Selected Ion Flow Tube Studies of S+(4S) Reactions with Small Oxygenated and Sulfurated Organic Molecules

Abstract

The reactions of ground-state S+(4S) with CH3OH, CH3SH, C2H5OH, C2H5SH, CH3OCH3, CH3SCH3, CH2O, CH3CHO, C2H5CHO, CH3C(O)CH3, C2H5C(O)CH3, HCO2H, CH3CO2H, C2H5CO2H, HCO2CH3, HCO2C2H5, CH3CO2CH3, CH3CO2C2H5, C2H5CO2CH3, and C2H5CO2C2H5 have been studied with a selected ion flow tube (SIFT) at 296 ± 4 K. All of these reactions proceed rapidly, with binary rate coefficients ≥2/3kth(2), where kth(2) is the theoretical binary collisional rate coefficient. A strong correlation between the exothermicity of charge (i.e., electron) transfer and the prominence of the charge-transfer channel is observed. Extensive branching into numerous product channels occurs in many of these reactions, with channels such as charge transfer, hydride (H-) abstraction, hydroxide (OH-) abstraction, and insertion being common, although several other modes of reaction are observed. The overall reactivity of S+(4S) is similar in many respects to that of SO+(2Πr), a closely related ion that is abundant in interstellar molecular clouds (ISC). The rate coefficients and product distributions for the reactions of S+(4S) with the 20 molecules listed above are presented and discussed in terms of reaction mechanisms and product formation. Reactions of S+(4S) and the corresponding reactions of SO+(2Πr) are compared, where possible, and discussed in terms of reaction mechanisms and significance to the chemistry of sulfur in ISC.