Sir David Bates celebrated his seventieth birthday on the 18th November 1986. To mark this event a conference was held in the David Bates building at The Queen's University of Belfast on the 17th and 18th November 1986. At this conference ex-students and colleagues of Sir David, who are acknowledged world experts in their field of research, gave in depth reviews of a particular area of atomic and molecular physics. This book on the conference presents a unique account of recent studies in atomic and molecular processes in a wide range of research fields. This volume is dedicated to Sir David by his friends as a token of their affection and respect. It is hoped that it will provide a useful summary of current research in atomic and molecular physics and that it will also show the great contribution which Sir David made to atomic and molecular physics. This conference was supported by the USAF European Office of Aerospace Research and Development who we wish to thank for their generous support. Arthur E. Kingston v CONTENTS Interstellar Cloud Chemistry Revisited 1 D.R. Bates Photo-ionisation of Atomic Oxygen . . . . . . . . . • • . • • • 29 M.J. Seaton The Formation of Complex Interstellar Molecules • • • • • . . .