Potential-Energy Surface for H3

An a priori variational calculation of the H3 potential-energy surface has been made with complete configuration-interaction wavefunctions formed from optimized-exponent basis sets of six orbitals (1s, 1s′, on each nucleus) and 15 orbitals (1s, 1s′, 2px, 2py, 2pz, on each nucleus). Linear (180°) and nonlinear (150°, 120°) geometries were examined for a wide range of internuclear distances with particular emphasis on the minimum-energy path for each angle. The 15-orbital set yielded a linear-symmetric saddle point at an internuclear distance of 1.765 a.u. with an energy 11 kcal/mole above that of a corresponding calculation for an isolated hydrogen atom and hydrogen molecule. The H3 surface, details of which are presented in terms of tables, least-squares fits, and contour maps, is found to be similar in form to a semiempirical surface which has been used in quasiclassical analysis of the (H, H2) exchange reaction. However, there are quantitative differences, whose significance can be ascertained only by more refined a priori treatments and new dynamical calculations.