The reaction between ethyl and molecular oxygen II: Further analysis

Abstract

The present investigation is a rather substantial extension and elaboration of our previous work on the same reaction. In this article we accomplish four primary objectives: 1. We show quantitatively how sensitive the high-temperature rate coefficient k(T) is to E02, the threshold energy of the transition state for direct molecular elimination of HO2 from ethylperoxy radical (C2H5O2), thus deducing a value of E02=−3.0 kcal/mol (measured from reactants). 2. We derive the result that k0(T) ≈ k′∞(T) in the high-temperature regime, where k0(T) is the zero-pressure rate coefficient, and k′∞(T) is the infinite-pressure rate coefficient for the bimolecular channel. 3. Most importantly, we discuss the three different regimes of the reaction (low-temperature, transition, and high-temperature) in terms of the eigenvectors and eigenvalues of G, the transition matrix of the master equation. The transition regime is shown to be a region of avoided crossing between the two chemically significant eigenvalue curves in which the thermal rate coefficient k (T ,p) jumps from one eigenvalue to the other. This jump is accompanied by a “mixing” of the corresponding eigenvectors, through which both eigenvectors deplete the reactant. The onset of the high-temperature regime is triggered by reaching the “stabilization limit” of the ethylperoxy adduct, a limit that is induced by a shift in equilibrium of the stabilization reaction. Our identification of the prompt and secondary HO2 formed by the reaction with these eigenvalue/eigenvector pairs leads to good agreement between theory and the experiments of Clifford et al. (J Phys Chem A 2000, 104, 11549–11560). 4. Lastly, we describe the master equation results in terms of a set of elementary reactions and phenomenological rate coefficients. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 732–740, 2001