This award will support collaborative research in physical chemistry between Dr. Daniel Kivelson, University of California at Los Angeles and Dr. Gilles Tarjus, University of Pierre and Marie Curie, Paris, France. The objective of the project is to develop a microscopic description of friction in liquids. The investigators are studying the motions of molecules in liquids, with particular emphasis on the motion of a reacting group traversing an activation barrier during a chemical reaction. In liquids the surrounding fluid plays an important role, not only in altering the activation energy, but also as a source of friction in determining all molecular motions. The project will focus on this frictional effect. Since friction is a macroscopic concept, they will seek to understand under what conditions it can validly and usefully be applied in describing dynamics at the molecular level. They will also explore how the frictional concept, extended if needed, to give a better microscopic description, can yield insights into chemical kinetics in liquid solution. Their approach will be both theoretical and computational. The results of this research should contribute to the understanding of frictional effects in liquids, particularly those connected with chemical reactions. Understanding chemical kinetics on a molecular level is one of the most fundamental problems in chemistry. Dr. Kivelson has been a leader in the area of studying molecular motions in liquids, particularly rotational motions, for many years, and he will benefit from the complementary expertise of Dr. Tarjus in the proposed research.