Coupled-State Treatment of Charge Transfer

Abstract

Publisher Summary This chapter discusses the concept of coupled-state treatment of charge transfer. Charge transfer in ion–atom collisions is a basic atomic collision process, also called charge exchange, electron capture, and electron transfer. The focus is on the bare nuclear projectile incident on a one-electron atom or ion. At projectile speeds on the order of the orbital speed of the target electron, charge transfer is typically significant, and competes with ionization and direct excitation as a mechanism for depleting the elastic channel. For proton–hydrogen collisions, “velocity” matching occurs for 25 keV projectiles; and at somewhat lower and higher energies, many intermediate states are potentially important during the collision, so coupled-state approaches are generally most appropriate. Such approaches have been extensively developed and applied in this so-called intermediate-energy range. Further, it is generally believed that at energies of at least about 100 eV/u the nuclear motion can be assumed to be classical; there the nuclear deBroglie wavelength is significantly smaller than the size of the atomic target. At such energies an impact-parameter approach is appropriate, and the projectile follows a definite trajectory, the position vector of the projectile nucleus relative to the assumed stationary target nucleus at a time, taken to be zero at the point of closest approach. At still higher energies the trajectory can be assumed to be rectilinear; this additional assumption, which is not essential is also discussed in the chapter.