Photolysis of HOBr and DOBr at 266 nm: OH and OD product-state distributions

The OH and OD rotational and vibrational product-state distributions have been recorded following the 266 nm photolysis of HOBr and DOBr, respectively, in a molecular beam. The photodissociation dynamics are similar to those observed for HOCl. The OH and OD distributions are rotationally cold and, for almost all of the states investigated, Gaussian in shape. Preferential population of the OH (or OD)2Π3/2 spin–orbit state was observed, together with a strong preference for the Π(A′)Λ-doublet levels. The alignment, β2o(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 was observed in the first excited vibrational state, with a similar rotational distribution to the OH (v= 0) products. The OD product distributions from DOBr were found to be sensitive to the molecular-beam expansion conditions with a bimodal distribution obtained for the colder expansions.The photodissociation is consistent with excitation of a non-bonding electron to a σ antibonding orbital which promotes rapid and direct bond fission via an upper state of A′ symmetry.