Bimolecular reactions of S2+ with Ar, H2 and N2: reactivity and dynamics.

ABSTRACT

The reactivity, energetics and dynamics of bimolecular reactions between S2+ and three neutral species (Ar, H2 and N2) have been studied using a position-sensitive coincidence methodology at centre-of-mass collision energies below 6 eV. This is the first study of bimolecular reactions involving S2+, a species detected in planetary ionospheres, the interstellar medium, and in anthropogenic manufacturing processes. The reactant dication beam employed consists predominantly of S2+ in the ground 3P state, but some excited states are also present. Most of the observed reactions involve the ground state of S2+, but the dissociative electron transfer reactions appear to exclusively involve excited states of this atomic dication. We observe exclusively single electron-transfer between S2+ and Ar, a process which exhibits strong forward scatting typical of the Landau-Zener style dynamics observed for other dicationic electron transfer reactions. Following collisions between S2+ + H2, non-dissociative and dissociative single electron-transfer reactions were detected. The dynamics here show evidence for the formation of a long-lived collision complex, [SH2]2+, in the dissociative single electron-transfer channel. The formation of SH+ was not observed. In contrast, the collisions of S2+ + N2 result in the formation of SN+ + N+ in addition to the products of single electron-transfer reactions.