Kinetics, products and mechanisms of the OH radicals and Cl atoms reactions with trans-2-octene and cycloheptene.

Abstract

Relative rate coefficients for the gas-phase reactions of OH radicals and Cl atoms with trans-2-octene (k1-OH and k2-Cl) and cycloheptene (k3-OH and k4-Cl) have been determined by in situ Fourier Transform Infrared Spectroscopy (FTIR). The experiments were carried out at 298 ± 2 K and atmospheric pressure (760 ± 10) Torr using synthetic air as bath gas. The following rate coefficients (in units of cm3 molecule-1 s-1) were obtained for the reactions of trans-2-octene and cycloheptene with OH radicals and Cl atoms: k1-OH = (8.51 ± 1.86)×10-11, k2-Cl = (4.47 ± 1.09)×10-10, k3-OH = (7.84 ± 1.78)×10-11, k4-Cl = (5.46 ± 1.01)×10-10, respectively. This is the first kinetic study for the reactions of trans-2-octene with Cl atoms and the first rate coefficient determination for the title reactions by in situ FTIR spectroscopy. The kinetic data were compared with previously reported values for similar compounds and reactivity trends were developed. Complementary, products identification studies were performed in similar conditions to the kinetic experiments by the in situ FTIR and Gas Chromatography coupled to mass spectrometry (GC-MS). The atmospheric chemical mechanisms were postulated for the first time for both unsaturated compounds. In addition, the atmospheric implications of these reactions were assessed through the estimation of the tropospheric lifetimes, Photochemical Ozone Creation Potential (POCP) and fates of these compounds in the troposphere.