Abstract:The flash photolysis of azomethane in a quartz reaction vessel produces mainly ethane (>7.53) plus smaller quantities of methane, ethylene, and acetylene. The minor products are interpreted quantitatively in terms of methyl radical photolysis at 216 nm to give CH, and H. This interpretation is substantiated by the dependence of the minor products on flash intensity. The reduction of the ethane yield on adding NO is employed to obtain a rate constant for CH3 + NO as a function of total pressure, based on a valu… Show more
“…The pressure-dependent expression of k 1 has been adopted from the work of Davies et al [77], who combined measurements of the rate constant at 296-509 K and pressures from 0.03 to 0.8 bars with a master equation approach. Room-temperature experiments [78][79][80][81][82] confirm their recommendation over a wider pressure range. The center-broadening factor was refitted in the present work in the conventional Troe format suitable for kinetic modeling with the CHEMKIN software [83].…”
“…The pressure-dependent expression of k 1 has been adopted from the work of Davies et al [77], who combined measurements of the rate constant at 296-509 K and pressures from 0.03 to 0.8 bars with a master equation approach. Room-temperature experiments [78][79][80][81][82] confirm their recommendation over a wider pressure range. The center-broadening factor was refitted in the present work in the conventional Troe format suitable for kinetic modeling with the CHEMKIN software [83].…”
“…As can be seen, the fit is acceptable. 5 Master equation fits to the CH 3 + H data of Brouard et al . Microcanonical rate coefficients calculated from (a) FTST, (b) inverse Laplace transform, and (c) at 300 K fixed to experimental value (2.9 × 10 -10 cm 3 molecule -1 s -1 ), temperature dependence of floated.…”
Section: Master Equation Modeling Of the Ch3 + H Data
Of
Brouard Et Almentioning
confidence: 99%
“…A majority of the previous determinations of the rate coefficient for reaction 1 have been indirect studies, − monitoring the methane production at low pressures from the following sequence of reactions: Higher pressure (>100 Torr) studies have been initiated by the Hg photosensitization of ethane, flash photolysis of azomethane/ethene mixtures, , or methane/water mixtures . The reaction compositions have been monitored by gas chromatographic end product analysis or mass spectrometry, an exception being the work of Sworski et al who monitored the reaction in real time using kinetic absorption spectroscopy of methyl radicals at 216 nm.…”
Section: Introductionmentioning
confidence: 99%
“…Higher pressure (>100 Torr) studies have been initiated by the Hg photosensitization of ethane, 11 flash photolysis of azomethane/ ethene mixtures, 12,13 or methane/water mixtures. 14 The reaction compositions have been monitored by gas chromatographic end product analysis or mass spectrometry, an exception being the work of Sworski et al 14 who monitored the reaction in real time using kinetic absorption spectroscopy of methyl radicals at 216 nm.…”
The reactions of methyl isotopomers (CH3,
CH2D, and CHD2) with excess deuterium atoms
have been studied
using discharge flow/mass spectrometry at 298 K and at pressures of
∼1 Torr (helium). At these low pressures
the initially formed methane complex is not stabilized. However,
zero-point energy differences between
methyl isotopomers mean that ejection of H from energized methane is
favored. In consequence, regeneration
of the reactant isotopomer is inefficient and values of
k
1a
-
c may be extracted
from the appropriate methyl
radical decay. The experimental values can be used to calculate
the high-pressure values for each isotopic
reaction: (1a) CH3 + D → CH2D + H,
= (2.3 ± 0.6) × 10-10 cm3
molecule-1 s-1;
(1b) CH2D + D →
CHD2 + H,
= (2.1 ± 0.5) × 10-10 cm3
molecule-1 s-1;
(1c) CHD2 + D → CD3 + H,
= (1.9 ± 0.5)
× 10-10 cm3
molecule-1 s-1.
These, in turn, can be corrected for isotopic substitution and
averaged to give
a value of (2.9 ± 0.7) × 10-10
cm3 molecule-1
s-1 for the limiting high-pressure
recombination rate coefficient
of CH3 and H. The errors of ∼25% are estimates of
both the statistical and systematic errors in the
measurements and calculations. The results are in agreement with
an earlier direct determination of reaction
1a and recent theoretical calculations. The previous direct
studies of CH3 + H in the fall off region
have
been reanalyzed using master equation techniques and are now shown to
be in good agreement with current
experimental and theoretical calculations. Reaction 1c was also
studied at 200 K, with k
1c falling
by
approximately 35% from its room-temperature value, confirming
theoretical predictions of a positive
temperature dependence for the high-pressure limiting rate coefficient
for the reaction CH3 + H + M →
CH4
+ M.
The reaction between CH3 radicals and NO was investigated behind incident shock waves at temperatures between 1800 and 2150 K and total densities near 2 · 10−6 mol cm−3. — The consumption of CH3 was followed by time‐resolved UV‐absorption measurements at λ = 216 nm. — A rate constant of 2·1010 cm3 mol−1 s−1 for the reaction
at temperatures around 1900 K was determined. — An activation energy of about 85 kJ mol−1 is estimate
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