Rotational and angular distributions from photodissociations. III. Effects of dynamic axis switching in linear triatomic molecules

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Abstract
An analysis is presented of the effects of dynamic axis switching on the three-dimensional quantum mechanical theory of photodissociations of linear triatomic molecules. The dynamic axis switching phenomenon arises from the fact that there are small deviations of the orientation of the diatomic fragment axis from that of the equilibrium triatomic molecule axis in the initially bound state of the molecule. While these deviations vanish on the average, the dynamic axis switching is shown under certain circumstances to alter significantly the calculated rotational, orbital angular momentum and angular distributions from the results of the previous work in which these small deviations are ignored. The dynamic axis switching is demonstrated to be important for determining the proper partitioning of the triatomic initial state rotational angular momentum (J) into nascent diatomic rotational angular momentum and orbital angular momentum of the atom about the diatom. Thus, the dynamic axis switching effect vanishes for J = 0. The effects of this dynamical axis switching transformation are shown to be particularly important for dissociations involving heavy atomic fragments, with lighter atomic fragments giving a smaller effect. The correspondence is established between these quantum mechanical results and those obtained classically. Illustrative calculations are provided of the rotation–bending factor contribution to rotational energy and state resolved angular distributions in HCN and ICN photodissociation. Bending vibrations influence the angular distributions such that a state averaged distribution produces a preferred off-axis recoil direction which can be related to the mean square bending amplitude in the initial bound state.