Rotational state specific dissociation dynamics of D_2 O via the C? electronic state

摘要

The rotational state resolved photodissociation dynamics of D_2 O 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 D _2 O C? X? (3 pz 1 b_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? state to the lower electronic states: homogenous electronic coupling to the ? (~1 B_1) state, resulting in a vibrationally hot OD (X Π2) product and Coriolis-type coupling between the C? (~1 B_1) state and the B? (~1 A _1) state. Through the second mechanism, OD (X Π2) as well as OD (A ~2∑+) products are produced. The OD (X Π2) products are mainly populated in the vibrationally cold but extremely rotationally excited states. The comparison between the D_2 O and H_2 O results illustrates that the C? (~1 B_1) → B? (~1 A _1) pathway is relatively larger in the D_2 O photodissociation as a consequence of the isotopic effect.