A study of the rotational state dependence of predissociation of a polyatomic molecule: The case of ClO2

Abstract

This paper reports extensive measurements of the linewidths of rotational transitions in the à 2A2←X̃ 2B1 absorption of ClO2. It is found that: (1) The rate of predissociation is independent of the state of rotation of the initially excited molecule, (2) the rate of predissociation depends on the spin state prepared, being greater for the F1(J = N+1/2) state than for the F2(J = N−1/2) state, (3) for v1<3 the rate of predissociation from the states (v100) is independent of v1, but for v1≳3 the rate increases with v1, and (4) the bending mode is a promoting mode for the predissociation. It is argued that spin–orbit coupling is the dominant interaction between the prepared 2A2 state and the intermediate manifold in this indirect predissociation. Analysis of a model of this process leads to the prediction that, if the prepared and intermediate states have nearly the same geometry, whether the intermediate state is real or nascent, the rate of predissociation should be independent of initial rotational state. Furthermore, it is suggested that the spin–rotation interaction mixes the F1 and F2 states; using a two state analysis, the predicted ratio of rates of dissociation G(F1)/G(F2) = 1.2 is in qualitative agreement with that observed, and the lack of dependence of the ratio on N explained.