Charge exchange in collisions of beryllium with its ion

Abstract

Close-coupling calculations of the resonance and near resonance charge exchange in ion–atom collisions of Be⁺₂ at low and intermediate energies are presented. Accurate ab initio calculations are carried out of the Born–Oppenheimer potentials and the non-adiabatic couplings that are due to the finite nuclear masses and drive the near resonance charge exchange. We show that the near resonance charge exchange cross section follows Wigner's threshold law of inelastic processes for energies below 10⁻⁸ eV and that the zero temperature rate constant for it is 4.5 × 10⁻¹⁰ cm³ s⁻¹. At collision energies much larger than the isotope shift of the ionization potentials of the atoms, we show that the near resonance charge exchange process is equivalent to the resonance charge exchange with cross sections having a logarithmic dependence. We also investigate the perturbation to the charge exchange process due to the non-adiabatic interaction to an electronic excited state. We show that the influence is negligible at low temperatures and still small at intermediate energies despite the presence of resonances.