The state-to-state photodissociation dynamics of HOD(Ã)

HOD, rotationally state selected in the third and fourth OH stretching overtone $\text{(|04〉,}$ $\text{|05〉)}$ levels, has been photodissociated via the à state at $\mathrm{\lambda \simeq }$ 288 nm. In accord with previous studies, H + OD is the dominant dissociation channel, with the yield of OH photofragments being below the detection limit in both sets of experiments. Model Franck-Condon calculations suggest that the OD photofragment rotational state distributions, determined by OD$(\mathrm{A-X})$ laser induced fluorescence ( LIF ), reflect primarily the rotational and zero-point bending motions in the selected rovibrational state of HOD$(\mathrm{X̃}\mathrm{).}$ However, in contrast to the state selected photodissociation of H${}_2$ O, the OD rotational distributions from HOD also reveal the influence of a small exit channel torque, which is enhanced in the photodissociation of the deuterated molecule by the shift in the OD centre-of-mass relative to that in OH. A modified Franck-Condon model, which accounts approximately for this modest impulsive torque, qualitatively reproduces the observed behaviour.