INTERNAL EXCITATION IN THE PRODUCTS OF NUCLEOPHILIC-SUBSTITUTION FROMTHE DISSOCIATION OF METASTABLE ION COMPLEXES

The relative kinetic energy distributions for the products of the diss ociation bf four metastable gas-phase ion clusters have been analyzed by means of ion kinetic energy spectroscopy;and the results modeled us ing statistical phase space theory. The systems studied represent reac tion intermediates in bimolecular nucleophilic substitutions (S(N)2). These studies build on previous investigations that; demonstrated vibr ational excitation in the products of the substitution reactions of ha lide ions with methyl halides.(1) The present studies explore the effe cts of molecular structure, reaction exothermicity, and nucleophile an d leaving group variation. The experimental kinetic energy distributio ns are compared with theoretical distributions calculated for statisti cal partitioning of energy among internal modes and relative kinetic e nergy of the products. In-each-reaction, the calculated distributions agree with the experimental distributions only if a significant fracti on of the energy released in the exothermic reactions:is assumed to be unavailable for randomization in the dissociation. The results sugges t-that the products of these S(N)2 reactions are internally excited.