The role of the B˜-X˜conical intersection in the photodissociation of water

Non-adiabatic quasi-classical trajectories have been carried out on the B˜-X˜1A' two-valued surface of H2O using initial conditions which are appropriate to photodissociation via the B˜state. Two models have been used. One of these involves surface hopping between adiabatic surfaces and the other integrates the electronic density matrix in a diabatic basis along a classical trajectory. The results of the two are in broad agreement. The majority of OH fragments are formed in the OH(2Π) state which is consistent with experimental findings. Approximately 10 per cent of trajectories lead to O(1D) + H2. The majority of OH(2Σ+) is produced in high rotational states of v = 0, which is also confirmed by experiment. However, the calculations predict large populations of high vibrational states of OH(2Π) which disagrees with experiment. For this reason it is likely that OH(2Π) is mainly produced by the alternative B˜-Ã non-adiabatic process.