Radiative and nonradiative charge transfer inHe++H collisions at low energy

Abstract

We report the calculated cross sections for the removal of ${\mathrm{He}}^{+}$ ions in collisions with hydrogen atoms for the collision energy range between 0.01 meV and 100 eV. Radiative association is the dominant mechanism at the low-energy extreme and for collision energies above 10 meV radiative charge transfer is dominant. Above 8 eV the radiative processes are negligible, and direct charge transfer is the primary removal mechanism. Using a quantum-mechanical method, we obtain the spectrum of the emitted radiation for the radiative charge transfer process at several collision energies. The emission spectrum has a main peak at wavelengths near 113 nm, which corresponds to the energy difference between the A ${}_{}{}^1{}_{}{}^{}\Sigma _{}^{+}{}_{}{}^{}$ and $X^1$ ${\Sigma }^{+}$ states of the molecular ion ${\mathrm{HeH}}^{+}$ at large internuclear distances. At higher collision energies, significant contributions to the emission spectra occur at shorter wavelengths, and distinct peaks appear. We interpret these peaks as a result of orbiting in the outgoing channel.