Activation energy for thermal decomposition of nitric oxide

Variation of the reaction mechanism for homogeneous thermal decomposition of NO into N-2 and O-2 in the temperature range between 1000 and 4000 K is studied. The decomposition always proceeds through an atomic chain mechanism initiated by formation of oxygen atom. However the step of the oxygen atom initiation depends on the reaction condition, i.e., collision between two NO molecules at low conversions (when P-O2/P-NO ratio << 1) and collision between NO and O-2 and/or unimolecular decomposition of O-2 at high conversions (after substantial O-2 has been accumulated from the reaction). In this study, apparent activation energy (E(app)) of the decomposition reaction has been theoretically determined on the basis of our proposed mechanisms. The E(app) thus determined varies widely (from 254 to 401 kj mol(-1)) with the accepted step of initiation. This variation can account for the variations among experimental activation energies for the decomposition reaction in the literature. (C) 1996 John Wiley & Sons, Inc.