Abstract:Formation of methoxy (CH30) radicals in the reaction (1) CH302 + NO ~ CH30 + NO 2 at 298 K has been observed dkectly using time resolved LIF. The branching ratio ¢CH30 (= -A[CHaO]/ A[CH302]) has been determined by quantitative cw-UV-laser absorption at 257 nm of CH30 ~ and CH~ONO, the product of the consecutive methoxy trapping reaction (2) CH30+NO(+M) CH3ONO (+M). $CH30 is found to be (1.0 -+ 0.2). The rate constant k I is (7 +-2) 10 -t2 cm3/molecule • s in good agreement with previous results.
“…In case of NO + C 2 H 5 OO, the stabilization channel to C 2 H 5 ONO 2 contributes only ∼1% at ambient conditions [110,111]. Room-temperature measurements of k 6 [106][107][108][109][112][113][114][115][116] and k 7 [99,111,115,[117][118][119] are generally in good agreement. Atkinson et al [98] proposed temperature-dependent rate expressions based on data from 200-400 K [108,109,111,118,119] with corrections to match the average values at 298 K.…”
“…In case of NO + C 2 H 5 OO, the stabilization channel to C 2 H 5 ONO 2 contributes only ∼1% at ambient conditions [110,111]. Room-temperature measurements of k 6 [106][107][108][109][112][113][114][115][116] and k 7 [99,111,115,[117][118][119] are generally in good agreement. Atkinson et al [98] proposed temperature-dependent rate expressions based on data from 200-400 K [108,109,111,118,119] with corrections to match the average values at 298 K.…”
“…Because none of the larger radicals studied here are the same as those studied by Sehested et al, it is possible there is no discrepancy between their work and ours. 3 Graphic representation of all room-temperature rate coefficient data on RO 2 + NO reactions for nonsubstituted hydrocarbon radicals given in Table : (·) this laboratory, ,,11,this work (□) CSIRO group, ,,, (○) Sander and Watson, (◆) Cox and Tyndall, (▿) Simonaitis and Heicklen, (×) Ravishankara et al., (▵) Zellner et al., (▴) Sehested et al, (*) Masaki et al., (▪) Daële et al, (▾) Maricq and Szente, and (◇) Peeters et al …”
The rate coefficients for the gas-phase reactions of allyl-,
tert-butyl-, cyclopentyl-, and 2-pentylperoxy
radicals
with NO have been measured at 297 ± 2 K in a flow tube reactor using
chemical ionization mass spectrometric
(CIMS) detection of the peroxy radical. The hydrocarbon radicals
were produced through the dissociation of
the parent alkyl iodide in a low-power radio frequency (rf) discharge.
The unimolecular decomposition of
the c-pentyl radicals in the rf discharge yielded allyl
radicals. The peroxy radicals were generated by
reacting
the hydrocarbon radicals with O2. The rate
coefficients were found to be, in units of
10-12 cm3
molecule-1
s-1, 10.5 ± 1.8, 7.9 ± 1.3, 10.9 ± 1.9,
and 8.0 ± 1.4 for the reactions of NO with
CH2CHCH2O2,
t-C4H9O2,
c-C5H9O2, and
2-C5H11O2 radicals, respectively.
The results of this study together with our previous
results
for nonsubstituted C1−C3 alkyl peroxy
radicals suggest no significant trend in the rate coefficients with
size
and branching of the radicals. This is in contradiction to some
previous studies, which found that the rate
coefficients decrease with increasing radical size and complexity.
Some implications of this finding for
atmospheric chemistry are briefly discussed.
“…established an upper limit branching ratio [ k 4b /( k 4a + k 4b )] of 0.24 for channel 4b by following the production of the channel 4a product, NO 2 , and applying mass balance arguments to determine the maximum branching into channel 4b that was consistent with the data . Zellner et al determined an upper limit of 0.20 for channel 4b by following the production of the other channel 4a product, CH 3 O, and again applying mass balance arguments to determine the maximum branching into channel 4b that was consistent with their data . In addition, Atkinson and co-workers have developed an empirical relationship for the yield of organic nitrates from environmental chamber photolysis studies of C 3 −C 9 hydrocarbon/NO mixtures at 298 K .…”
Section: Introductionmentioning
confidence: 95%
“…balance arguments to determine the maximum branching into channel 4b that was consistent with their data. 9 In addition, Atkinson and co-workers have developed an empirical relationship for the yield of organic nitrates from environmental chamber photolysis studies of C 3 -C 9 hydrocarbon/NO mixtures at 298 K. 12 Although this relationship probably provides only a qualitative estimate of potential methyl nitrate formation from reaction 4, it is important to note that the branching ratio is predicted to rise from 0.005 for the methyl case to 0.16 for the n-heptyl case at 298 K and 760 torr, thus indicating the importance of the association channel for the larger alkyl peroxy radicals.…”
Section: Introductionmentioning
confidence: 99%
“…The CH 3 O 2 + NO reaction has received considerable study − because of its important role in the formation of tropospheric ozone. In the most recent study, Villalta et al used low-pressure chemical ionization mass spectrometry (CIMS) to measure the negative temperature dependence of the rate constant to temperatures as low as 200 K. Although this study included temperatures of the upper troposphere, the experiments were carried out at low pressure (∼ 3 Torr).…”
The overall rate constant and an upper limit for the CH 3 ONO 2 product channel for the CH 3 O 2 + NO reaction have been measured using the turbulent flow technique with high-pressure chemical ionization mass spectrometry for the detection of reactants and products. At room temperature and 100 Torr pressure, the rate constant (and the two standard deviation error limit) was determined to be (7.8 ( 2.2) × 10 -12 cm 3 molecule -1 s -1 . The temperature dependence of the rate constant was investigated between 295 and 203 K at pressures of either 100 or 200 Torr, and the data was fit to the following Arrhenius expression: (9.2 -3.9+6.0 × 10 -13 ) exp[(600 ( 140)/T] cm 3 molecule -1 s -1 . Although the room-temperature rate constant value agrees well with the current recommendation for atmospheric modeling, our values for the rate constant at the lowest temperatures accessed in this study (203 K) are about 50% higher than the same recommendation. No CH 3 -ONO 2 product was detected from the CH 3 O 2 + NO reaction (using direct CH 3 ONO 2 detection methods for the first time), but an improved upper limit of 0.03 (at 295 K and 100 torr) for this branching channel was determined.
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