Vacuum-UV and electron dissociative ionisation studies of SF5Cl

A complementary study of the interaction of SF5Cl in the gas phase with vacuum-UV photons and low-energy electrons from the onset of ionisation, ca. 12 eV, up to 20 eV is presented. The photon-induced experiments have used tunable vacuum-UV radiation from a synchrotron and threshold photoelectron photoion coincidence spectroscopy for product ion detection, the electron-induced experiments a trochoidal electron monochromator and a quadrupole mass spectrometer. The strengths and limitations of both experiments are contrasted, the main difference being the absence of state selectivity in the electron-induced study. The parent cation is not observed in either study, suggesting that its ground electronic state is repulsive following Franck–Condon vertical excitation. The fragment cations SF5+, SF4Cl+, SF4+ and SF3+ have been observed in both studies, with reasonable agreement in their threshold appearance energies. Using a variant of threshold photoelectron photoion coincidence spectroscopy applicable when the ground state of the parent cation is repulsive, the first dissociative ionisation energy of SF5Cl is determined to be 12.3 ± 0.2 eV, leading to a value for the adiabatic ionisation energy for the SF5 radical of 9.92 ± 0.28 eV. The electron-induced experiment is sensitive to ion-pair production, and onsets for F+ and Cl+ production have been observed which are only possible energetically if the accompanying fragments are the anions SF4Cl− and SF5−, respectively. A lower limit for the electron affinity of the SF4Cl radical of 4.88 eV is determined, a value confirmed by ab initio calculations. The electron-induced experiment is very sensitive to gas impurities, and the effects of minute quantities of SF4, FCl, Cl2 and possibly SF2 in the gas sample are observed.