Quasi-Molecular Interference Effects in Ion-Atom Collisions

Abstract

Publisher Summary A number of new fundamental phenomena have been discovered in atomic collision physics over the past ten years. One of these is quantum-mechanical phase interference between inelastic quasi-molecular channels. The coherent excitation of the inelastic quasi-molecular amplitudes and their interference result in an oscillatory structure in the energy dependence of the total cross sections of the inelastic scattering channels. This chapter reviews the experimental and theoretical studies where phase interference phenomena have been established and comprehensively investigated. The interference effects were first observed as a result of an investigation of spectral line emission originating during low-energy ion-atom collisions. The energy range of low-energy collisions is assumed to be comparable with the energetics of the outer-shell excitation for the atoms and single ions involved. In practice this means that the laboratory energy E of fast ions is less than 10 keV. Theoretical consideration of the interference effects follows the quasi-molecular approach to atomic collisions. According to this approach, the probability of an inelastic process and its dependence on the collision energy are determined by nonadiabatic transitions in a quasi-molecular system, i.e., dynamic processes in a two-atom molecule with changing internuclear separation. This chapter gives attention to experimental investigations where the phase interference of inelastic quasi-molecular amplitudes has been first observed and the qualitative interpretation has been given. The next section of this chapter deals with the studies of oscillatory structures of total cross sections of inelastic scattering processes. A new type of interference effect is discussed in next. This effect is responsible for regular oscillations in the degree of polarization of light emitted in atomic collisions. The importance of the interference phenomenon for atomic collisions is discussed in the final section of this chapter along with a brief review of recent atomic investigation where phase interference is found to be important.