Table Of ContentSpringer Series on 20
Atorns+Pias. ..a s
Guest Editor: Prof. J. P. Toennies
Springer-Verlag Berlin Heidelberg GmbH
Springer Series on
Atotns+PiasDJas
Editors: G. Ecker P. Lambropoulos I. I. Sobel'man H. Walther
Managing Editor: H. K. V. Lotsch
Polarized Electrons 2nd Edition 12 Atomic Spectra
By J. Kessler and Radiative Transitions 2nd Edition
By I. I. Sobel' man
2 Multiphoton Processes
13 Multiphoton Processes in Atoms
Editors: P. Lambropoulos and S. J. Smith
By N. B. Delone and V. P. Krainov
3 Atomic Many-Body Theory
14 Atoms in Plasmas
2nd Edition
By V. S. Lisitsa
By I. Lindgren and J. Morrison
15 Excitation of Atoms
4 Elementary Processes
and Broadening of Spectral Lines
in Hydrogen-Helium Plasmas
2nd Edition
Cross Sections
By I. I. Sobel'man, L. Vainshtein,
and Reaction Rate Coefficients
By R. K. Janev, W. D. Langer, K. Evans, Jr., and E. Yukov
and D. E. Post, Jr. 16 Reference Data
on Multicharged Ions
5 Pulsed Electrical Discharge
By V. G. Pal'chikov and V. P. Sheve1ko
in Vacuum
By G. A. Mesyats and D. I. Proskurovsky 17 Lectures on Non-linear Plasma
Kinetics
6 Atomic and Molecular Spectroscopy
By V. N. Tsytovich
2nd Edition
Basic Aspects and Practical Applications 18 Atoms and Their
By S. Svanberg Spectroscopic Properties
By V. P. Shevelko
7 Interference of Atomic States
By E. B. Alexandrov, M.P. Chaika 19 X-Ray Radiation
and G. I. Khvostenko of Highly Charged Ions
By H. F. Beyer, H.-J. Kluge,
8 Plasma Physics 2nd Edition
and V. P. Shevelko
Basic Theory
with Fusion Applications 20 Electron Emission
By K. Nishikawa and M. Wakatani in Heavy Ion-Atom Collision
By N. Stolterfoht, R. D. DuBois,
9 Plasma Spectroscopy
and R. D. Rivarola
The Influence of Microwave
and Laser Fields 21 Molecules and Their
ByE. Oks Spectroscopic Properties
By S. V. Khristenko, A. I. Mas1ov,
10 Film Deposition
and V. P. Sheve1ko
by Plasma Techniques
ByM. Konuma
11 Resonance Phenomena
in Electron-Atom Collisions
By V.I. Lengyel, V. T. Navrotsky
and E. P. Sabad
N. Stolterfoht R. D. DuBois
R.D. Rivarola
Electron Emission
in Heavy Ion-Atom
Collisions
With 78 Figures
~Springer
Priv.-Doz. Dr. Nikolaus Stolterfoht Professor Robert D. DuBois
Hahn-Meitner-Institut Berlin, University of Missouri-Rolla,
GlienickerstraBe 100 Oepartment of Physics
0-14109 Berlin, Germany Rolla, MO 65401, USA
Professor Roberto D. Rivarola
Universidad Nacional de Rosario,
and Instituto de Fisica Rosario, CONICET,
Rosario, 2000, Argentina
Guest Editor: Professor Dr. J. Peter Toennies
Max-Planck-Institut fiir Striimungsforschung, Bunsenstrasse !O,
0-37073 Giittingen, Germany
Series Editors:
Professor Dr. Giinter Ecker
Ruhr-Universităt Bochum, Lehrstuhl Theoretische Physik 1, Universitătsstrasse 150,
0-44801 Bochum, Germany
Professor Peter Lambropoulos, Ph. D.
Max-Planck-Institut fiir Quantenoptik, 0-85748 Garching, Germany, and
Foundation for Research and Technology - Hellas (FO.R.T.H.),
Institute of Electronic Structure & Laser (IESL) and
University ofCrete, PO Box 1527, Heraklion, Crete 71110, Greece
Professor Igor 1. Sobel'man
Lebedev Physics Institute, Russian Academy of Sciences,
Leninsky Prospekt 53, 117924 Moscow, Russia
Professor Dr. Herbert Walther
Sektion Physik der Universităt Miinchen, Am Coulombwall 1,
0-85748 Garching/Miinchen, Germany
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Die Deutsche Bibliothek - CIP-Einheitsaufnahme
Stolterfoht, Nikolaus: Electron emission in heavy ion-atom collision I N. Stolterfoht; R. D. DuBois; R. D. Rivarola.
