Near Resonance Charge Exchange in Ion-Atom Collisions of Lithium Isotopes

Collisions of ions and atoms of Li-6 and Li-7 are explored theoretically over a wide range of energy from 10(-14) to 1 eV. Accurate ab initio calculations are carried Out of the Born-Oppenheimer potentials and the nonadiabatic couplings that are responsible for the near resonance charge exchange. Scattering studies show that the calculated charge exchange cross section follows Wigner's law for inelastic processes for energies below 10(-10) eV and that the zero temperature rate constant for it is 2.1 x 10(-9) cm(3) 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 on energy. A comparison with the Langevin model at intermediate energies is also presented.