Vacuum ultraviolet and photoelectron spectra of fluoro-chloro derivatives of methane

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.