Fragmentation of valence electronic states of SF+6studied with synchrotron radiation

Fragmentation of the seven valence electronic states of SF+6 has been studied in the range 440–810 Å by photoionisation mass spectrometry. The ion yield for SF+5 shows two thresholds at the adiabatic ionisation energy of the ground (X 2T1g) and first two excited states (Ã2T1u and B 2T2u) of SF+6. SF+4 shows a threshold at the third state (C 2Eg) of SF+6, SF+3 shows two thresholds at the fourth and fith states (D 2T2g and E 2T1u), and SF+2 turns on at the sixth state (F 2A1g). Thus in all cases the appearance energy of a fragment ion occurs at the adiabatic ionisation potential of an electronic state of SF+6, and not at the lower-lying thermochemical energy of the fragment ion. Kinetic energy releases have been measured in SF+5, SF+4 and SF+3 at photon energies just above threshold for production of each ion. In the case of SF+5 a substantial fraction of the available energy is converted into translational energy of the fragments. The relative photoionisation yields of SF+5, SF+4 and SF+3 are compared with values expected from the photoelectron branching ratios of electronic states of SF+6. The latter results overestimate the yields of SF+3 and SF+4 relative to SF+5, and possible explanations are discussed.