High-level ab initio calculations on the structures and relative stabilities of [O, P, H] systems and their cations

Abstract

Ab initio molecular orbital calculations at levels of theory beyond G2 have been used to study the structures, relative stabilities, ionization potentials and heats of formation of [O, P, H] neutral and cationic species, which are involved in the reactions of P + with water in the gas phase. OPH ( 3A″) and OPH + ( 2A′) are open-shell systems for which UMP theory is not reliable. Hence, their structures, as well as those of the other open-shell species were obtained at the QCISD (T)/6-311G (d, p) level. Possible shortcomings of the G2 theory were investigated by comparing G2 energies with those obtained at the QCISD (T)/6-311 + G (3df, 2p) level. The energies obtained indicate that the formation of the OPH + ( 2A′) molecular cation in the reaction of P + in its first excited state ( 1D) is exothermic and may play a significant role in the production of PO in interstellar media.