Theoretical Investigation of the Atmospheric Cl Oxidation Chemistry of 4-Methyl-3-penten-2-one

Abstract

The reaction mechanisms and kinetics of 4-methyl-3-penten-2-one (MPO) with atomic Cl have been studied using second-order Møller−Plesset perturbation theory (MP2) and canonical variational transition-state (CVT) theory with smallcurvature tunneling (SCT) correction methods. Eight different reaction paths are considered: two possible Cl addition reactions and six possible hydrogen abstraction reactions. The results of the theoretical investigation indicate that Cl addition dominates the initial reactions of MPO with Cl atoms, and the most energetically favorable pathway is the Cl addition to the double bond carbon adjacent to the carbonyl in the molecule. Among all of the six Habstraction paths, the H abstraction from the two methyl groups linked to the double bond is predicted to occur readily according to the calculated data. In addition, the 1,5-H shift isomerization process, involving the Cl addition mechanism, was proposed and found to be feasible. The major possible products that were detected in experiment and derived from our theoretical study have been identified. The rate constants and branching ratios of the main reaction paths have been obtained over the temperature range of 180−380 K. The total rate constants are dependent on temperature and the Arrhenius equation is fitted as k total = (2.99 × 10 −13 )exp(1795.60/T). The atmospheric lifetime is also estimated and shows a positive temperature dependence.

Theoretical Investigations of the OH-Initialized Oxidation of 4-Methyl-3-Penten-2-One in the Atmosphere

“…It has been reported that the production rate of 4M3P2O is as high as 0.1 Tg yr –1 in the US . Toxicological studies have shown that 4M3P2O can irritate eyes, skin, and mucous membrane and even cause severe damage to the liver, kidney, and central nervous system. , The release of 4M3P2O into the atmosphere is likely to have effects on tropospheric ozone levels and also lead to the formation of secondary organic aerosol particles . Accordingly, it is important that we understand the oxidation chemistry of 4M3P2O.…”