Reactions of Sulfur- and Oxygen-Containing Anions with Hydrogen Atoms: A Comparative Study.

ABSTRACT

Reactions of hydrogen atoms with small sulfur-containing anions, SCN-, CH3COS-, C6H5COS-, -SCH2COOH, C6H5S-, 2-HOOCC6H4S-, and related oxygen-containing anions, OCN-, CH3COO-, C6H5COO-, HOCH2COO-, C6H5O-, 2-HOOCC6H4O-, have been studied both experimentally and computationally. The experimental results show that associative electron detachment (AED) is the only channel for the reactions. The rate constants for reactions between sulfur-containing anions and H atoms are generally higher than for the related oxygen-containing anions with the exception of the reaction of SCN-. The generally higher reactivity of the sulfur anions contrasts with previous results where AED reactivity was found to correlate with reaction exothermicity. Density functional theory calculations indicate that the reaction enthalpies, the characteristics of the reaction potential energy surfaces, and other structural and electronic factors can influence the reaction rate constants. This study indicates that organic sulfur anions can be more reactive than related oxygen anions in the interstellar medium where hydrogen atoms are abundant.