Professor Robert Gordon, University of Illinois at Chicago, is supported by a grant from The Physical Chemistry Program to perform experimental tests of reaction rate theories. Dr. Gordon is making use of current state-of-the-art molecular beam techniques to study reactions between very simple molecules at the most fundamental level. The results gleaned from these experiments should provide valuable tests of prevailing theories of chemical reactions at the molecular level. Two extreme mass combinations will be studied in order to reveal unusual dynamic effects and to test theoretical predictions. In one case the transfer of a light atom (hydrogen) between two heavy partners (chlorine 35 and chlorine 37) will be studied, and in the other case the exchange of two light partners (hydrogen and deuterium) in hydrogen chloride will be investigated. Specific questions to be addressed include: the validity of the transition state theory for treating these reactions; the contribution of tunneling to the reaction rate; the structure in the energy dependence of the reaction cross section; the effects of the attractive and repulsive features of the potential energy surface.