylenes were measured from 2000 to 1150 Å under moderate resolution. The π*←π transitions are easily identified in all the spectra. In most cases their maxima are only slightly displaced from their position in ethylene, but a very large hypsochromic shift is found in going from the tri- to the tetrasubstituted derivative. Three Rydberg series are observed in all the spectra, converging to the π ionization potential. They all exhibit vibrational fine structure dominated by C=C stretching and twisting vibrations. In the highly fluorine substituted ethylenes the first Rydberg band is well separated from the π*←π band (at about 1900 Å) as in the highly alkyl substituted derivatives. There is no evidence for transitions of σ electrons in this part of the spectrum except perhaps at the high frequency end of the range (1200 Å).

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