PERTURBED EQUILIBRIA AND STATISTICAL ENERGY REDISTRIBUTION IN A GAS-PHASE S(N)2 REACTION

The relative translational energy of one set of reactants in the gas-p hase equilibrium between chloride ion and chloroacetonitriie Cl-35(-) + (ClCH2CN)-Cl-37 reversible arrow Cl-37(-) + (ClCH2CN)-Cl-35 is varie d without affecting the energy distribution of the other set. The stea dy-state ratio of ionic isotopes changes so that there is an increase in the concentration of energized reactants. The ratio provides a meas ure of the translational energy dependence of the rate constant for th e bimolecular nucleophilic substitution (S(N)2) reaction. The observed energy dependence is indistinguishable from that predicted by Rice-Ra msperger-Kassel-Marcus theory, suggesting that the increased translati onal energy redistributes statistically in the collision complex.