Photodestruction spectroscopy of carbon disulfide cluster anions (CS₂)^-_n n = 1-4: Evidence for the dimer core structure and competitive reactions of the dimer anion

Photodestruction spectra of carbon disulfide cluster anions, (CS₂)^-_n, n = 1-4, have been measured with a time-of-flight mass spectrometer coupled with an optical parametric oscillator. The spectra of all the cluster anions of n ≥ 2 were found to exhibit a similar absorption band peaking at 1.6-1.8 eV, suggesting that a C₂S^-₄ core is involved in the cluster anions. Photon energy dependence of competition between electron detachment and dissociation of the dimer anion was also observed. It was found that there is a reaction channel of the dimer anion producing C₂S^-₂ and S₂, as well as the ordinary dissociation into CS^-₂ and CS₂. The most stable form of the dimer anion was investigated by ab initio calculations at the unrestricted Hartree-Fock/6-31+G* level, showing that the stable form involves covalent C-C and S-S bonds. Reaction mechanisms are discussed on the basis of electronic symmetries of the parent and the fragments.