The intermolecular potential and its angular dependence for two H2 molecules

The potential energy surface in the non-reactive region has been determined theoretically for the H₂-H₂ system. The procedure consists of a non-orthogonal configuration interaction calculation using the individual SCF orbitals of the separate molecules. The potential function is expressed as a 5-term sum of Legendre functions, and analytical expressions are given for the R dependence of the terms. The calculated depth of the spherically averaged Van der Waals well is -2·96 meV, which is in essentially complete agreement with the experimental value of -3·00 meV. the position of the minimum is at 3·49 Å both theoretically and experimentally. The value of C ₆ for dispersion forces obtained in this calculation is 12·97 a.u.