Theoretical studies of van der Waals molecules: the D2-D2dimer

The M80 potential energy surface of Meyer, Schaefer and Liu (1983) is used to obtain the bound-state energies of dimers of deuterium in both its ortho and para modifications. The quantum mechanical close-coupling equations have been solved by direct numerical integration. Scattering calculations have yielded the energies and widths of rotationally predissociating states of ortho-D 2 -ortho-D 2 . That some of these resonances have dual Feshbach/shape character is noted. The dimer structure accompanying the observed near-infrared S 1 (0) and Q 1 (0)+S 0 (0) spectra in ortho-deuterium, is modelled by treating the two D 2 molecules as distinguishable rigid rotors. The conclusions, that the 1974 measurements of McKellar and Welsh provide evidence both for rotational splitting and internal rotational predissociation, are examined in the light of new spectroscopic results.