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

The photodissociation of the (CS(2))(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 CS(2)(-) and C(2)S(2)(-) at 532 nm, and C(2)S(2)(-), CS(2)(-), CS(3)(-), S(2)(-), 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 (C(2)S(2)(-) + S(2)(-))/CS(2)(-) product ratio is significantly higher when (CS(2))(2)(-) is formed in the presence of water in the precursor gas mixture, even though the parent anion itself does not include H(2)O. On the other hand, an abrupt decrease in the above product ratio is observed upon the addition of solvent molecules (CS(2) or H(2)O) to the (CS(2))(2)(-) anion. Since the variation of this product ratio exhibits positive correlation with the relative intensity of the photoelectron band assigned to the C(2v) ((2)B(1)) covalent structure of C(2)S(4)(-) by Habteyes et al. [J. Phys. Chem. A 112, 10134 (2008)], this structure is suggested as the primary origin of the C(2)S(2)(-) and S(2)(-) photoproducts. The switching of the fragmentation yield from C(2)S(2)(-) and S(2)(-) to other products upon solvation is ascribed to the diminished presence of the C(2v) ((2)B(1)) dimer-anion structure relative to the CS(2)(-) based clusters. This population shift is attributed to the more effective solvation of the latter. The CS(2)(-) based clusters are suggested as the origin of the S(-) photoproduct, while CS(3)(-) is formed through the secondary S(-) + CS(2) intracluster association reaction.