Forward and reverse rate coefficients in equilibrating isomerization reactions

Abstract

Three models for the relaxation kinetics of a reversible unimolecular isomerization reaction are formulated and analyzed: a generalization of the simple Lindemann–Hinshelwood scheme, a detailed model with the strong collision approximation, and a master equation solution. For such systems the use of a classical relaxation analysis has been questioned. In each case it is found that the relaxation analysis does not give forward and reverse rate constants appropriate to the pure irreversible reactions, but that the rate constants so obtained can be interpreted in terms of irreversible schemes which allow for back reaction before collisional stabilization. The accuracy of this decomposition is linked with the applicability of the steady-state approximation for the populations of the reactive states, as is demonstrated analytically under the strong collision approximation, and numerically with the full master equation. An alternative approach using perturbation theory is shown to be unacceptably inaccurate.