Short-range interactions in ground state H2+ using fluctuation theory techniques

Fluctuation theory techniques are used to evaluate short-range interactions in ground state H2+ by calculating in a direct way small energy differences taken with respect to the ground state of the united atom He+. Appropriate coordinate transformation allows to obtain inner and outer Hermitean eigenvalue equations, which are then solved perturbatively in positive powers of the internuclear distance R choosing He+ as unperturbed problem. The separation constants are deduced from the regularity conditions on the functions. Next, the function endowed with the right symmetry is constructed by solving an integral equation in a perturbative way. A second-order approximation gives short-range interaction coefficients which are exact up to R5.