Rotational state specific dissociation dynamics of D2O via the (C)over-tilde electronic state

The rotational state resolved photodissociation dynamics of D2O via the C state has been investigated using the D-atom Rydberg tagging time-of-flight technique, with a tunable vacuum ultraviolet photolysis light source. The photodissociation action spectrum of the D2O (C) over tilde <-(X) over tilde (3p(z) <- 1b(1)) band has been recorded. The linewidths of rotational transitions have been determined by the Lorentzian profile simulation. Product kinetic energy distributions and angular distributions for individual rotational lines have been measured. From these distributions, the internal state distributions of the OD radical product as well as the state resolved angular anisotropy parameters for each rotational transition have been obtained. The dramatic variation of the OD product state distributions from different rotational excitations has been observed. These results suggest that there are two distinctive coupling channels from the (C) over tilde state to the lower electronic states: homogenous electronic coupling to the (A) over tilde(B-1(1)) state, resulting in a vibrationally hot OD(X (2)Pi) product and Coriolis-type coupling between the (C) over tilde(B-1(1)) state and the (B) over tilde((1)A(1)) state. Through the second mechanism, OD(X (2)Pi) as well as OD(A (2)Sigma(+)) products are produced. The OD(X (2)Pi) products are mainly populated in the vibrationally cold but extremely rotationally excited states. The comparison between the D2O and H2O results illustrates that the (C) over tilde(B-1(1)) -> (B) over tilde((1)A(1)) pathway is relatively larger in the D2O photodissociation as a consequence of the isotopic effect. (C) 2010 American Institute of Physics. [doi:10.1063/1.3457942]