Revolutionary advances in experimental techniques and spectacular increases in computer power over recent years have enabled researchers to develop a much more profound understanding of the atomic few-body problem. One area of intense focus has been the study of fragmentation processes. Covering the latest research in the field, this edited text is the first to provide a focussed and systematic treatment of fragmentation processes, bringing together contributions from a range of leading experts. As well as tackling the more established electron-impact ionization processes, (e,2e), this book also guides the reader through topics such as molecular fragmentation, ion-atom collisions and multi-photon processes. Combining a broad range of topics with an equal mix of theoretical and experimental discussion, this is an invaluable text for graduate students and researchers in atomic collisions, laser physics and chemistry.

In the past few years, revolutionary advances in experimental techniques and spec-tacular increases in computer power have offered unique opportunities to develop a much more profound understanding of the atomic few-body problem. One area of intense effort is the study of fragmentation processes - break-up processes - which are studied experimentally by detecting in coincidence the collisional frag-ments with their angles and energies resolved. These experiments offer a unique insight into the delicacies of atomic and molecular interactions, being at the limit of what is quantum mechanically knowable; the fine detail that is revealed would be swamped in a less differential measurement. The challenge for the theorist is to develop mathematical and computational techniques which are of sufficient inge-nuity and sophistication that they can elucidate the Physics observed in existing measurements and give direction to the next generation of experiments. Fragmen-tation processes are studied by those interested in electron and photon impact ionization, heavy particle collisions, collisions involving antimatter, as well as molecular collisions.
Colm T. Whelan
31 January 2012

List of contributors page ix

Preface xi

1 Direct and resonant double photoionization: from atoms to solids 1

1.1 Introduction

1.2 Direct double photoionization 3

1.3 Indirect double photoionization 21

1.4 Conclusions 40

2 The application of propagating exterior complex scaling to atomic collisions 48

2.1 Introduction 48

2.2 Introduction to exterior complex scaling 49

2.3 Application of ECS to electron-hydrogen scattering 53

2.4 Scattering in electron-hydrogen system 58

2.5 Exterior complex scaling for electron-helium scattering 61

2.6 Summary and outlook for the future 69

3 Fragmentation of molecular-ion beams in intense ultrashort laser pulses 72

3.1 Introduction 72

3.2 Experimental method 75

3.3 Benchmark molecules 82

3.4 Complex and/or unique molecular ions 87

3.5 Summary and outlook 94

4 Atoms with one and two active electrons in strong laser fields 98

4.1 Introduction 98

4.2 Theoretical model 99

4.3 Two-photon double ionization of helium 101

4.4 DC-assisted double photoionization of He and H- 103

4.5 Strong-field ionization of lithium and hydrogen 105

4.6 High harmonics generation 108

4.7 Time delay in atomic photoionization 110

5 Experimental aspects of ionization studies by positron and positronium impact 116

5.1 Introduction 116

5.2 Integral cross sections for positron impact ionization 117

5.3 1 Differential cross sections for positron impact ionization 122

5.4 Positronium-induced fragmentation 129

5.5 Conclusions and outlook 133

6 (e,2e) spectroscopy using fragmentation processes 137

6.1 Introduction 137

6.2 Background 139

6.3 Theory 142

6.4 Electron momentum spectroscopy results 143

6.5 Low-energy (e,2e) results 147

6.6 Conclusion 152

7 A coupled pseudostate approach to the calculation of ion-atom fragmentation processes 155

7.1 Introduction 155

7.2 Theory 155

7.3 Antiproton-induced ionization 160

8 Electron impact ionization using (e,2e) coincidence techniques from threshold to intermediate energies 164

8.1 Introduction 164

8.2 Experimental methods and techniques 171

8.3 Theoretical models 181

8.4 Atomic targets 186

8.5 Molecular targets 196

8.6 Experiments from laser-aligned atoms 200

8.7 Future work and conclusions 203

9 (e,2e) processes on atomic inner shells 207

9.1 (e,2e) processes - an overview 207

9.2 Non-relativistic theory 208

9.3 The distorted wave Born approximation 212

9.4 Inner-shell ionization of heavy metal targets at relativistic impact energies 221

9.5 General features of the cross section 228

9.6 Special features 230

10 Spin-resolved atomic (e,2e) processes 243

10.1 Introduction 243

10.2 Experimental considerations 245

10.3 Low-Z targets and low electron impact energies 247

10.4 High-Z targets and low electron impact energies 249

10.5 High-Z targets and high electron impact energies 254

10.6 Longitudinally polarized electrons 260

10.7 Conclusion 265

Index 268

Colm T. Whelan is a Professor in the Department of Physics, Old Dominion University, Norfolk, Virginia, USA. He received his Ph.D. in Theoretical Atomic Physics from the University of Cambridge in 1985 and was elected an Eminent Scholar at Old Dominion University in 2003. He is a fellow of the American Physical Society and the Institute of Physics (UK). He has edited five previous books and has written over 150 research papers, mostly on atomic collision physics.

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