Rotational state specific dissociation dynamics of HOD → H + OD via two-photon excitation to the C̃ electronic state.

The dissociation dynamics of HOD via two-photon excitation to the C̃ state have been investigated using the H-atom Rydberg tagging time-of-flight (TOF) technique. The H-atom action spectrum for the C̃ ← X̃ transition shows resolved rotational structure. Product translational energy distributions and angular distributions have also been recorded for the H + OD channel for three excited levels each with k(a)′ = 2. From these distributions, quantum state distributions and angular anisotropy parameters (β2 and β4) for the OD product were determined. These results are consistent with the nonadiabatic predissociation picture illustrated in the one-photon dissociation process for H2O. The heterogeneous dissociation pathway via Coriolis coupling is the dominant dissociation process in the present study. A high proportion of the total available energy is deposited into the rotational energy of the OD product. The anisotropic recoil distributions reveal the distinctive contributions from the alignment of the excited states and the dissociation process. Comparisons are also made between the results for HOD and H2O via the equivalent rotational transitions. The OH bond energy, D(o)(H−OD), of the HOD molecule is also determined to be 41283.0 ± 5 cm(-1).