A non-adiabatic wave packet study of the post-collisional fragmentation of H2O

In a previous paper [1], we have carried out a wave-packet-propagation calculation to study the fragmentation of the water cation on the B̃ state. The initial condition of our calculation was a FranckCondon wave packet (FCWP), obtained by vertical ionization of the ground vibrational state of H2O. The calculation employed the GRID-TDSE package [2] modified in order to incorporate non-adiabatic transitions, to solve time-dependent Schrödinger equation. In that work we showed that the dissociation mechanism involves non-adiabatic transitions to the states à and X̃ . The transition B̃–à takes place in a few femtoseconds in the vicinity of the conical intersection (CI) between the corresponding potential energy surfaces. When the wave packet approaches the linear configuration, the states à and X̃ are degenerate and connected via a Renner-Teller coupling, which populates the ground state X̃ . The fragmentation can take place either through the energy transfer from the bending to the stretching motion in the à state, leading to the dissociation into OH+H+, or, after the Renner-Teller transition, leading to the dissociation into OH++H. A stringent test of the method is provided by the comparison with the photodissociation experiments of Harbo et al. [4], who measured the ratio between the cross sections for production of the fragments OH+H+ and OH++H in a crossedbeam experiment where H2O was irradiated with a 532 nm (2.33 eV) laser, obtaining