Effects of isomer coexistence and solvent-induced core switchingin the photodissociation of bare and solvated (CS_2)_2-anions

摘要

The photodissociation of the (CS_2)_2 dimer anion, known to exist in the form of several electronicand structural isomers, has been investigated at 532, 355, and 266 nm. The observed anionicfragments are CS_2-and C_2S_at 532 nm, 2—, CS_3—S2—S-355 266 nm.In addition to the photon energy, the fractional yields of the photofragments depend on the ionsource conditions and solvation of the dimer anion. Specifically, the (C_2S_2 + S_2-)/ CS_productratio is significantly higher when (CS_2)_2-is formed in the presence of water precursor gasmixture, even though the parent anion itself does not include H_2O. On the other hand, an abruptdecrease in the above product ratio is observed upon the addition of solvent molecules (CS_2or H20)to the (CS_2)_2-anion. Since the variation of this product ratio exhibits positive correlation with therelative intensity of the photoelectron band assigned to the C_(2v)(~2B_1)covalent structure of C_2S_4 byHabteyes et al. [J. Phys. Chem. A 112, 10134 (2008)], this structure is suggested as the primaryorigin of the C_2S_2-and S_2 photoproducts. The switching of the fragmentation yield from C_2S_andS2— to other products upon solvation is ascribed to the diminished presence of the C_(2v)(~2B_1)dimer-anion structure relative to the CS_2 based clusters. This population shift is attributed to themore 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_2intracluster associationreaction.