1/R expansion for H2+: Calculation of exponentially small terms and asymptotics

The energy of any bound state of the hydrogen molecule ion H2+ has an expansion in inverse powers of the internuclear distance R of the form Rayleigh-Schroedinger perturbation theory (RSPT) gives the coefficients E/sup( N/) but is otherwise unable to treat the exponentially small series, which in part are characteristic of the double-well aspect of H2+. (Here n denotes the hydrogenic principal quantum number.) We develop a quasisemiclassical method for solving the Schroedinger equation that gives all the exponentially small subseries