Phosphorous disulfide and its ions in the electronic ground state: A gas phase theoretical study

Ab initio molecular orbital theory and density functional theory calculations were performed on the electronic ground states of the open-shell PS₂ molecule and its singly charged ions. A comparison of the optimized molecular structures indicates as the stepwise one-electron reduction of the PS₂/⁺ ion, to yield PS₂ and PS₂/^-, provokes a symmetric elongation of both PS bonds along with a bending of its linear equilibrium geometry. The ionization potential (IP), adiabatic electron affinity (EA(ad)), and atomization energy (AE) of the open-shell PS₂ molecule were calculated at different levels of theory. The following values were obtained at the more realistic UMP4SDTQ/6-311 +G(3df)//UHF/6-311 +G(3df) level of theory: IP = 8.32 eV, EA(ad) = 3.03 eV and AE = 12.40 eV. At the same level of theory, the calculated vertical detachment energy (VDE) of the PS₂/^- anion is 3.22 eV. The donor-acceptor complexes formed in the gas-phase upon interaction of either one or two ammonia molecules with PS₂/⁺ were also investigated. The calculated gas-phase binding energies indicate that the formation of the bis- adduct is favored over that of the mono-adduct by a binding energy gain of about 20 kcal/mol. (C) 2000 Elsevier Science B.V.