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

Abstract

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 ²T_1g) and first two excited states (òT_1u and B ²T_2u) of SF⁺₆. SF⁺₄ shows a threshold at the third state (C ²E_g) of SF⁺₆, SF⁺₃ shows two thresholds at the fourth and fith states (D ²T_2g and E ²T_1u), and SF⁺₂ turns on at the sixth state (F ²A_1g). 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.