This volume contains the invited papers and selected contributed papers presented at the International Symposium on 'Electron-Molecule Scattering and Photoionization' held at SERC's Daresbury Laboratory, Cheshire, England from 18th to 19th July, 1987. This Symposium was a Satellite Meeting to the XVth International Conference on the Physics of Electronic and Atomic Collisions (ICPEAC I and follows a tradition of Satellite Meetings i. n related areas of collisions held in association with previous ICPEAC's. In order to make this volume as representative of the Symposium as possible 'Hot Topics' presented orally at the meeting together with a few papers selected by the Programme Committee from the contributed posters are included. The Editors are grateful to the authors for responding rapidly to the invitation to submit their contri butions for inclusion in the volume, as indeed they are grateful to all the authors for the high quality of their contributions. The Symposium brought together over 100 scientists from many countries and from broad interdisciplinary backgrounds to hear about current rapid advances in electron-molecule scatteri. ng and photoioniza tion. These advances have been stimulated on the experimental side by the increasing availability of electron beams with millivolt energy resolution, by synchrotron radiation sources and by intense tunable lasers. On the theoretical side the introduction of new computational methods enables accurate predictions to be made, resulting in a new and deeper understanding of the basic physical processes involved.

The collision of electrons with molecules and molecular ions is a fundamental pro cess in atomic and molecular physics and in chemistry. At high incident electron en ergies, electron-molecule collisions are used to deduce molecular geometries, oscillator strengths for optically allowed transitions, and in the case of electron-impact ionization, to probe the momentum distribution of the molecule itself. When the incident electron energy is comparable to or below those of the molecular valence electrons, the physics involved is particularly rich. Correlation and exchange effects necessary to describe such collision processes bear a close resemblance to similar efft:cts in the theory of electronic structure in molecules. Compound state formations, in the form of resonances and vir tual states, manifest themselves in experimental observables which provide details of the electron-molecule interactions. Ro-vibrational excitations by low-energy electron collisions exemplify energy transfer between the electronic and nuclear motion. The role of nonadiabatic interaction is raised here. When the final vibrational state is in the continuum, molecular dissociation occurs. Dissociative recombination and dissociative attachment are examples of such fragmentation processes. In addition to its fundamental nature, the study of electron-molecule collisions is also motivated by its relation to other fields of study and by its technological appli cations. The study of planetary atmospheres and the interstellar medium necessarily involve collision processes of electrons with molecules and molecular ions.

Scattering phenomena play an important role in modern physics. Many significant discoveries have been made through collision experiments. Amongst diverse kinds of collision systems, this book sheds light on the collision of an electron with a molecule. The electron-molecule collision provides a basic scattering problem. It is scattering by a nonspherical, multicentered composite particle with its centers having degrees of freedom of motion. The molecule can even disintegrate, Le., dissociate or ionize into fragments, some or all of which may also be molecules. Although it is a difficult problem, the recent theoretical, experimental, and computational progress has been so significant as to warrant publication of a book that specializes in this field. The progress owes partly to technical develop ments in measurements and computations. No less important has been the great and continuing stimulus from such fields of application as astrophysics, the physics of the earth's upper atmosphere, laser physics, radiation physics, the physics of gas discharges, magnetohydrodynamic power generation, and so on. This book aims at introducing the reader to the problem of electron molecule collisions, elucidating the physics behind the phenomena, and review ing, to some extent, up-to-date important results. This book should be appropri ate for graduate reading in physics and chemistry. We also believe that investi gators in atomic and molecular physics will benefit much from this book.

There has been a steady advance of the atomic and molecular many-body methodology over the last few years, with a concomitant development of versatile computer codes. Understanding and interpretation of electronic structural features and the associated spectroscopic properties via many-body techniques are becoming competitive with those obtained with the traditional formalisms. Since the many-body techniques are not yet a part of the repertoire of the "black-box tools" of electronic structure and spectroscopy, it seems worthwhile to take stock now of the recent progress in certain selected areas. The present volume is more in the nature of proceedings of a "Paper Symposium," rather than of one which actually took place. We did organize in Calcutta, between December 10 and 12, 1990, a small meeting on Applied Many-Body Methods to Spectroscopy and Electronic Structure, jointly organized by the Indian Association for the Cultivation of Science and the S.N. Bose National Centre for Basic Sciences. Several leading practitioners were invited, among which some could not come for various reasons.

The First Asilomar Conference on Electron- and Photon-Molecule Collisions was held August 1-4, 1978 in Pacific Grove, California. This meeting brought together forty scientists who are actively involved in theoretical studies of electron scattering by, and photoionization of, small molecules. In this volume, are collected the contributions of the invited speakers, as well as the roundtable and evening discussions condensed from taped recordings of the entire proceedings. The subject matter reflects current activity in the field and describes many of the techniques that are being developed and applied to molecular collision problems. We would like to thank the Air Force Office of Scientific Research (AFOSR) and the Office of Naval Research (ONR) for providing the financial support that made this conference possible. Special thanks are due to Dr. Robert Junker of ONR and Dr. Ralph Kelley of AFOSR for the interest and encouragement they provided in all phases of this meeting. We also thank all the participants whose efforts and contributions made this conference a success. Finally, we thank Ms. Charlotte MacNaughton and Ms. Sara Jackson for the many hours they spent transcribing tapes and preparing this volume for publication.