Rotational Properties Associated with the Heitler–London Model of H2

Abstract

The first-order WBK approximation has been used to determine rotational constants Bυ and Dυ for the Heitler–London (HL) model of the H2 ground electronic state. Near-equilibrium characteristics of Bυ and Dυ are discussed briefly in terms of the potential expansion about re. Over-all, the HL and experimental Bυ curves have nearly the same shape. The HL Bυ curve has negative curvature at all υ converging at a slightly slower rate than the experimental curve at high υ. This slower convergence is associated with the 1 / r2 factor used in defining Bυ. The HL Dυ curve, like the corresponding experimental curve, rises rapidly in the vicinity of dissociation. Both increases are attributed to a breakdown in the approximation that treats the centrifugal reaction term as a perturbation of the rotationless problem. The reliability of the first-order WBK approximation is checked and found to lead to only slight errors in the Bυ and Dυ values.