Fundamental Processes In Energetic Atomic Collisions

In recent years, the impact of new experimental techniques (e.g., nuclear physics methods, availability of high-intensity light sources) as well as an increasing demand for atomic collision data in other fields of physics (e.g., plasma physics, astrophysics, laser physics, surface physics, etc.) have stimulated a renewed, strong interest in atomic collision research. Due to the explosive development of the various fields, scientists often even have dif ficulty in keeping up with their own area of research; as a result, the overlap between different fields tends to remain rather limited. Instead of having access to the full knowledge accumulated in other fields, one uses only the small fraction which at the moment seems to be of immediate importance to one's own area of interest. Clearly, many fruitful and stimulating ideas are lost in this way, causing progress to be made much more slowly than it could be. Atomic col lision physics is no exception to this rule. Although it is of basic interest to many other areas, it is mostly regarded merely as a (nonetheless important) tool by which to gain additional information.

The Proceedings of the Advanced study Institute on Fundamental Processes in Atomic Collision Physics (Santa Flavia, Italy, September 10-21, 1984) are dedicated to the memory of Sir Harrie r-1assey, whose scientific achievements and life are reviewed herein by Sir David Bates. At the first School on the above topic (Maratea, September 1983, Volume 103 in this series), Harrie Massey presented the introductory lectures, summarized the entire lecture program, and presented an outlook on future developments in atomic collision physics. In an after-dinner speech, Massey recalled personal reminiscences and historical events with regard to atomic collision physics, to which he had contributed by initiating pioneering work and by stimulating and surveying this branch of physics over a period of almost six decades. Participants in the Maratea School will always remember Harrie Massey as a charming and wonderful person who was most pleased to discuss with everyone--students, postdoctorals, and senior scientists--any topic in atomic collision physics. Harrie Massey was a member of the Scientific Advisory Committee of the 1984 Santa Flavia School. Before his death he expressed his interest in attending this second School devoted to the presentation of recent developments and highlights in atomic collision physics. It is the desire of all authors to honor Harrie Massey with their contributions in these Proceedings.

The broad field of molecular collisions is one of considerable current interest, one in which there is a great deal of research activity, both experi mental and theoretical. This is probably because elastic, inelastic, and reactive intermolecular collisions are of central importance in many of the fundamental processes of chemistry and physics. One small area of this field, namely atom-molecule collisions, is now beginning to be "understood" from first principles. Although the more general subject of the collisions of polyatomic molecules is of great im portance and intrinsic interest, it is still too complex from the viewpoint of theoretical understanding. However, for atoms and simple molecules the essential theory is well developed, and computational methods are sufficiently advanced that calculations can now be favorably compared with experimental results. This "coming together" of the subject (and, incidentally, of physicists and chemists !), though still in an early stage, signals that the time is ripe for an appraisal and review of the theoretical basis of atom-molecule collisions. It is especially important for the experimentalist in the field to have a working knowledge of the theory and computational methods required to describe the experimentally observable behavior of the system. By now many of the alternative theoretical approaches and computational procedures have been tested and intercompared. More-or-Iess optimal methods for dealing with each aspect are emerging. In many cases working equations, even schematic algorithms, have been developed, with assumptions and caveats delineated.

This volume contains the lectures presented at the NATO Advanced study Institute "Fundamental Processes of Atomic Dynamics" held in Maratea. Italy from September 20th to October 2nd 1987. The institute and this volume were conceived as a natural complement to previous institutes held in Maratea (1982) and in Santa Flavia (1984. ) whose proceedings are to be found in NATO ASI Series B vol. 103 and 134 respectively. The subject matter of these institutes was the study of the funda mental processes occurring in the interactions of atoms with photons. electrons and heavy-ions. The aim has been to unify these processes in a coherent experimen tal and theoretical approach. The present volume brings this approach up to date and contains in addition. for contrast and variety. a description of similar dynamical processes in the study of clusters and surfaces. The institute was opened with a lecture by Joe Macek in which he summarised the current status of atomic collision research. propounded the philosophy of a unified approach to structure, fragmentation and collision and posed the outstanding questions in the field. This lecture forms the introduction to this volume. The subject matter was divided into experiment and theory with the lectures inter-linked so that the one could re-inforce the other. The whole of the theoretical part of the institute was organised by Ugo Fano as an on-going symposium.

The book is a comprehensive edition which considers the interactions of atoms, ions and molecules with charged particles, photons and laser fields and reflects the present understanding of atomic processes such as electron capture, target and projectile ionisation, photoabsorption and others occurring in most of laboratory and astrophysical plasma sources including many-photon and many-electron processes. The material consists of selected papers written by leading scientists in various fields.

The Hans Kleinpoppen Symposium on "Complete Scattering Experiments" th was held in honor of Hans Kleinpoppen’s 70 birthday. It took place in Il Ciocco, Italy. The symposium had two purposes: to present the work that Hans Kleinpoppen has done or initiated during his remarkable scientific career, and to bring people from various fields together who perform complete scattering experiments. Hans Kleinpoppen’s work included electron and photon impact experiments which were accompanied by studies of entangled states - a field of high current interest. Representatives from each of these fields gave excellent lectures on their particular subjects, and many discussions that started during the sessions were continued later in the relaxed atmosphere of the Il Ciocco resort. The breathtaking view of the beautiful landscape will be an unforg- table memory to all who participated in this extraordinary scientific event. The coherent and ideal combination of subject, people and location reflected the coherence of Hans Kleinpoppen’s aims and activities in science and life. We offer our grateful thanks to all contributers who made this volume such a worthy tribute to Hans Kleinpoppen. We also like to thank Rainer Hentges for the painstaking work to prepare this volume in its complete ready to print version. We are also grateful to the Royal Society of London and the Max– Planck–Gesellschaft who generous support of the Hans Kleinpoppen sym- sium made this marvelous meeting and this proceedings possible.

During the last two decades the experimental investigation of atomic coherence phenomena has made rapid progress. Detailed studies have been performed of angular correlations, spin polarization effects, angular momen tum transfer, and the alignment parameters which characterize the charge cloud of excited atoms. The enormous growth in the number of these investigations was made possible through substantial development and application of new experimental technology, the development of sophisti cated theoretical models and numerical methods, and a fine interplay between theory and experiment. This interplay has resulted in a deeper understanding of the physical mechanisms of atomic collision processes. It is the purpose of the chapters in this book to provide introductions for nonspecialists to the various fields of this area as well as to present new experimental and theoretical results and ideas. The interest in spin-dependent interactions in electron-atom scattering has a long history; it dates back to the early investigations of Mott in 1929. While the more traditional measurements in this field were concerned with the determination of spin polarization and asymmetries, the range of investi gations has been expanded enormously during the last few years and now includes many observables sensitive to one or more of the various spin dependent interactions. The understanding of these effects requires a theoretical description of the orientation and alignment parameters of the target atoms, of the forma tion of resonances, of the influence of electron-exchange processes, and of the relativistic interactions inside the atom and between projectile and target.