Hans Kleinpoppen - Böcker

The EPSRC (Engineering and Physical Science Research Committee of the U. K. ) suggested two Workshops (York University, 22-23 September, 1993 and 15-16 April, 1994) for possible development of polarized electron/photon physics as targeted areas of research. The remit of these meetings included identifying research groups and their activities in polarized electron/polarized photon physics, listing relevant existing facilities (particularly electron spin sources and polarimeters), possible joint projects between research groups in the U. K. , recognizing future needs of projects for research of the highest scientific merit and referring to international comparisons of these research activities. Although very diverse but interconnected, the areas of research presented at the Workshops embrace atomic, molecular, surface, and solid state physics. In more detail these areas covered: electron spin correlations and photon polarization correlations in atomic and molecular collisions and photoionization, electron spin effects in scanning tunneling microscopy, surface and interface magnetism from X-ray scattering and polarized Auger electrons (including analysis of domain structures in solids and surfaces), polarized electrons from multiphoton ionization, quasi-atomic effects in solid state physics, dichroism in molecular and surface processes, Faraday rotation and high-field magneto-optics and polarization effects in simultaneous higher order electron-photon excitations. It is obvious from the spectrum of research fields presented at the Workshops that physicists of primarily two communities, namely those studying electron and photon spin interactions with gaseous atomic and molecular targets and those using condensed matter targets for their studies, interacted very closely witheach other.

The content of this book describes in detail the results of the present measurements of the partial and total doubly differential cross sections for the multiple-ionization of rare gas atoms by electron impact. These measurements show, beside other trends, the role of Auger transitions in the production of multiply ionized atoms in the region where the incident electron energy is sufficient to produce inner shell ionization. Other processes like Coster-Kronig transitions and shake off also contribute towards increasing the charge of the ions. The incident electron having energy of 6 keV, for example, in a collision with xenon atom can remove up to nine electrons! (*) X-ray-ion coincidence spectroscopy of the electron xenon atom collisions is also described.  The present measurements of doubly differential cross sections for the dissociative and non-dissociative ionization of hydrogen, sulfur dioxide and sulfur hexa fluoride molecular gases by electron impact are also described in the text of this book. The results of the measurements for sulfur dioxide molecule show how this major atmospheric pollutant can be removed from the atmosphere by electron impact dissociation of this molecule. The present results of the measurements for sulfur hexa fluoride give an insight into the dissociation properties of this molecular gas, which is being so widely used as a gaseous insulator in the electrical circuits.   The book also describes the present measurements of the polarization parameters of the fluorescence radiation emitted by the electron-impact-excited atoms of sodium and potassium. In these investigations the target atoms are polarized, therefore, the measurements of the polarization parameters give information about the electron atom interaction in terms of the interference, direct and exchange interaction channels.

H. J. BEYER AND H. KLEINPOPPEN We are pleased to present Part D of Progress in Atomic Spectroscopy to the scientific community active in this field of research. When we invited authors to contribute articles to Part C to be dedicated to Wilhelm Hanle, we received a sufficiently enthusiastic response that we could embark on two further volumes and thus approach the initial goal (set when Parts A and B were in the planning stage) of an almost comprehensive survey of the current state of atomic spectroscopy. As mentioned in the introduction to Parts A and B, new experimental methods have enriched and advanced the field of atomic spectroscopy to such a degree that it serves not only as a source of atomic structure data but also as a test ground for fundamental atomic theories based upon the framework of quantum mechanics and quantum electrodynamics. However, modern laser and photon correlation techniques have also been applied successfully to probe beyond the "traditional" quantum mechanical and quantum electrodynamical theories into nuclear structure theories, electro­ weak theories, and the growing field of local realistic theories versus quan­ tum theories. It is obvious from the contents of this volume and by no means surprising that applications of laser radiation again played a decisive role in the development of new and high-precision spectroscopic techniques.

H. KLEINPOPPEN AND J. F. WILLIAMS It has only very recently become possible to study angular correlations and coherence effects in different areas of atomic collision processes: These investigations have provided us with an analysis of experimental data in terms of scattering amplitudes and their phases, of target parameters such as orientation, alignment, and state multipoles, and also of coherence parameters (e. g. , the degree of coherence of excita­ tion). In this way the analysis of electron-photon, ion-photon, atom-photon, or electron-ion coincidences from electron-atom, ion-atom, or atom-atom collisional excitation has led to a breakthrough such that the above quantities represent most crucial and sensitive tests for theories of atomic collision processes. Similarly, the powerful (e, 2e) experiments (electron-electron coincidences from impact ionization of atoms) have attracted much attention where improved experimental studies and detailed theoretical description provide a wealth of information on either the col­ lisional ionization process or the atomic structure of the target atom. Interference effects, many-electron correlations, and energy and angular momen­ tum exchange between electrons in a Coulomb field playa decisive role in the under­ standing of postcollision interactions. New results on coherence effects and orienta­ tion and alignment in collisional processes of ions with surfaces and crystal lattices show links to relevant interference phenomena in atomic collisions. In small-angle elastic electron-atom scattering the effect of angular coherence can be studied in a crossed beam experiment.

