PHOTOLYSIS OF HOBR AND DOBR AT 266-NM - OH AND OD PRODUCT-STATE DISTRIBUTIONS

The OH and OD rotational and vibrational product-state distributions h ave been recorded following the 266 nm photolysis of HOBr and DOBr, re spectively, in a molecular beam. The photodissociation dynamics are si milar to those observed for HOCl. The OH and OD distributions are rota tionally cold and, for almost all of the states investigated, Gaussian in shape. Preferential population of the OH (or OD) 2PI3/2 spin-orbit state was observed, together with a strong preference for the PI(A') LAMBDA-doublet levels. The alignment, beta0(2)(02), tends towards the limiting value of -0.5 at the highest N levels that could be observed. In contrast to the photolysis of HOCl, about 10% of the OH fragment w as observed in the first excited vibrational state, with a similar rot ational distribution to the OH(v = 0) products. The OD product distrib utions from DOBr were found to be sensitive to the molecular-beam expa nsion conditions with a bimodal distribution obtained for the colder e xpansions. The photodissociation is consistent with excitation of a no n-bonding electron to a sigma antibonding orbital which promotes rapid and direct bond fission via an upper state of A' symmetry.