A quantitative study of alkyl radical reactions by kinetic spectroscopy. II. Combination of the methyl radical with the oxygen molecule

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.

Section: Methodsmentioning

confidence: 99%

“…Basco et al [5] concluded that it was possible to eliminate any plausible two-body reaction such as (41, (…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

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

Plumb

Ryan

1982

“…The rate constant for reaction (3b) has not been measured. However, the rate constant for the corresponding reaction of the methyl radical was estimated to be not much greater than 2 X lo5 liter mole-lsec-l by Basco, James, and James in 1972 [3]. A low value was confirmed both by the results of very low pressure pyrolysis studies in 1973 [lo], and by the extrapolation of an Arrhenius expression fitted to the results of eight studies of the shock-initiated oxidation of methane in a recent review [ l l ] .…”

Section: Evaluation Of K 4 F / C (X)mentioning

confidence: 99%

The ethylperoxy radical spectrum and rate constant for mutual interaction measured by flash photolysis and kinetic spectroscopy

Adachi

Basco

James

1979

Self Cite

Intrinsic spectral and kinetic parameters have been measured for the ethylperoxy radical, which was formed in the gas phase by the flash photolysis of azoethane in the presence of an adequate excess of oxygen. Absolute values of the extinction coefficient €(A) were derived from complementary measurements of the yield of nitrogen and the absorbance of an equivalent concentration of ethylperoxy radicals. The absorption spectrum is broad, structureless and comparatively weak; ~(236) = 1.02 X lo3 liter mole-' cm-I a t the maximum, and the oscillator strength is 3.4 X This spectrum resembles the spectrum of the methylperoxy radical closely in form, but it is less intense; the ratio of the values of oscillator strength is 0.5. The bimolecular reactions of mutual interaction of ethylperoxy radicals are not exclusively terminating, and ethoxy and hydroperoxy radicals are formed in kinetically significant quantities. A computer program was designed to simulate the rise and fall of the concentration of each radical species, and to perform the related kinetic analysis. This program predicted that a second-order plot of the decline of the absorbance of the ethylperoxy radical during the dark period would not show a significant departure from linearity, a conclusion which was confirmed by experiment. Accordingly, the gradient of each such plot yielded a value of k ' / t ( X ) , where k' is the apparent value of the rate constant for the collective reactions of mutual interaction. This rate constant was evaluated from the product of corresponding values of k'/c(X) and €(A); individual values are independent of the wavelength of measurement, and the mean value is k' = (6.6 f 0.5) X loT liter mole-'sec-'. Further kinetic analysis yielded the corresponding absolute value: k = (6.0 f 0.6) X lo7 liter mole-' sec-l. This value fits the pattern of a relationship between rate constant and structure shown by the methylperoxy, isopropylperoxy, and tert -butylperoxy radicals. Adequate sensitivity for the characterization of the spectrum of the ethylperoxy radical was achieved by the use of a pulsed xenon arc as the monitoring light source in conjunction with a dual beam detection system with twin cells and balanced photomultipliers, and the apparatus is described in detail.

“…These values and the fact that E2 should be low were used as a starting point for a computer fit of the experimental data with the above reaction scheme. The rate constant k 1 was taken from [28], k5 from [29], and k.3, k4 were estimated as described above. The following expressions for k ; and k2 were obtained: may be significant contributions from vibrationally excited states in hb since the reaction is endo-ergic and vibrational energy may effectively assist in surmounting the barrier.…”

Section: Ch4-fz-ar Systemmentioning

confidence: 99%

A study of the reactions of fluorine with hydrogen and methane in the initiation phase using a miniature tubular reactor

Rotzoll

Lübbert

Schügerl

1981

A small tubular reactor having an inner diameter of 1-2 mm and used as the source in a molecular beam apparatus is described in detail. This arrangement allows the study of fast reactions with reaction times smaller than 1 msec. The preexplosive reaction phase between Fz and Hz and CHI, respectively, is investigated to find out the initiation reactions. In the Fz/H2 reaction, initiation is brought about by heterogeneous generation of F atoms or some other surface reaction. Evidence is also obtained for chain branching reactions. In the F&H4 case the dominant initiation reaction is the homogeneous reaction CHI + F2 -CH:J