Charge Exchange of Highly Charged Ions at Low Energy

A brief review is given of recombination processes of highly charged ions in typical astrophysical plasmas. The physical conditions are examined, under which recombination by charge exchange with neutral hydrogen and helium is the dominant recombination mechanism. The basic features of the charge exchange process involving highly charged ions are analysed in the framework of the molecular model of atomic collisions. Particular attention is devoted to the determination of the relevant potential energy surfaces of the molecular system by model potential methods. These methods are specially advantageous for ions with charge q > 2, when capture occurs primarily into excited states. The collision dynamics are treated by a quantum mechanical formalism. The resulting scattering equations are solved by first transforming to a diabatic representation. Typical results for charge exchange in C +4 /H and N +3 /H collisions are presented in the energy range 0.01-500 eV. The comparison with the recent experimental data is very satisfactory. On the basis of these results, a discussion is given of the successes and the shortcomings of the molecular model.