Alternative decoupled representations for the dynamics of van der Waals molecules: a test for the He, Ne-O2 systems

The simple dynamical process in which a diatomic molecule, treated as a rigid rotor, is bound to a rare-gas atom like He or Ne and is allowed to decay through dynamical internal energy redistribution is studied in detail via different decoupled representations of the total wavefunctions. By using realistic anisotropic intermolecular potentials and considering the process at the quantum level, four possible alternative pictures are analysed and their estimates of metastable-state energies and widths compared with rigorous close-coupled (CC) calculations. The comparison shows rather clearly that different pictures appear as more reliable, depending on the mass of the rare gas, the anisotropy of the interaction and the rotational-energy content of the molecular fragment. In all cases, however, our calculations indicate that, for such weakly interacting species, all present decoupling models already produce qualitative accord with the more rigorous, and expensive, CC calculations.