Rotational Properties Associated with the Heitler–London Model of H2

Abstract

The first‐order WBK approximation has been used to determine rotational constants $B_{\upsilon }$ and $D_{\upsilon }$ for the Heitler–London (HL) model of the H₂ ground electronic state. Near‐equilibrium characteristics of $B_{\upsilon }$ and $D_{\upsilon }$ are discussed briefly in terms of the potential expansion about $r_e$ . Over‐all, the HL and experimental $B_{\upsilon }$ curves have nearly the same shape. The HL $B_{\upsilon }$ curve has negative curvature at all $\upsilon$ converging at a slightly slower rate than the experimental curve at high $\upsilon$ . This slower convergence is associated with the ${\text{1\hspace{0.17em}/\hspace{0.17em}r}}^2$ factor used in defining $B_{\upsilon }$ . The HL $D_{\upsilon }$ 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 $B_{\upsilon }$ and $D_{\upsilon }$ values.