Radiative charge transfer in collisions of He++ ions with H(1s) atoms

Total cross sections for radiative charge transfer during collisions of He ions with H(ls) atoms leading to He+(ls) and H+ ions have been calculated at center of mass energies ranging from .1 to 1 eV. Since it is known from coupled-states calculations that non-adiabatic coupling effects are small at these energies, the problem is formulated in the adiabatic approximation where the 2pa molecular state is represented by an optical model potential. In this treatment, the radiative decay of the 2pa state of the HeH++ molecule is described by the imaginary part of the optical potential, which incorporates the 2pa - Isa transition rate (Einstein A coefficient). This transition rate for fixed intemuclear separations was calculated using ab initio wavefunctions of the HeH++ molecule For energies in the range where penetration of the centrifugal barrier is unimportant (E ^ 1 eV), cross sections were estimated via the JWKB approximation. At lower energies, the effect of tunneling is more important, and resonances associated with the predissociating states of the HeH++ molecule will dominate the structure in the cross sections. At these energies, cross sections are calculated by integrating the radial equation using the Numerov algorithm. The calculated cross sections vary from 4x1 cm at .1 eV to 1.4x1 cm at 1 eV. The radiative contribution to the total charge transfer cross section probably dominates at energies below 5 eV