This three-year award supports U.S.-France cooperative research in physical chemistry between Eric A. Gislason of the University of Chicago and Muriel Sizun and P.M. Guyon of the University of Paris, Orsay. The investigators propose to continue experimental and theoretical studies of ion-molecule collisions. They will examine the charge transfer of diatomic ions, extend their earlier work on helium and hydrogen collisions, and develop a new, sequential model for energy transfer in atom-diatom collisions. Dr. Gislason brings to this project extensive experience in theoretical and experimental research of ion-molecule collisions. His current research deals with the theory of molecular vibration in transition phases. This is complemented by the French investigators expertise in experimental aspects of ion-molecule collisions. The project will benefit from access to the synchrotron facility at the University of Paris, Orsay, one of the world's centers for ion-molecule collision studies. And their combined efforts will advance our understanding of the behavior of molecules in the aggregate and the importance of ion-molecule collisions in low pressure processing plasmas.