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

Abstract

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.

Threshold photoelectron–photoion coincidence spectroscopy study of CHCl2F+, CHClF+2 and CH2ClF+: Steric influence of the chlorine, fluorine and hydrogen atoms

“…9 These VIE values are in excellent agreement with He (I) and (II) photoelectron spectra 8,9 and, to a lesser extent, calculations of molecular orbital binding energies using ab initio methods. 10 The first four bands correspond to ionization from chlorine 3pπ lone pair orbitals, with the fifth band (ionization to ) corresponding to removal of a C-Cl σ-bonding electron.…”

“…34 The observed spacing of 1290 cm -1 is in excellent agreement with ab initio and non-threshold photoelectron studies. 8,34 Peaks are also observed at 8,10 The ground and first excited states are assigned as chlorine 3pπ nonbonding orbitals, which possess 87 and 95% Cl 3p character, respectively. 10 The B % state is a C-Cl σ-bonding orbital, whilst the next two states are both C-H σ-bonding in nature.…”

“…These values are in good agreement with those obtained from ab initio studies 10,11 and in excellent agreement with non-threshold photoelectron studies. 8,9 The ground and first excited states are assigned as the chlorine 3pπ lone pair orbitals, which possess 94 and 95% Cl 3p character, respectively. 10 The…”

“…The / E F % % states represent a fluorine nonbonding orbital and one localised on the F atom, respectively. 8 No previous assignments for the state could be found in the literature. As it is observed at a similar energy and has a comparable profile to that of the G % 2 ' I A % state of CHCl 2 F + , we provisionally assign it to have a degree of carbon 2s orbital character.…”

“…7 By contrast, there is currently a dearth of experimental data on CH 2 ClF. All three molecules have been investigated using non-threshold He (I) and (II) photoelectron spectroscopy 8,9 and by recent ab initio molecular orbital calculations. 10,11 In this study we present an extension to previous work on these three HCFCs by recording the threshold photoelectron spectrum (TPES) and threshold photoelectron-photoion coincidence spectrum (TPEPICO) for each molecule, using synchrotron radiation as the tunable VUV photon source.…”