Computational study of the methyl + oxygen chain branching reaction

Abstract

Rate constants and branching ratio for the reaction channels CH3 + 02 -»• CH30 + O (la) and CH3 + 02 -* CH20 + OH (lb) have been derived from RRKM theory by assuming a common CH302 intermediate. The computation is based on a 160 kJ /mol isomerization barrier between CH302 and CH2OOH as derived recently in direct studies of the reverse CH30 + O reaction at low temperatures. In contrast to most previous conclusions, channel lb is predicted to dominate over channel la at all temperatures below 2800 K, with the individual rate coefficients being kH= 1.1 X 1013 exp(-13990/T) and klb = 3.4 X 1011 exp(-4500/T) cm1 23 4567/(rnol-s).

An Investigation of the Reaction of CH3 Radicals with O2 at High Temperatures

“…exp(-15060 K / T ) cm3/mol s for AHioo (CH30) = 22 kJ/mol. Both expressions are consistent with both sets of measurements used within the limits of experimental error and both give a very small temperature dependence of the reaction CH,O + 0 -, CH, + O2 as computed by [7,21]. Complete agreement with the computed shape for the reverse reaction can easily be obtained with a slightly upwards curved Arrhenius expression for reaction (1 a) (see [7]).…”

“…The size of this rate constant excludes a larger activation energy for this reaction channel. Calculations performed on the basis of the theory of unimolecular reactions by Cobos et al [21] (SACM) and Ewig et al [7] (RRKM) indicate that this rate constant should be nearly independent of temperature, with a slight increase towards 2000 K. At room temperature theory and experiment give similar values of the rate constant. It is therefore to be expected, that the measured apparent energy of activation for reaction (1 a) should be close to the reaction enthalpy, which is 2 119 kJ/mol.…”

“…On the one hand there are the results of Bhaskaran et al [4] which were obtained from 0 and H atom profiles in shock waves, those of Fraatz [8] which are based on simulations of measured CH3 and OH profiles, the results computed by Teitelboim et al [6] and the data reported by Ewig et al [7] which were derived from measurements of C H 3 0 + 0 -P CH3 + O2 at room temperature.…”

“…While using reaction (1) as a source of NO3 radicals, F-atoms have been produced either by photolysis [7] or by microwave discharge [9-121. Reaction (l), like most hydrogen abstraction reactions by atomic fluorine, is very fast and early workers used it with excess H N 0 3 in their systems to produce NO3 radicals for spectroscopic studies.…”

Environmental effects of large igneous province magmatism: a Siberian perspective

“…This reaction has been studied by only Bridier et al [177] and Tyndall et al based their recommendation on this one study. (Table: [1514] suggests that this reaction is important at combustion temperature but is unimportant for the atmosphere. (Table 83 [1293], and Ninomiya et al [996].…”