Kinetics of the reactions of CH₃ with O(³P) and O₂ at 295 K

Abstract

The reactions of CH3 radicals with O(3P) and 0 2 have been studied at 295 K in a gas flow reactor sampled by a mass spectrometer. For the reaction between CH3 and 0, conditions were such that [O] >> [CH3] and the methyl radicals decayed under pseudo-first-order conditions giving a rate coefficient of (1.14 f 0.29) X cm3/s. The reaction between CH3 and 0 2 was studied in separate experiments in which CH3 decayed under pseudo-first-order conditions. In this case, the rate coefficient obtained increased with increasing concentration of the helium carrier gas. This was varied over the range of 2.5-25 X 10l6 C I Y -~, resulting in value8 for the apparent two-body rate coefficient ranging from 1 X lo-" to 5.2 X cm3/s. No evidence was found for the production of HCHO by a direct two-body process involving CH3 + 0 2 , and an upper limit of 3 X cm3/s was placed on the rate coefficient for this reaction. The experimental results for the apparent two-body rate Coefficient exhibit the curvature one would expect for an association reaction in the fall-off region. Calculations used to extrapolate these measurements to the low-pressure limit yield a value for ko of (3.4 f 1.1) X lO-3l cm6/s, which is more than a factor of 2 higher than previous estimates.

Reactions of oxygen atoms with hydrocarbon radicals: a priori kinetic predictions for the CH3+ O, C2H5+ O, and C2H3+ O reactions

“…4 together with the related experimental data [1][2][3][4][5][6][7][8][9][10][11][12][13]. The dynamically corrected VRC-TST results, given by the solid line, are in remarkably good agreement with the extensive set of experimental data.…”

“…The CH 3 + O reaction, which is, in general, the most important of these reactions due to the relatively low reactivity of the CH 3 radical, has been widely studied experimentally. These studies have focussed on both the overall rate coefficient at low [1][2][3][4][5][6][7][8][9][10] and high temperatures [11][12][13], and on the product distribution [14][15][16][17]. Overall, the total rate coefficient appears to be effectively constant at 1.4 · 10 À10 cm 3 molecule À1 s À1 from room temperature all the way up to 2300 K. However, the most recent observation of the temperature 1540-7489/$ -see front matter Ó 2004 The Combustion Institute.…”

Method for the measurement of diffusion coefficients of labile gas‐phase species: The diffusion coefficient of O(3P) in He at 294 K

“…Experiments were performed using a gas-flow reactor sampled by a quadrupole mass spectrometer. A detailed description of this apparatus has been published [8], and more recently, experiments in which 0 atoms were admitted through the movable inlet have been described [9]. In the present experiments 0 atoms were produced by passing 1% oxygen in helium, diluted further with helium as required, through a microwave discharge which is fixed to the movable inlet a t a point 95 cm upstream from the point where gas from this inlet joins the main flow.…”

Kinetics and Product Study of the Reaction of CH3 Radicals with O(3P) Atoms Using Time Resolved Time-of-Flight Spectrometry

“…The kinetics of this reaction have been studied extensively − by observing either the disappearance of methyl radicals in the presence of oxygen atoms or the formation of formaldehyde as the major product. The overall rate coefficient for reaction 1 has been observed to be (1.4 ± 0.3) × 10 -10 cm 3 molecule -1 s -1 , independent of pressure and temperature .…”