Structures, energetics, and reactions of [C2H3S] radicals and [C2H3S]+ ions : A Gaussian-2 ab initio study

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Original languageEnglish
Pages (from-to)3028-3037
Journal / PublicationJournal of Physical Chemistry A
Volume104
Issue number13
Publication statusPublished - 6 Apr 2000
Externally publishedYes

Abstract

A detailed computational study on the structures, energetics, and reactions of the isomers of the [C2H3S] radical and the [C2H3S]+ cation has been carried out. The computational models used are slightly modified versions of the ab initio Gaussian-2 method. Ten [C2H3S] isomers have been identified. Among them, the thioformylmethyl radical (1) has the lowest energy, with a Delta;Hf0 value of 214 kJ mol-1. Other more chemically important isomers include the thioacetyl radical (2), thiiranyl radical (4), 1-thiovinyl radical (8), and 2-thiovinyl radical (11, 12, 13, 14); the Delta;Hf0 values for these isomers are 251, 301, 314, and 342-347 kJ mol-1, respectively. In addition, we have also studied various reactions involving these radicals. For instance, it is found that isomerization reactions of 1 to 2, 4, 8, and 12 have barriers ranging from 123 to 227 kJ mol-1. On the other hand, reaction 2 → 3 proceeds via a dissociation/recombination mechanism: 2 → CS + CH3 → 3. The dissociation process is the rate-determining step, with a barrier of 187 kJ mol-1. On the [C2H3S]+ potential energy surface; 12 isomers have been found. Among them, 2+ has the lowest energy, with a Delta;Hf0 value of 891 kJ mol-1. Other isomers with Delta;Hf0values within 200 kJ mol-1 of that of 2+ include 8+, 4+, 5+, 1,+ (triplet state of 1+), and S-protonated ethynylthiol (16+). Reactions involving these cations studied in this work include: 4+ → 2+ (barrier being 116 kJ mol-1) and 4+ → 8+ (152 kJ mol-1), both having 1+ as the transition structure; 1,2-H shift reaction 4+ → 5+ (219 kJ mol-1); 1,3-H shift reaction 8+ → 16+ (232 kJ mol-1); 8+ → 2+/4+ (162 kJ mol-1); and 8+ → 5+ (171-175 kJ mol-1) with two distinct pathways. The Delta;Hf0 values for various species calculated in this work are in good accord with available experimental measurements. Furthermore, the kinetics data reported here for reactions involving [C2H3S]+ cations are consistent with the results obtained in low-energy collision activated dissociation experiments. © 2000 American Chemical Society.