Laboratoire de Chimie Structurale (UA 474), IURS Université de Pau, Avenue de l'Université, 64000 Pau, France
Abstract:
Saddle point geometries and barrier heights have been calculated for the H abstraction reaction HO2(2A″)+H(2S) → H2(1Σ+g)+O2(3Σ?g) and the concerted H approach-O removing reaction HO2 (2A″)+H(2S) → H2O(1A1)+O(3P) by using SDCI wavefunctions with a valence double-zeta plus polarization basis set. The saddle points are found to be of Cs symmetry and the barrier heights are respectively 5.3 and 19.8 kcal by including size consistent correction. Moreoever kinetic parameters have been evaluated within the framework of the TST theory. So activation energies and the rate constants are estimated to be respectively 2.3 kcal and 0.4×109 ? mol?1 s?1 for the first reaction, 20.0 kcal and 5.4.10?5 ? mol?1 s?1 for the second. Comparison of these results with experimental determinations shows that hydrogen abstraction on HO2 is an efficient mechanism for the formation of H2 + O2, while the concerted mechanism envisaged for the formation of H2O + O is highly unlikely.