Activation of CO2 in Photoirradiated CO2-H2O Clusters: Direct Ab Initio Molecular Dynamics (MD) Study

Carbon dioxide (CO2) is one of the stable and inactive molecules that contribute to greenhouse gases. The development of new reactions of CO, activation, chemical fixation, and conversion is a very important issue. In this report, the reactions of CO2-H2O binary clusters were investigated using a direct ab initio molecular dynamics (AIMD) method to find a new reaction of CO, activation. Clusters composed of carbon dioxide and water molecules, CO2 (H2O)(n) (n = 2-5), were utilized as a model of the binary cluster. The reaction dynamics of [CO2 (H2O)(n)](+) following the ionization of parent neutral clusters were also investigated. Two electronic states of [CO2(H2O)(n)](+) were examined for direct AIMD surfaces: [CO2(H2O)(n)](+) (ground state) and (CO2 ) + (H2O)(n) (excited charge transfer (CT) state). After the ionization of the clusters, a proton-transfer (PT) reaction occurred within the (H2O)(n)(+) moiety at the ground state, whereas the reactive HCO3 radical was formed at the CT state for OH addition to CO2+ : + CO2+(H2O)(n) -> HCO3 +H- (+)(H2O)(n-)(1). The mechanisms of the PT process and the HCO3 radical formation were discussed based on the theoretical results.