Rotational predissociation of the Ar⋅HCl van der Waals complex: Close-coupled scattering calculations

We report an extensive computational study of rotationally predissociating metastable states of the Ar⋅HCl van der Waals complex, using a highly realistic empirical intermolecular potential recently proposed by Hutson and Howard. The states are characterized by fully converged, close-coupled, scattering calculations. Resonance energies, widths, and partial widths are extracted by fitting the energy dependence of S matrices. Total angular momenta of 0 and 1 are studied, and the calculations span an energy range from 0 to 1400 cm−1. The resonance widths vary from <10−4 to ≳5 cm−1, and it is shown that the isolated narrow resonance approximation is of poor validity for the wider resonances. Comparison of the close-coupling results with approximate calculations enables assignment of approximate quantum numbers to the metastable states. Physical explanations are suggested for the strong trends in resonance parameters as a function of the intermolecular stretching, diatom rotation, and molecule-fixed angular momentum projection quantum numbers. A changeover from a near-molecule-fixed to a near-space-fixed coupling scheme, as angular momentum is increased, is clearly demonstrated. The results are of considerable relevance to the design of experiments and the development of approximate computational methods in this area.