Proton angular distributions and highly differential cross sections for ionization of helium by proton impact

Abstract

The eikonal distorted-wave method is applied to single ionization in proton-helium collisions at laboratory energies of 300 keV, 500 keV, 1 MeV, and 3 MeV. The angular distributions of scattered protons agree well with recent experimental results, showing substantial improvement over the plane-wave Born approximation especially at large scattering angles e. The momentum distributions of the ejected electrons at fixed values of e are calculated. In particular, those of the electrons ejected mainly in binary proton-electron collisions are studied in detail. The momentum distributions of the recoil He+ ions at fixed values of e are also discussed by comparing with the results of recent coincidence measurements.At such small 6 at which the plane-wave Born and the eikonal distorted-wave approximations give nearly the same cross sections and are expected to be accurate, these approximations lead to average momenta of recoil ions significantly lower than the measured values.

Comparison of theoretical and absolute experimental fully differential cross sections for ion-atom impact ionization

“…This impact parameter treatment in conjunction with the neglect of the internuclear interaction at high impact energies is an excellent example of the right way to do theoretical physics if one is interested in electron spectra (Moshammer et al 1999) since the goal of theory should be to explain physical observations using the minimum amount of necessary physics. Nevertheless, these approximations are not valid for fully differential cross sections (or any cross section differential in projectile scattering angle -see Salin 1989, Fukuda et al 1991aand 1991b, Fang and Reading 1991, Rodríguez and Barrachina 1998, Schulz et al 2002. Therefore, in the present work, the internuclear interaction is included and the projectile motion is treated fully quantum mechanically.…”

Cold Target Recoil Ion Momentum Spectroscopy

“…In this regime the electron}recoil ion momentum exchange dominates. These transverse momentum exchange processes are well described by nCTMC calculations [51,58,159,160] as well as by quantum mechanical calculations in the Continuum Distorted Wave approach [157,158,161,162].…”

“…The scatter in the data represents the systematical error due to uncontrolled electric "elds in the cooled gas cell used in this experiment. Dashed line: two-body scattering of the projectile at the target nucleus, full line: nCTMC calculation [98] (see also [58]), these results are di!erent from the nCTMC results in [51], which were found to be in error (see [54]), dotted line: nCTMC folded with the target thermal motion at 30 K, dashed dotted line: Eikonal distorted wave calculation [157,158] (from [53]). Recent experiments with a supersonic gas-jet target by Weber et al [84] give evidence that the saturation energy of 10$5 meV at small scattering angles is at the upper limit of the error bart including the shift to higher energies due to the target thermal motion.…”

Dynamic mechanisms of He single ionization by fast proton impact

“…Plane-wave-Bornapproximation (PWBA) calculations [4] attributed this behavior as being due to the dominant contribution of projectiletarget-electron scattering (p-e) events to the difFerential cross section for 8 0.55 mrad, which is the maximum deflection angle for protons being scattered off a free electron at rest. The PWBA calculations were followed by classical [6], semiclassical quantum-statistical [7], as well as by quantum-mechanical approaches in the Born [8], the Glauber [9] and eikonal distorted wave (EDW) approximations [10]. They all include the interaction of the projectile with both the target electron and the target nucleus to calculate the projectile deflection.…”

“…They are relatively large since in this experiment an extended time window of 20 ps was necessary to measure the recoil-ion time of flight which ranges up to 7 ps (this has to be compared to a typical time resolution of about 6 ns in an experiment where the recoil ions are extracted by an electric field with a 4s olid angle and only their charge state is detertnined [4]). [9];~~~., EDW [10] approximation) and to the recoil ion p",j l4, experiment;, n-CTMC).…”