Observation and characterization of the CH ₃S(O)CH ^- and CH ₃S(O)CH ^-· H ₂O carbene anions by photoelectron imaging and photofragment spectroscopy

We report the observation of the CH ₃S(O)CH ^- and CH ₃S(O)CH ^-·H ₂O 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 ₂S(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 ₃S(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 ^- · H ₂O fragment is observed. Intriguingly, both the SO ^-·H ₂O and SO ^- products are produced with much higher yields in the fragmentation of CH ₃S(O)CH ^- · H ₂O, compared to the SO ^- yield from the dissociation of the bare CH ₃S(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.