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Ionization Ion-Atom Collisions: Recoil-Ion Momentum Spectroscopy and Ejected Electron Spectroscopy

  • S. F. C. O’Rourke
  • W. Schmitt
  • R. Moshammer
  • J. Ullrich
  • B. S. Nesbitt
  • D. S. F. Crothers
Chapter
Part of the Physics of Atoms and Molecules book series (PAMO)

Abstract

In the last few years there has been a very intense effort to understand the process of single ionization in ion-atom collisions. Experiments in this field have followed largely along two main lines; recoil-ion momentum spectroscopy and ejected electron spectroscopy. Both techniques can address distinct features characterizing ionization processes in ion-atom collisions. At this stage it is essential to understand the complementary nature of both recoil-ion momentum spectroscopy and ejected electron spectroscopy. Each technique provides detailed information on the ionization mechanism which can serve as a most stringent test for theory. The aim of this paper is to discuss the non-perturbative quantum mechanical models used most commonly in the description of ion-atom ionization collisions. From the theoretical point of view the main difficulty is the representation of the final electronic state, where the ionized electron travels in the presence of two Coulomb potentials (target and projectile). Due to the long-range ionic tail of the Coulomb potential the ”free particle” cannot be represented by a plane wave. So far an exact solution to this problem has not been found. However an exact asymptotic form can be obtained exactly1,2 and the main objective of this paper is to review the continuum-distorted-wave3,4 (CDW) and continuum-distorted-wave eikonal-initial-state1,2 (CDW-EIS) models which at least satisfy the exact asymptotic conditions in the initial and final states. Both the approximations are based on distorted wave perturbation theory. The difference between CDW and CDW-EIS theory lies in the distortion of the initial state, which is a Coulomb wave in the former and an eikonal phase in the latter. First we will discuss the applicability of these models for kinematically complete experiments on target single ionization in ion-atom collisons which have been performed using the tecnique of recoil-ion momentum spectroscopy. The examples illustrated will include the pioneering experiments5,6,7 of 3.6 MeV/u Ni24+, Se28+, Au24+ and Au53+ ions on helium target atoms. Secondly we are interested in the electron spectroscopy method which allows investigations on the two-centre effects that influence electron emission. The strength of this particular experimental technique lies in its ability to measure the doubly differential cross sections (DDCS) as a function of the electron emission angle and energy. There are two distinct characteristics based on two-centre electron emission which can be easily identified in this spectrum. The first is electron capture into the projectile continuum (ECC mechanism). Here the DDCS shows a cusp at an electron velocity which matches the projectile velocity. The second is the binary encounter (BE) mechanism which can be identified as a peak, centred around an electron velocity which is twice the projectile velocity. It has also been suggested that another signature, called the saddle point emission mechanism8 arises from the possibility that the emitted electron is stranded on the the saddle point of the two-centre potential between the target ion and receding projectile. This mechanism leads to an electron distribution centred at a velocity close to half the projectile velocity. We consider the applicability of the CDW and CDW-EIS to predict these ionization features in the DDCS. The examples illustrated include the measurements from Lee et al9 of 1.5 MeV/u H+ and F9+ on helium and measurements from Shah et al10 of 50 keV H+ on H2 and 75 keV H+ on helium. We begin section 2 with a brief description of the essential equations for the various ionization cross sections. In section 3 we compare the theoretical calculations with the recoil-ion momentum spectroscopy and electron spectroscopy techniques. Finally we summarize our results in section 4.

Keywords

Differential Cross Section Single Ionization Doubly Differential Cross Section Projectile Velocity Binary Encounter 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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References

