Dissociative photoionization of CH_3SSCH_3 in the region of approx 8 - 25 eV

摘要

The dissociative photoionization of CH_3SSCH_3 has been investigated in the photon energy range of approx 8 - 25 eV with a molecular beam/photoionization mass spectrometry/threshold photoelectron spectrometry system using synchrotron radiation as an ionization source. For dissociation above photon energy of 11.5 eV, six fragment ions of CH_3~+, C_2H_3~+, SH_3~+, HCS~+, S_2~+, and CH_2S_2~+ were reported for the first time. The photoionization efficiency spectra for the parent ion and for 12 observed fragment ions, CH_3~+, C_2H_3~+, SH_3~+, HCS~+, CH_2S~+, CH_2SH~+, CH_3SH~+, CH_3SH_2~+, CH_3SCH_2~+, S_2~+, CH_2S_2~+, and CH_2S_2H~+, were measured; their branching ratios as a function of photon energy were derived. Ionization energy of 8.20 +- 0.04 eV for CH_3SSCH_3 and the appearance energy for each fragment ion were determined from the onsets of the photoionization efficiency spectra. Based on the appearance energy and existing thermochemical data, plausible structures of the fragment ions and their neutral counterparts are proposed. Fragmentation mechanisms that involve H migration and structural rearrangement in the dissociative photoionization processes are discussed.