(Springer series on atoms + plasmas; 20)
ISBN 978-3-642-08322-8 ISBN 978-3-662-03480-4 (eBook)
DOI 10.1007/978-3-662-03480-4
ISSN 0177 -6495
ISBN 978-3-642-08322-8
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SPIN 10632964 54/3144 -5 4 3 210 -Printed on acid-free paper
To
Gene Rudd
Preface
This book is devoted to 30 years of lively research that has taken place in
the field of ionization in ion-atom collisions. The ionization process, where
an electron is liberated to the continuum of an atom, is of vital interest for
basic research and many applications such as plasma physics, astrophysics,
and radiation physics. The book is a broad review of theoretical and experi
mental studies addressing electron emission in energetic ion-atom collisions.
High incident energies are considered, where the projectile velocity is greater
than the initial velocity of the electron participating in the emission process.
At high energies the projectile interactions may be considered as a relatively
weak perturbation. However, with the advent of highly charged projectile
ions, strong interactions can occur in energetic ion-atom collisions. The book
puts emphasis on the interpretation of different ionization mechanisms to
support a detailed understanding of processes leading to electron emission.
Hence, it is written for researchers interested in applications and students
learning fundamental aspects of ion-atom collisions. It addresses both exper
imentalists searching for information about the experimental apparatus and
theorists who want to enter into the field of collision physics. It is assumed
that readers interested in the theoretical methods are familiar with the basics
of quantum mechanics.
The review treats collisions involving incident bare ions as well as projec
tiles carrying electrons. The ionization mechanisms are classified in terms of
the strength of the electronic interaction with heavy particles. These mech
anisms are interpreted in terms of Coulomb centers formed by the positive
charges of the projectile and target nuclei, which interacts strongly with the
outgoing electron. In particular, the cases of electron emission in one and
two centers are analyzed. As examples, electron emission in binary and soft
collisions with bare projectiles are treated as cases for single-projectile and
target centers, respectively. General properties of two-center electron emis
sion are analyzed by using electron capture to the continuum and saddle-point
electron emission as specific examples. For dressed projectiles, particular at
tention is devoted to screening effects, anomalies in the binary-encounter
peak production, diffraction effects, and dielectronic processes involving two
active electrons. Lastly, a brief overview of multiple ionization processes is
presented. The survey concludes with a compilation of experimental studies
VIII Preface
related to heavy ion impact ionization. Publications that appeared before the
end of 1996 are taken into consideration.
This work has been prepared in close communication with many col
leagues who are too numerous to acknowledge individually. Their assis
tance and comments contributed greatly to this work. Our deepest thanks
go to Eugene Rudd whose research formed the foundation for this field
of study and whose ideas guided us at various stages of this review. We
are much indebted to Wolfgang Meckbach, Antoine Salin, Theo Zouros,
Bela Sulik, Mitio Inokuti, Victor Ponce, Gregor Schiwietz, John Tanis, and
Carlos Garibotti who critically read parts of the manuscript and provided
very valuable comments. We thank Laszlo Gulyas for his assistance in us
ing the CDW-EIS code. Numerous discussions and communications with
Carlos Reinhold, Joe Macek, Dave Schulz, Joachim Burgdorfer, Yasu Ya
mazaki, Pablo Fainstein, Knud Taulbjerg, Jorge Miraglia, and Ron Olson
are gratefully acknowledged. R. D. Rivarola acknowledges Silvia Corchs for
her valuable assistance in preparing part of the manuscript. R. D. Dubois is
indebted to the Hahn-Meitner Institute for support during his stay in Berlin.
N. Stolterfoht is greateful for support by the Instituto de Fisica during his
visit to the Universidad Nacional de Rosario.
