Effects of isomer coexistence and solvent-induced core switching in the photodissociation of bare and solvated (CS2)2- anions.

The photodissociation of the (CS2)2- dimer anion, known to exist in the form of several electronic and structural isomers, has been investigated at 532, 355, and 266 nm. The observed anionic fragments are CS2- and C2S2- at 532 nm, and C2S2-, CS2-, CS3-, S2-, and S- at 355 and 266 nm. In addition to the photon energy, the fractional yields of the photofragments depend on the ion source conditions and solvation of the dimer anion. Specifically, the (C2S2-+S2-)/CS2- product ratio is significantly higher when (CS2)2- is formed in the presence of water in the precursor gas mixture, even though the parent anion itself does not include H2O. On the other hand, an abrupt decrease in the above product ratio is observed upon the addition of solvent molecules (CS2 or H2O) to the (CS2)2- anion. Since the variation of this product ratio exhibits positive correlation with the relative intensity of the photoelectron band assigned to the C2v (2B1) covalent structure of C2S4- by Habteyes et al. [J. Phys. Chem. A 112, 10134 (2008)], this structure is suggested as the primary origin of the C2S2- and S2- photoproducts. The switching of the fragmentation yield from C2S2- and S2- to other products upon solvation is ascribed to the diminished presence of the C2v (2B1) dimer-anion structure relative to the CS2- based clusters. This population shift is attributed to the more effective solvation of the latter. The CS2- based clusters are suggested as the origin of the S- photoproduct, while CS3- is formed through the secondary S-+CS2 intracluster association reaction. [ABSTRACT FROM AUTHOR]