Atom-spherical top van der Waals complexes: A theoretical study

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Abstract
The theory of the vibration‐rotation states of atom‐spherical top van der Waals complexes is developed. The exact close‐coupled equations are closely analogous to those encountered in atom+spherical top scattering. The structure of the coupled equations is investigated, and close‐coupling calculations of the bound states of Ar–CH4 are presented for two different intermolecular potentials. The role of symmetry in the complex is discussed, and the energy levels are interpreted using a model in which the CH4 molecule undergoes hindered rotation in the field of the Ar atom. Correlation diagrams are presented, showing how the free‐rotor levels are converted into near‐rigid vibrational energy levels as the anisotropy of the intermolecular potential increases. The effect of higher‐order anisotropic terms is investigated, and correlation diagrams are given for complexes of tetrahedral, octahedral, and icosahedral molecules. The role of monomer vibrational angular momentum is investigated.