This project, in the Experimental Physical Chemistry Program of the Chemistry Division, is in the field of low temperature ion chemistry. Prof. M. Smith of the University of Arizona, will study the binary chemistry of ion-molecule reactions and the relaxation and energy transfer at ultra low temperatures produced in a supersonic jet expansion of the reactant gases. He will also conduct photoelectron spectroscopy for state selection of molecular ions and cluster initiated state-selected chemical reactions. Using Laval nozzle expansions of the component gases the experiments will be extended to temperatures above those obtained with free jet expansions but below those accessible with conventional techniques. %%% The chemistry of ion-molecule has been studied in many laboratories yet there are very few investigations in the regime of very low temperatures. Prof. Smith's research in this field has had notable successes and he is one of its very few practitioners. The results of this research will be important to astronomers modeling interstellar chemistry.