Photodissociation dynamics of H2O and D2O via the D̃(1A1) electronic state

Photodissociation dynamics of H2O and D2O via the state by one-photon excitation have been investigated using the H/D atom Rydberg tagging time-of-flight technique. The TOF spectra of the H/D-atom product in both parallel and perpendicular polarizations have been measured. Product translational energy distributions and angular distributions have been derived from TOF spectra. By simulating these distributions, quantum state distributions of the OH/OD product as well as the state-resolved angular anisotropy parameters were determined. The most important pathway of H2O/D2O dissociation via the state leads to highly rotationally excited OH/OD(X, v = 0) products, while vibrationally excited OH/OD products with v ≥ 1 comprise only one third of the total OH/OD(X) population. The branching ratios of OH(A)/OH(X) and OD(A)/OD(X) have also been determined, 1.0/3.0 for H2O at 122.12 nm and 1.0/2.2 for D2O at 121.95 nm, which are reasonably consistent with the values predicted by the previous theory.