Proton-Hydrogen-Atom System at Large Distances. Resonant Charge Transfer and the 1sσg-2pσu Eigenenergies of H2+
The resonant charge-transfer reaction of a proton with a hydrogen atom is evaluated in the adiabatic approximation. Previous calculations of this cross section have used various approximations to the energy difference between the 1sσg and 2pσu states of the hydrogen molecule ion H2+. This approximation is removed by solving the H2+ Schrödinger equation for the eigenparameters required in addition to those previously available in the literature. The resulting energy differences, found for internuclear separations of R<=40.0a0, are used to test the accuracy of large R estimates based on quasiclassical (WKB) and asymptotic arguments. The charge-transfer cross section calculated with the eigenergies is found to be, at most, a few percent different from earlier results based on approximate energy differences. Firsov's approximation and a recent modification by Smirnov are shown to be highly accurate when used with the eigenenergies.