  1. 1.
    D.S.F. Crothers and J.F. McCann, Ionization of atoms by ion impact, J. Phys. B 16:3229, (1983).Google Scholar
  2. 2.
    P.D. Fainstein, V.H. Ponce and R. D. Rivarola, A theoretical model for ionization in ion-atom collisions. Application for the impact of multicharged projectiles on helium, J. Phys. B 21:287 (1988).ADSCrossRefGoogle Scholar
  3. 3.
    Di. Belkic, A quantum theory of ionization in fast collisions between ions and atomic systems, J. Phys. B 11:3529 (1978).ADSCrossRefGoogle Scholar
  4. 4.
    S.F.C. O’Rourke and D.S.F. Crothers, Single ionization of He by 3.6 MeV amu-1 Ni24+ ions, J. Phys. B 30:2443 (1997).ADSCrossRefGoogle Scholar
  5. 5.
    R. Moshammer, J. Ullrich, M. Unverzagt, W. Schmitt, P. Jardin, R.E. Olson, R. Mann, R. Dörner, V. Mergel, U. Buck and H. Schmidt-Böcking, Low-energy electrons and their dynamical correlation with recoil ions for single ionization of helium by fast, heavy-ion impact, Phys. Rev. Lett. 73:3371 (1994).ADSCrossRefGoogle Scholar
  6. 6.
    R. Moshammer J. Ullrich, H. Kollmus, W. Schmitt, M. Unverzagt and H. Schmidt-Böcking, C.J. Wood and R.E. Olson, Complete momentum balance for single ionization of helium by fast ion impact: Experiment, Phys. Rev. A 56: 1351 (1997).ADSCrossRefGoogle Scholar
  7. 7.
    W. Schmitt, R. Moshammer and J. Ullrich, private communication (1998).Google Scholar
  8. 8.
    V.D. Irby, T.J. Gay, J. Wm. Edwards, E.B. Hale, M. L. McKenzie and R.E. Olson, Projectile-charge dependence of ejected-electron spectra, Phys. Rev. A 37:3612 (1988).ADSCrossRefGoogle Scholar
  9. 9.
    D.H. Lee, P. Richard, T.J.M. Zouros, J.M. Sanders, J.L. Shinpaugh and H. Hidmi, Binary-encounter electrons observed at 0° in collisions of 1–2-MeV/amu H+, C6+, N7+, O8+, and F9+ ions with H2 and He targets, Phys. Rev. A 41:4816 (1990).ADSCrossRefGoogle Scholar
  10. 10.
    M.B. Shah, H.B. Gilbody, J. Geddes and K. Lozhkin, private communication (1998).Google Scholar
  11. 11.
    E. Clementi and C Roetti, Basis Functions and their coefficients for ground and certain excited states of neutral and ionized atoms Z ≤ 54 At. Data. Nucl. Data. Tables 14:177 (1974).ADSCrossRefGoogle Scholar
  12. 12.
    J. Ullrich, R. Moshammer, R. Dörner, O. Jagutzki, V. Mergel, H. Schmidt-Böcking and L. Speilberger, Recoil-ion momentum spectroscopy, J. Phys. B 30:2917 (1997).ADSCrossRefGoogle Scholar
  13. 13.
    P.D. Fainstein, V.H. Ponce and R.D. Rivarola, Two-centre effects in ionization by ion impact, J. Phys. B 24:3091 (1991).ADSCrossRefGoogle Scholar
  14. 14.
    S.F.C. O’Rourke, R. Moshammer and J. Ullrich, Longitudinal momentum distributions in single ionization of He by 3.6 MeV u-1 Se28+ ions, J. Phys. B 30:5281 (1997).ADSCrossRefGoogle Scholar
  15. 15.
    V.D. Rodriguez, Y.D. Wang and C.D. Lin, Longitudinal momentum distributions in ionization of helium by fast, highly charged projectiles, J. Phys. B 28:L471 (1995).ADSCrossRefGoogle Scholar
  16. 16.
    Kh. Khayyat et al, Differential cross sections in antiproton-and proton-helium collisions, Phys. Rev. Lett (submitted) (1998).Google Scholar
  17. 17.
    L. Gulyás, P.D. Fainstein and A Salin, CDW-EIS theory of ionization by ion impact with Hartree-Fock description of the target, J. Phys. B 28:245 (1995).ADSCrossRefGoogle Scholar
  18. 18.
    S.F.C O’Rourke, M.B. Shah, B.S. Nesbitt and D.S.F. Crothers, Studies of two-centre effects in double differential scattering of electrons using the CDW-EIS model, The Sixth European Conference on Atomic and Molecular Physics, Siena, 14–18 July (1998).Google Scholar

Copyright information

© Springer Science+Business Media New York 1999

Authors and Affiliations

  • S. F. C. O’Rourke
    • 1
  • W. Schmitt
    • 2
  • R. Moshammer
    • 3
  • J. Ullrich
    • 3
  • B. S. Nesbitt
    • 1
  • D. S. F. Crothers
    • 1
  1. 1.Department of Applied Mathematics and Theoretical PhysicsThe Queen’s University of BelfastBelfastNorthern Ireland
  2. 2.Gesellschaft für SchwerionenforschungDarmstadtGermany
  3. 3.Universität FreiburgFreiburgGermany

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