Gas-phase oxidation and sulphidation of Si+(2P), SiO+ and SiS+

Abstract

Experimental results are presented for a selected-ion flow tube (SIFT) study of the kinetics of oxidation and sulphidation of Si⁺(²P), SiO⁺ and SiS⁺ with the molecules O₂, NO, CO₂, NO₂, N₂O, COS, CS₂ and SO₂ at 294 ± 2K. Both adduct ions and bimolecular products were identified. The bimolecular oxidation and sulphidation reactions of Si⁺(²P) which were observed to form SiO⁺, SiO, SiS⁺ or SiS by atom or atomic anion transfer are shown to be thermodynamically controlled. Adduct formation is viewed in terms of a model involving O-atom transfer within the intermediate complex. The same model also provides reasonable mechanisms for the bimolecular oxidation and sulphidation reactions of Si⁺, SiO⁺ and SiS⁺ which were observed. The implications of the results are discussed for the oxidation and sulphidation of silicon ions in general, and in the interstellar medium in particular.