PARAMETERIZATION OF PRESSURE-DEPENDENT AND TEMPERATURE-DEPENDENT KINETICS IN MULTIPLE WELL REACTIONS

It is now well confirmed that the influence of temperature on the fall -off behavior of dissociation recombination and chemically-activated r eactions can be dramatic. For single-well, single-product dissociation reactions, it is customary to approximate these fall-off surfaces usi ng extensions of Lindemann's empirical expression. We consider here ch emical-activation and dissociation reactions possessing multiple wells and multiple products. We show that direct approximation of the rate coefficients via Chebyshev expansions yields reliable and accurate rep resentations of their pressure and temperature dependences, which are superior to those from a Lindemann approach to fit the form factor rep resenting the fall-off surface. The superiority of the method is demon strated in a study of seven channels corresponding to four different r eactions important in combustion chemistry over the ranges 300-3,000 K and 0.02-200 atm.