Methyl Vinyl Ketone+OH and Methacrolein+OH Oxidation Reactions: A Master Equation Analysis of the Pressure‐ and Temperature‐Dependent Rate Constants

Abstract

High-level electronic structure calculations and master equation analyses were carried out to obtain the pressure- and temperature-dependent rate constants of the methyl vinyl ketone+OH and methacrolein+OH reactions. The balance between the OH addition reactions at the high-pressure limit, the OH addition reactions in the fall-off region, and the pressure-independent hydrogen abstractions involved in these multiwell and multichannel systems, has been shown to be crucial to understand the pressure and temperature dependence of each global reaction. In particular, the fall-off region of the OH addition reactions contributes to the inverse temperature dependence of the rate constants in the Arrhenius plots, leading to pressure-dependent negative activation energies. The pressure dependence of the methyl vinyl ketone+OH reaction is clearly more important than in the case of the methacrolein+OH reaction owing to the weight of the hydrogen abstraction process in this second system. Comparison of the theoretical rate constants and the experimental measurements shows quite good agreement.

Atmospheric Reaction of Cl + Methacrolein: A Theoretical Study on the Mechanism, and Pressure- and Temperature-Dependent Rate Constants

“…The energy of ap conformer is lower than that of the sp conformer by 3.5 kcal mol –1 at the HL level of theory, which is in consistent with the theoretical results performed by Ochando-Pardo et al, who obtained the ap : sp ratio of 99.6:0.4, and experimental results (97.5:2.5 and 100:0 at room temperature) also showed that the ap conformer of MACR has significant weight in its reactivity . So only the ap conformer was taken into account for the mechanism and kinetics study of the Cl + MACR reaction, just like researchers did with the OH + MACR reaction. , …”

“…47 So only the ap conformer was taken into account for the mechanism and kinetics study of the Cl + MACR reaction, just like researchers did with the OH + MACR reaction. 8,9 From the geometric structure of MACR shown in Figure 1, we can see that the Cl atom may react with MACR by the following possible paths: (1) addition, the Cl atom adds to the CC or the CO double bonds; (2) hydrogen atom abstraction, the Cl atom abstracts the aldehyde-H, the methyl-H, or the methylene-H atoms; (3) group abstraction, the Cl atom abstracts the −CH 3 or the −HCO group. In order to acquire the comprehensive reaction mechanism on which the kinetics calculation is based, we tried to calculate all of the above possible paths.…”

“…The biogenic volatile organic compounds, especially isoprene can undergo photolysis or chemical degradation by many species such as OH, O 3 , NO 3 , and Cl atoms. As one of isoprene’s major oxidation products, methacrolein (MACR) is also highly reactive toward OH, − O 3 , − NO 3 , − and Cl, − and is mainly degraded by the reaction with OH radical in atmosphere. However, large amounts of reactive chlorine compounds (ClNO 2 ), gaseous photolytic Cl atoms precursor, have been observed in continental regions far from marine and coastal regions .…”

Kinetic Study on the Reaction of OH Radical with Dimethyl Sulfide in the Absence of Oxygen

“…On the other hand, and according to a discussion by some of us, [65] this pressure dependence of a bimolecular reaction initiated by a recombination process like AD formation in the (R1ac) channel or RC formation in the indirect H-abstraction process is closely related to the depth of the well corresponding to the prereactive complex. In two competitive reactions, like (R1ac) and indirect H-abstraction, the probability of suffering deactivating collisions is higher for the adduct of the reaction with the deeper well and thus lower pressures are required to stabilize the adduct.…”

Gas-Phase Reactions of Isoprene and Its Major Oxidation Products

“…A number of studies have measured the reaction rate coefficient, k MVK+OH , over a wide range of pressure and temperature. ,,− A negative temperature dependence was widely observed over a pressure range of 6–400 hPa. ,, Dependence of k MVK+OH on pressure at 2–7 hPa was both observed and predicted in the temperature range of 300–425 K. , The reported values of k MVK+OH in the high pressure limit at room temperature are in good agreement ∼2 × 10 –11 cm 3 molecule –1 s –1 ). Here, we use the IUPAC recommendation of k MVK+OH = (2.6 × 10 –12 )­e (610 K/ T ) cm 3 molecule –1 s –1 (Table ).…”