Symmetric H3: A Semiempirical and <i>Ab Initio</i> Study of a Simple Jahn–Teller System

Abstract

Semiempirical and multiconfiguration ab initio results for the potential energy of H3 are used to obtain a detailed description of the potential-energy surface in the region of interest for the Jahn–Teller problem. Topographical properties of truncated perturbation expansions of the potential-energy function about the D3h minimum are compared with those of the complete semiempirical contour map; six symmetric dissociation “troughs” are found in the complete semiempirical surface, in contrast to three stable basins in the second-order surface and three dissociative troughs in the third-order surface. The relationships among the various parts of the complete three-dimensional H3 potential-energy hypersurface are discussed and illustrated by means of a single compact diagram. A convenient matrix-projection method for identifying normal-mode coordinate and electronic wavefunction partners associated with degenerate representations is discussed in an appendix.