Theoretical studies of van der Waals molecules: the H2-H2dimer

The authors report calculations of the energy level structure of the H 2 -H 2 dimer in which the coupled equations have been numerically integrated. The R-matrix propagator and de Vogelaere algorithms have been used, and their respective convergence properties are briefly discussed. The convergence of the eigenvalues with respect to the size of the rotational basis set is also illustrated. Satisfactory numerical agreement is found with calculations based upon the secular equation method. Three independent ab initio potentials are studied. The recent CI potential of Meyer and Schaefer (1983) and Schaefer and Liu (1983) is found to give the best agreement with spectroscopic measurements, although a small shift of the position of the isotropic potential minimum is indicated.