Quantum state-selected photodissociation dynamics of H2O: Two-photon dissociation via the (C)over-tilde electronic state

The photodissociation dynamics of H2O via the (C) over tilde state by two-photon excitation has been investigated using the H atom Rydberg tagging time-of-flight technique. The rotational resolved action spectrum of the (C) over tilde <-(X) over tilde transition band has been measured. The line widths show a pronounced dependence on the parent rotational excitation in the (C) over tilde state. The quantum state resolved OH product translational energy distributions and angular distributions have also been obtained. By carefully simulating these distributions, quantum state distributions of the OH product as well as the state-resolved angular anisotropy parameters were determined. The experimental results confirm the variation of two competitive predissociation pathways. A heterogeneous predissociation channel is mediated by rotational coupling to the (B) over tilde (1)A(1) state associated with the a-axis (k(a)'), and a homogeneous pathway arises from purely electronic coupling to the (A) over tilde B-1(1) state. We have also obtained the branching ratios of the OH(X) and OH(A) products, and related these to the (C) over tilde ->(A) over tilde and (C) over tilde ->(B) over tilde pathways. The branching ratios display a strong k(a)' dependence. (C) 2010 American Institute of Physics. [doi:10.1063/1.3487736]