FRAGMENTATION OF VALENCE ELECTRONIC STATES OF SF6(+) STUDIED WITH SYNCHROTRON RADIATION

Fragmentation of the seven valence electronic states of SF6+ has been studied in the range 440-810 angstrom by photoionisation mass spectrometry. The ion yield for SF5+ shows two thresholds at the adiabatic ionisation energy of the ground (X approximately 2T1g) and first two excited states (A approximately 2T1u and B approximately 2T2u) of SF6+. SF4+ shows a threshold at the third state (C approximately 2E(g)) of SF6+, SF3+ shows two thresholds at the fourth and fifth states (D approximately 2T2g and E approximately 2T1u), and SF2+ turns on at the sixth state (F approximately 2A1g). Thus in all cases the appearance energy of a fragment ion occurs at the adiabatic ionisation potential of an electronic state of SF6+, and not at the lower-lying thermochemical energy of the fragment ion. Kinetic energy releases have been measured in SF5+, SF4+ and SF3+ at photon energies just above threshold for production of each ion. In the case of SF5+ a substantial fraction of the available energy is converted into translational energy of the fragments. The relative photoionisation yields of SF5+, SF4+ and SF3+ are compared with values expected from the photoelectron branching ratios of electronic states of SF6+. The latter results overestimate the yields of SF3+ and SF4+ relative to SF5+, and possible explanations are discussed.