Berlin, Rolla, Rosario N. Stolterfoht
August 1997 R. D. DuBois
R. D. Rivarola
Contents
1. Introduction.............................................. 1
2. Overview of Ionization Mechanisms....................... 5
2.1 Considerations to the Center Picture. . . . . . . . . . . . . . . . . . . . . . 6
2.2 Two Bodies: Binary-Encounter Electron Emission . . . . . . . . . . 8
2.3 Three Bodies: Single-Center Electron Emission . . . . . . . . . . . . . 11
2.4 Three Bodies: Two-Center Electron Emission . . . . . . . . . . . . . . 12
2.5 Four Bodies: Collisions Involving Projectile Electrons . . . . . . . 13
3. Theoretical Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
3.1 Two-Body Approximations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
3.1.1 The Rutherford Formula . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.1.2 Elastic Scattering Model . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.1.3 Binary Encounter Approximation . . . . . . . . . . . . . . . . . . 23
3.2 Classical Trajectory Monte Carlo Method . . . . . . . . . . . . . . . . . 25
3.3 Semiclassical Approximation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
3.3.1 Basic Formalisms................................. 31
3.3.2 Partial Wave Expansion........................... 32
3.3.3 Dipole Approximation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
3.3.4 Free Electron Peaking Approximation. . . . . . . . . . . . . . . 35
3.4 Born Approximations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
3.4.1 Free-Electron Approximation . . . . . . . . . . . . . . . . . . . . . . 37
3.4.2 First-Order Born Approximation . . . . . . . . . . . . . . . . . . . 40
3.4.3 Oppenheimer-Brinkman-Kramers Approximation..... 44
3.5 Distorted Wave Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
3.5.1 Continuum Distorted Wave Approximation . . . . . . . . . . 47
3.5.2 Continuum Distorted Wave-Eikonal
Initial State Approximation. . . . . . . . . . . . . . . . . . . . . . . . 49
3.5.3 Quantum-Mechanical Impulse Approximation . . . . . . . . 53
3.5.4 Distorted Strong Potential Born Approximation
and Related Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
3.6 Close-Coupling Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
X Contents
3. 7 Dressed Projectiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
3.7.1 First-Order Theory by Bates and Griffing . . . . . . . . . . . 66
3. 7.2 Higher-Order Theories for Binary Encounter Electrons 68
4. Experimental Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
4.1 Experimental Set-Up.................................... 75
4.2 Target Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
4.3 Electron Energy Analysis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
4.3.1 Low-Energy Electron Emission..................... 81
4.3.2 Background Suppression at Low Energies . . . . . . . . . . . . 82
4.3.3 High-Energy Electrons . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
4.4 Coincidence Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
4.4.1 Electron-Projectile Ion Coincidences . . . . . . . . . . . . . . . . 87
4.4.2 Electron-Target Ion Coincidences . . . . . . . . . . . . . . . . . . . 89
4.4.3 Outer Shell-Inner Shell Coincidences. . . . . . . . . . . . . . . . 92
5. Ionization by Bare Projectiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
5.1 Binary Encounter Collisions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
5.1.1 Shape of the Binary Encounter Peak................ 97
5.1.2 Shift of the Binary Encounter Peak ................. 102
5.2 Target-Center Phenomena ............................... 105
5.2.1 Early Observations ............................... 105
5.2.2 Energy Distribution of Soft-collision Electrons ....... 106
5.2.3 Angular Distribution of Soft Collision Electrons ...... 109
5.2.4 Backscattering of High-Energy Electrons
by the Target . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
5.3 Two-Center Phenomena ................................. 121
5.3.1 Electron Capture to the Continuum ................ 122
5.3.2 Two-Center Electron Emission ..................... 129
5.3.3 Saddle Point Electron Emission .................... 136
5.4 Saturation Effects ...................................... 141
5.4.1 Differential Cross Sections ......................... 142
5.4.2 Total Cross Sections .............................. 144
6. Ionization by Dressed Projectiles ......................... 149
6.1 Definitions and Notations ................................ 149
6.2 Screening Effects of Projectile Electrons ................... 150
6.2.1 Screened Point Charge ............................ 150
6.2.2 Experimental Studies ............................. 151
6.2.3 Theoretical Interpretation ......................... 154
6.3 Binary Encounter Electron Emission ...................... 160
6.3.1 Enhancement of the Binary Encounter Peak ......... 160
6.3.2 Diffraction Effects ................................ 165
