RESONANCES IN THE CH-2-]HCN+N(S-4) REACTION - THE DYNAMICS OF A SPIN-FORBIDDEN PROCESS(N)

The dynamics of the CH+N-2(X (1) Sigma(g)(+))-->HCN+N(S-4) reaction is studied theoretically for the first time. A simple two-dimensional mo del is developed, treating the reaction dynamics on the doubler and on the quarter Born-Oppenheimer surfaces of CHN2 by exact quantum mechan ics and the coupling between the two electronic states within first-or der perturbation theory. Summation over total angular momentum states is carried out within the J-shifting approximation and the Boltzmann r ate constant is computed over the temperature range of interest for co mbustion T less than or similar to 1700 K. The reaction probability ex hibits a rich resonance pattern, manifesting the existence of long-liv ed quasibound intermediate states on both the doubler and the quartet surfaces. These resonances affect the dynamics profoundly, being the d riving force behind the spin-changing reaction. The thermal rate const ant increases with temperature in an Arrhenius type fashion and in qua litative agreement with high-temperature experiments.