Theoretical study on the reaction of the 2Δ ground state of TiS+ with CO2 in the gas phase

Two reaction channels of the 2Δ ground state of TiS+ with CO2 in the gas phase have been studied by using density functional theory at B3LYP/DZVP level: the O/S exchange reaction (TiS++CO2→TiO++COS) and the O-transfer reaction (TiS++CO2→TiSO++CO). It is found that the O/S exchange and O-transfer reactions starting from a common donor-acceptor intermediate (IM1) proceed via a four-center transition state (TS1) and a three-center transition state (TS2), respectively. The activation barriers of the two reaction channels are 3.1 and 57.8 kcal/mol, respectively, and it implies that the O/S exchange reaction is much more energetically favorable than the O-transfer reaction, which is in line with the experimental observations. The bonding properties of the stationary points involved in the O/S exchange reaction has been examined and discussed on the basis of the NBO analysis.