Calculations on the HCl–Ar van der Waals complex

Abstract

Previously determined anisotropic intermolecular potentials for HCl–Ar are tested for comparison with the recent molecular beam resonance experiments on the van der Waals complexes. The Schrödinger equation for the coupled rotational and vibrational motion of the complex is solved accurately by a close coupling method. Energy levels, and expectations of the dipole moment, cosϑ, and cos2ϑ, where ϑ is the Ar–HCl center of mass-H angle, have been computed for the lower states of 40Ar complexes with H35Cl, H37Cl, D35Cl, and D37Cl. Rotational and centrifugal distortion constants were also computed for the lowest level. The assignment of the angle ϑ is discussed, and our results support the acute choice (i.e., H on the average between the Cl and Ar nuclei). The shift in angular expectations with HCl isotope distinguishes between the potentials tested here, and comparison with the experiments suggests that the true potential has an absolute minimum near ϑ=0°. However, none of the available potentials fits both the scattering data and the bound state spectroscopic data quantitatively. This demonstrates that the simultaneous analysis of scattering and bound state data constrains the potential much more than either alone.