D.M. McSherry

New studies of the mechanism of electron emission at zero degrees in collisions of 100 KeV protons wirth H2 and He

Measurements of double differential cross sections for electron emission at zero degrees arising from collisions of 100 keV protons with H2 and He have been carried out. Calculations based on a continuum-distorted-wave eikonal-initial-state model have also been carried out and shown to provide a good description of the measurements. In addition, classical-trajectory Monte Carlo calculations have been employed to illustrate the evolution of electron emission at different times during the collision. The present measurements, which use a well defined gas target, provide no evidence of the existence of a significant saddle-point ionization mechanism at the energy considered.

Ion-atom /neon - calculation of ionization cross sections by fast ion-impact for neutral target atoms ranging from lithium to neon

The program presented calculates the total cross sections, and the electron energy spectra of the singly and doubly differential cross sections for the single target ionization of neutral atoms ranging from lithium up to and including neon. The code is applicable for the case of both high and low Z projectile impact in fast ion-atom collisions. The theoretical descriptions provided for the program user are based on two quantum mechanical models which have proved to be very successful in the study of ionization in ion-atom collisions. These are the continuum-distorted-wave (CDW) and continuum-distorted-wave eikonal-initial-state (CDW-EIS) approximations respectively.

Analytically continued generalized continuum distorted waves

The continuum distorted-wave eikonal-initial-state (CDW-EIS) theory of Crothers and McCann (Crothers D S F and McCann J F 1983 J. Phys. B: At. Mol. Phys. 16 3229) used to describe ionization in ion–atom collisions is generalized (G) to GCDW-EIS, to incorporate the azimuthal angle dependence into the final-state wavefunction. This is accomplished by the analytic continuation of hydrogenic-like wavefunctions from below to above threshold, using parabolic coordinates and quantum numbers including magnetic quantum numbers, thus providing a more complete set of states. At impact energies lower than 25 keV u−1, the total CDW-EIS ionization cross section falls off, with decreasing energy, too quickly in comparison with experimental data by Crothers and McCann. The idea behind and motivation for the GCDW-EIS model is to improve the theory with respect to experiment, by including contributions from non-zero magnetic quantum numbers. We also therefore incidentally provide a new derivation of the theory of continuum distorted waves for zero magnetic quantum numbers while simultaneously generalizing it.

Magnetically quantized continuum distorted waves

A new derivation of continuum distorted-wave theory is presented. It is generalized to magnetically quantized continuum distorted waves. The context is analytic continuation of hydrogenic-state wave functions from below to above threshold, using parabolic coordinates and quantum numbers including m the magnetic quantum number. This continuation applies to excitation, charge transfer, ionization, and double and hybrid events for both light- and heavy-particle collisions. It is applied to the calculation of double-differential cross sections for the single ionization of the hydrogen atom and for a hydrogen molecule by a proton for electrons ejected in the forward direction at a collision energy of 50 keV and 100 keV respectively.

Ejected electron spectroscopy: Ionization in ion-atom collisions

The continuum-distorted-wave eikonal-initial-state (CDW-EIS) approximation has had much success describing the single ionization of a bare atom by ion impact within the non-perturbative regime [Proc. R. Soc. Lond. A. 452 175–184 (1996)]. This model is first order in a distorted wave series incorporating an eikonal phase distortion in the initial state and a continuum-distorted-wave in the final state. The latter of these accounts for the ejected electron travelling in the presence of two long ranged Coulomb potentials. The single ionization of multielectron atoms shall be discussed, with particular emphasis on heavier targets such as neon and argon. A comparison will be made with other available theoretical models and experimental data.