Molecular treatment of charge exchange in H++Li collisions

Electron capture in proton-lithium collisions at centre of mass energies below 10 keV is examined in the PSS approximation using a model potential for the e+Li + interaction. It is assumed that the level H(n=2) is preferentially excited. Eigenvalues of the molecular Hamiltonian are found variationally, and radial and rotational coupling elements are calculated directly from these in prolate spheroidal coordinates. The coupling elements show strong dependence on the choice of coordinate system and have non-zero asymptotic limits. The authors use an adiabatic switching factor in the asymptotic region to ensure convergence of the cross sections. These are evaluated in the impact parameter approximation. Calculations involving both six and seven molecular states are performed. Radial coupling dominates the process at higher energies while rotational coupling is more important below 500 eV.