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

Abstract

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 N₂ atmosphere using C₂H₆ and C₂H₄ 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) × 10⁻¹⁶] T² exp [− (33 ± 4) / T] cm³ molecule⁻¹ s⁻¹. 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 × 10⁻¹⁶) T^1.5 exp (466 / T) cm³ molecule⁻¹ s⁻¹. 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

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