The role of the [Btilde]-[Xtilde] conical intersection in the photodissociation of water

Abstract

Non-adiabatic quasi-classical trajectories have been carried out on the [Btilde]-[Xtilde] ¹ A′ two-valued surface of H₂O using initial conditions which are appropriate to photodissociation via the [Btilde] 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 [Btilde]-Ã non-adiabatic process.