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

Abstract. Temperature dependent rate coefficients for the gas phase reactions of Cl atoms with 4-hexen-3-one and 5-hexen-2-one were measured over the temperature range of 298–363 K relative to 1-pentene, 1,3-butadiene and isoprene. Gas Chromatography (GC) was used to measure the concentrations of the organics. The derived temperature dependent Arrhenius expressions are k4-hexen-3-one+Cl (298–363 K) = (2.82 ± 1.76)×10⁻¹²exp [(1556 ± 438)/T] cm³ molecule⁻¹ s⁻¹ and k_{5-hexen-2-one+Cl} (298–363 K) = (4.6 ± 2.4)×10⁻¹¹exp[(646 ± 171)/T] cm³ molecule⁻¹ s⁻¹. The corresponding room temperature rate coefficients are (5.54 ± 0.41)×10⁻¹⁰ cm³ molecule⁻¹ s⁻¹ and (4.00 ± 0.37)×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 understand the mechanism of Cl atom reactions with unsaturated ketones, 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 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.