Quantum state-selected photodissociation dynamics of H2O: two-photon dissociation via the C̃ electronic state

J Chem Phys. 2010 Oct 7;133(13):134301. doi: 10.1063/1.3487736.

Abstract

The photodissociation dynamics of H(2)O via the C̃ 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 C̃←X̃ transition band has been measured. The line widths show a pronounced dependence on the parent rotational excitation in the C̃ 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 B̃ (1)A(1) state associated with the a-axis (k(a)(')), and a homogeneous pathway arises from purely electronic coupling to the à (1)B(1) state. We have also obtained the branching ratios of the OH(X) and OH(A) products, and related these to the C̃→à and C̃→B̃ pathways. The branching ratios display a strong k(a)(') dependence.