ATOM-SPHERICAL TOP VAN-DER-WAALS COMPLEXES - A THEORETICAL-STUDY

The theory of the vibration-rotation states of atom-spherical top van der Waals complexes is developed. The exact close-coupled equations ar e closely analogous to those encountered in atom+spherical top scatter ing. 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 mo del in which the CH4 molecule undergoes hindered rotation in the field of the Ar atom. Correlation diagrams are presented, showing how the f ree-rotor levels are converted into near-rigid vibrational energy leve ls as the anisotropy of the intermolecular potential increases. The ef fect of higher-order anisotropic terms is investigated, and correlatio n diagrams are given for complexes of tetrahedral, octahedral, and ico sahedral molecules. The role of monomer vibrational angular momentum i s investigated.