Gas-phase reaction of two unsaturated ketones with atomic Cl and O3: kinetics and products

Abstract

The rate constants and products for the reactions of atomic Cl and O₃ molecule with 3-methyl-3-buten-2-one (MBO332) and 3-methyl-3-penten-2-one (MPO332) were determined in a 100 L Teflon chamber at 293 ± 1 K and atmospheric pressure. For MBO332 and MPO332, the rate constants measured with atomic Cl were (2.38 ± 0.26) × 10⁻¹⁰ and (3.00 ± 0.34) × 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹ using the relative rate method. Using the absolute rate method, the rate constants with O₃ measured were (1.18 ± 0.21) × 10⁻¹⁷ and (4.07 ± 0.45) × 10⁻¹⁷ cm³ molecule⁻¹ s⁻¹. The products of these reactions were investigated by the proton-transfer-reaction mass spectrum (PTR-MS). The results indicated that the major products observed in the atomic Cl reaction were formaldehyde together with chloroacetone for MBO332, and acetaldehyde and CH₃C(O)C(O)Cl for MPO332. For O₃ reactions, butanedione and formaldehyde were the main products of MBO332, while butanedione and acetaldehyde were the main products of MPO332. Possible reaction mechanisms were proposed and discussed and the atmospheric implications of these reactions were also discussed.