Prediction of fragment rotational quantum state distributions in molecular photodissociation processes: HOCl + hv → OH ( j) + Cl

Abstract

The objective of this Letter is to emphasise the importance of using the correct angular momentum selection rules and angular momentum coupling algebra when computing fragment rotational quantum state distributions in molecular photodissociation processes. Because the effort required for the computation of the quantum molecular dynamics of a dissociating polyatomic molecule increases significantly with increasing total angular momentum quantum number J, it has become common place to treat both the initial and final state in a polyatomic photodissociation process as possessing zero total angular momentum (i.e. J= J′=0). Using the example of the photodissociation of HOCl we show that such a treatment may lead to an incorrect rotational quantum state distribution of the photofragments. The computations and theory are based on a time-dependent quantum dynamical treatment of the problem. The normal approximation ( J= J′=0) is shown to lead to an incorrect estimation of the total photodissociation cross section.