Photodissociation of H2O and D2O in (B)over-tilde, (C)over-tilde, and (D)over-tilde states (134-119 nm).: Comparison between experiment and ab initio calculations

Rotational and vibrational state distributions have been measured for the OH/OD(A(2)Sigma(+)) fragment produced by the photodissociation of H2O/D2O at a set of wavelengths in the 133 - 119 nm range that lead to excitation of the (B) over tilde((1)A(1)) state, either directly or through particular absorption features of the (C) over tilde B-1(1) <-- (X) over tilde (1)A(1) and (D) over tilde (1)A(1) <-- (X) over tilde (1)A(1) Rydberg transitions. The experimental distributions are obtained from the A(2)Sigma(+) - X(2)Pi fluorescence spectra using a truncated single value decomposition method (TSVD). They are compared to distributions calculated in a complete three-dimensional quantum mechanical treatment by using two sets of diabatic potential energy surfaces obtained by Dobbyn and Knowles (DK) and by van Harrevelt and van Hemert (Leiden). The measured vibrational branching ratios seem to be better accounted for by the former and the rotational distributions by the latter. However, a more detailed analysis indicates that the DK surface would presumably account for the experiment if the room-temperature rotational distribution of the parent water molecule were introduced in the calculation. The experimental results are therefore interpreted as a confirmation of the more direct and shorter-lived trajectories favored by the DK surface.