Reactions of SO3 with the O/H radical pool under combustion conditions

The reactions of SO(3) with H, O, and OH radicals have been investigated by ab initio calculations. For the SO(3) + H reaction (1), the lowest energy pathway involves initial formation of HSO(3) and rearrangement to HOSO(2), followed by dissociation to OH + SO(2). The reaction is fast, with k(1) = 8.4 x 10(9)T(1.22) exp(-13.9 kJ mol(-1)/RT) cm(3) mol(-1) s(-1) (700-2000 K). The SO(3) + O -> SO(2) + O(2) reaction (2) may proceed on both the triplet and singlet surfaces, but due to a high barrier the reaction is predicted to be slow. The rate constant can be described as k(2) = 2.8 x 10(4)T(2.57) exp(-122.3 kJ mol(-1)/RT) cm(3) mol(-1) s(-1) for T > 1000 K. The SO(3) + OH reaction to form SO(2) + HO(2) (3) proceeds by direct abstraction but is comparatively slow, with k(3) = 4.8 x 10(4)T(2.46) exp(-114.1 kJ mol(- 1)/RT) cm(3) mol(-1) s(-1) (800-2000 K). The revised rate constants and detailed reaction mechanism are consistent with experimental data from batch reactors, flow reactors, and laminar flames on oxidation of SO(2) to SO(3). The SO(3) + O reaction is found to be insignificant during most conditions of interest; even in lean flames, SO(3) + H is the major consumption reaction for SO(3).