Charge Exchange at Relativistic Energies

Abstract In ion-atom collision theory relativistic effects enter from two directions. If the nuclear charges ZA or Z8 are sufficiently large, the mean velocity of an electron in an atomic bound state (ve = Z/n) can become comparable with the velocity of light c. Accordingly relativistic corrections, which are negligible for small Z, rxZ ≤ 0.1, where rx is the fine structure constant, become significant for large Zand theatomic or molecular orbitals employed must be based on solutions of the single- or two-centre Dirac equation, or approximations to these. A different source of relativistic effects arises when the collision velocity is large compared with c, the velocity of light. Relativistic kinematics must then be employed, and, in addition, even for small values of ZA and Z8, relativistic atomic orbitals must be used since the momentum distribution of the bound electron, on which high-energy charge exchange depends explicitly, is very different in the relativistic and non-relativistic cases.