No abstract

We present a theoretical study of charge transfer in collisions of excited (n = 2, 3) hydrogen atoms with He + and in collisions of excited (n = 2, 3) helium atoms with H +. A combination of a fully quantum-mechanical method and a semi-classical approach is employed to calculate the chargeexchange cross sections at collision energies from 0.1 eV/u up to 1 keV/u. These methods are based on accurate ab initio potential energy curves and non-adiabatic couplings for the molecular ion HeH +. Charge transfer can occur either in singlet or in triplet states, and the differences between the singlet and triplet spin manifolds are discussed. The dependence of the cross section on the quantum numbers n and l of the initial state is demonstrated. The isotope effect on the charge transfer cross sections, arising at low collision energy when H is substituted by D or T, is investigated. Finally, the impact of the present calculations on models of laboratory plasmas is discussed.

The cross section for charge transfer in proton-helium collisions has been computed in the energy range from 10 eV/u up to 10 MeV/u. Four different methods (full quantal time-independent and time-dependent methods, molecular and atomic basis set semi-classical approaches) valid in different energy regimes have been used to calculate the partial and total cross section for single-electron capture. The results are compared with previous theoretical calculations and experimental measurements and the different theoretical methods used are shown to be complementary for describing the charge transfer reaction. A fit of the cross section, valid for collision energies from 10 eV/u up to 10 MeV/u is presented based on these results.