Cl-initiated photo-oxidation reactions of methyl propionate in atmospheric condition.

Cl-initiated photo-oxidation reaction of methyl propionate was investigated experimentally using relative rate method. Gas chromatography/mass spectrometry (GC-MS) and GC/infrared spectroscopy (GC-IR) were used as analytical tools to follow the concentrations of reactants and products during reaction. The gas-phase kinetics of methyl propionate with Cl atoms was measured over the temperature range of 263-363 K at 760 Torr in N atmosphere using CH and CH as reference compounds. The temperature-dependent rate coefficient for the reaction of methyl propionate with Cl atom was obtained as k(T) = [(3.25 ± 1.23) × 10] T exp [- (33 ± 4) / T] cm molecule s. Theoretical calculations were also performed at CCSD(T)/cc-pVDZ//B3LYP/6-31G(d,p) level of theory, and the rate coefficients for H abstraction reactions were evaluated using canonical variational transition state theory (CVT/SCT) with interpolated single point energy (ISPE) method over the temperature range of 200-400 K. The rate coefficients over the studied temperature range yielded the Arrhenius expression k(T) = (7.22 × 10) T exp (466 / T) cm molecule s. The reaction mechanism based on product analysis, thermochemistry, branching ratios, atmospheric implications, degradation pathways, and cumulative lifetime of methyl propionate is also presented in this manuscript. Graphical abstract ᅟ.