Atmospheric chemistry of benzaldehyde: UV absorption spectrum and reaction kinetics and mechanisms of the C6H5C(O)O2 radical

Abstract

Flash photolysis–UV absorption and long pathlength FTIR–smog chamber studies of several reactions involving C6H5C(O) and C6H5C(O)O2 radicals have been performed. It was determined that reaction of Cl atoms with C6H5CHO proceeds via abstraction of the aldehydic hydrogen to give benzoyl radicals. The sole atmospheric fate of benzoyl radicals is addition of O2 to give peroxybenzoyl radicals. Reaction of C6H5C(O) radicals with molecular chlorine proceeds with a rate constant of (5.9±0.4)×10-11 cm3 molecule-1 s-1 at 296 K and 1–700 Torr total pressure. The UV spectrum of C6H5C(O)O2 radicals (245–300 nm) and the self reaction were investigated simultaneously, yielding σmax=(2.0±0.1)×10-17 cm2 molecule-1 at 245 nm and k16=(3.1±1.4)×10-13 exp[(1110±160) K/T] cm3 molecule-1 s-1, measured from 298 to 460 K. At 338 K, C6H5C(O)O2 radicals react with NO with a rate constant of (1.6±0.4)×10-11 cm3 molecule-1 s-1. At 296 K, C6H5C(O)O2 radicals react with NO2 with a rate constant of (1.1±0.3)×10-11 cm3 molecule-1 s-1 to form C6H5C(O)O2NO2, which undergoes thermal decomposition at a rate of k-4=(2.1-1.5+5.0)×1016 exp[-(13600±400)K/T] s-1 in one atmosphere of air. At 296 K in 100–700 Torr of air k[C6H5C(O)O2+NO]/k[C6H5C(O)2+NO2]=1.44±0.15. Relative rate methods were used to measure k[Cl+C6H5C(O)Cl]=(1.1±0.2)×10-15 cm3 molecule-1 s-1 at 296 K. Uncertainty limits are all two standard deviations. Results are discussed with respect to the literature data and the atmospheric chemistry of benzaldehyde.