Experimental and computational kinetic investigations for the reactions of Cl atoms with unsaturated ketones in the gas phase

Temperature dependent rate coefficients for the gas phase reactions of Cl atoms with 4-hexen-3-one and 5-hexen-2-one were measured as a function of temperature (298-363 K) and pressure (500-760 Torr; N2 and O2) relative to 1,3-butadiene, isoprene and 1-pentene. Gas Chromatography (GC) coupled with a Flame Ionization Detector (FID) was used to measure the concentrations of the organics. The derived temperature dependent Arrhenius expressions are k1 = (2.82 ± 1.76) × 10-12 exp [(1556 ± 438)/T] cm3 molecule-1 s-1 and k2 = (4.6 ± 2.4) × 10-11 exp [(646 ± 171)/T] cm3 molecule-1 s-1. The corresponding room temperature rate coefficients are (5.55 ± 1.31) × 10-10 cm3 molecule-1 s-1 and (4.14 ± 1.25) × 10-10 cm3 molecule-1 s-1 for the reactions of Cl atoms with 4-hexen-3-one and 5-hexen-2-one respectively. To complement our experimental results, computational calculations were performed for the reactions of Cl atoms with 4-hexen-3-one, 5-hexen-2-one and 3-penten-2-one over the temperature range of 275-400 K using Canonical Variational Transition state theory (CVT) with Small Curvature Tunneling (SCT) in combination with the CCSD(T)/6-31+G(d,p)//MP2/6-311++G(d,p) level of theory. Atmospheric implications, reaction mechanism and feasibility of the title reactions are discussed in this manuscript.