Observation and Characterization of the CH3S(O)CH− and CH3S(O)CH−·H2O Carbene Anions by Photoelectron Imaging and Photofragment Spectroscopy

Abstract

We report the observation of the CH(3)S(O)CH(-) and CH(3)S(O)CH(-) x H(2)O carbene anions formed upon overall H(2)(+) abstraction from dimethyl sulfoxide by O(-). Photoelectron spectroscopy reveals singlet and triplet carbenes for the remaining neutral, with the singlet state assigned as the ground state. Although some formation of the distonic CH(2)S(O)CH(2)(-) radical anion is also expected, no conclusive evidence of the presence of this isomer is found. The photoelectron spectrum of HCSO(-) is also reported for the first time. Photofragmentation of CH(3)S(O)CH(-) with 532 nm light reveals two main types of anionic products: a dominant HCSO(-) fragment, resulting from methyl elimination, and a less intense SO(-) product. For the monohydrated anion, an additional SO(-) x H(2)O fragment is observed. Intriguingly, both the SO(-) x H(2)O and SO(-) products are produced with much higher yields in the fragmentation of CH(3)S(O)CH(-) x H(2)O, compared to the SO(-) yield from the dissociation of the bare CH(3)S(O)CH(-) anion. Two possible pathways are proposed as likely mechanisms for the SO(-)-based photoproducts, both involving a photoinduced intramolecular rearrangement and the formation of a C-C bond.