Ionization dynamics of the branched water cluster: A long-lived non-proton-transferred intermediate

The proton transfer (PT) reaction after water cluster ionization is known to be a very fast process occurring on the 10-30 fs time scale. In the present study, the ionization dynamics of the branched water tetramer (H2O)(4) were investigated by means of a direct ab initio molecular dynamics (AIMD) method to elucidate the time scale of PT in the water cluster cation. A long-lived non-proton-transferred intermediate was found to exist after the ionization of the branched-type water cluster. The lifetimes of the intermediate were calculated to be ca. 100-150 fs. PT occurred after the formation of the intermediate. The structure of the intermediate was composed of a symmetric cation core: H2O-H2O+-H2O. The broken symmetry of the structure led to PT from the intermediate. The reaction mechanism is discussed based on the theoretical results. (C) 2016 Elsevier B.V. All rights reserved.