In the spring of 1970 Peter Farago organised a three-day conference on Polarised Electron Beams at Carberry Tower, near Edinburgh. Although the development of the gallium arsenide source, which was to revolutionise the world of experimental polarised electron physics, was still some years in the future, the meeting provided an important forum for the exchange of ideas among theoreticians and experimentalists engaged in both high and low energy electron collision studies. As soon as the decision had been taken to hold the 5th European Conference on Atomic and Molecular Physics in Edinburgh in 1995, it occurred to the editors of the present volume that it would be highly appropriate to mark the twenty-fifth anniversary of the Carberry Tower Conference by organising an ECAMP satellite meeting in honour of Peter Farago. The opportunity to pay tribute to Peter's many important contributions in the broad field of electron physics attracted colleagues from allover the world to the symposium, which was held in the rooms of the Royal Society of Edinburgh on 31st March and 1st April 1995. Peter himself, now Professor Emeritus at the University of Edinburgh, was present throughout the meeting. We were particularly happy to welcome back to Edinburgh many participants in the original Carberry Tower conference; these included Professor P. G. Burke, Professor J. Kessler, Professor E. Reichert and Professor H. C. Siegmann, whose review papers had been highlights of the 1970 meeting.

The content of this book describes in detail the results of the present measurements of the partial and total doubly differential cross sections for the multiple-ionization of rare gas atoms by electron impact. These measurements show, beside other trends, the role of Auger transitions in the production of multiply ionized atoms in the region where the incident electron energy is sufficient to produce inner shell ionization. Other processes like Coster-Kronig transitions and shake off also contribute towards increasing the charge of the ions. The incident electron having energy of 6 keV, for example, in a collision with xenon atom can remove up to nine electrons! (*) X-ray-ion coincidence spectroscopy of the electron xenon atom collisions is also described.  The present measurements of doubly differential cross sections for the dissociative and non-dissociative ionization of hydrogen, sulfur dioxide and sulfur hexa fluoride molecular gases by electron impact are also described in the text of this book. The results of the measurements for sulfur dioxide molecule show how this major atmospheric pollutant can be removed from the atmosphere by electron impact dissociation of this molecule. The present results of the measurements for sulfur hexa fluoride give an insight into the dissociation properties of this molecular gas, which is being so widely used as a gaseous insulator in the electrical circuits.   The book also describes the present measurements of the polarization parameters of the fluorescence radiation emitted by the electron-impact-excited atoms of sodium and potassium. In these investigations the target atoms are polarized, therefore, the measurements of the polarization parameters give information about the electron atom interaction in terms of the interference, direct and exchange interaction channels.

The EPSRC (Engineering and Physical Science Research Committee of the U. K. ) suggested two Workshops (York University, 22-23 September, 1993 and 15-16 April, 1994) for possible development of polarized electron/photon physics as targeted areas of research. The remit of these meetings included identifying research groups and their activities in polarized electron/polarized photon physics, listing relevant existing facilities (particularly electron spin sources and polarimeters), possible joint projects between research groups in the U. K. , recognizing future needs of projects for research of the highest scientific merit and referring to international comparisons of these research activities. Although very diverse but interconnected, the areas of research presented at the Workshops embrace atomic, molecular, surface, and solid state physics. In more detail these areas covered: electron spin correlations and photon polarization correlations in atomic and molecular collisions and photoionization, electron spin effects in scanning tunneling microscopy, surface and interface magnetism from X-ray scattering and polarized Auger electrons (including analysis of domain structures in solids and surfaces), polarized electrons from multiphoton ionization, quasi-atomic effects in solid state physics, dichroism in molecular and surface processes, Faraday rotation and high-field magneto-optics and polarization effects in simultaneous higher order electron-photon excitations. It is obvious from the spectrum of research fields presented at the Workshops that physicists of primarily two communities, namely those studying electron and photon spin interactions with gaseous atomic and molecular targets and those using condensed matter targets for their studies, interacted very closely witheach other.

The main goal of this book is to elucidate what kind of experiment must be performed in order to determine the full set of independent parameters which can be extracted and calculated from theory, where electrons, photons, atoms, ions, molecules, or molecular ions may serve as the interacting constituents of matter. The feasibility of such perfect' and-or `complete' experiments, providing the complete quantum mechanical knowledge of the process, is associated with the enormous potential of modern research techniques, both, in experiment and theory. It is even difficult to overestimate the role of theory in setting of the complete experiment, starting with the fact that an experiment can be complete only within a certain theoretical framework, and ending with the direct prescription of what, and in what conditions should be measured to make the experiment `complete'. The language of the related theory is the language of quantum mechanical amplitudes and their relative phases. This book captures the spirit of research in the direction of the complete experiment in atomic and molecular physics, considering some of the basic quantum processes: scattering, Auger decay and photo-ionization. It includes a description of the experimental methods used to realize, step by step, the complete experiment up to the level of the amplitudes and phases. The corresponding arsenal includes, beyond determining the total cross section, the observation of angle and spin resolved quantities, photon polarization and correlation parameters, measurements applying coincidence techniques, preparing initially polarized targets, and even more sophisticated methods. The `complete' experiment is, until today, hardly to perform. Therefore, much attention is paid to the results of state-of-the-art experiments providing detailed information on the process, and their comparison to the related theoretical approaches, just to mention relativistic multi-configurational Dirac-Fock,convergent close-coupling, Breit-Pauli R-matrix, or relativistic distorted wave approaches, as well as Green's operator methods. This book has been written in honor of Herbert Walther and his major contribution to the field but even to stimulate advanced Bachelor and Master students by demonstrating that obviously nowadays atomic and molecular scattering physics yields and gives a much exciting appreciation for further advancing the field.