Kinetics of the brominated alkyl radical (CHBr 2 , CH 3 CHBr) reactions with NO 2 in the temperature range 250-480 K (original) (raw)
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The Journal of Physical Chemistry A, 2005
The kinetics of the reactions of chlorinated methyl radicals (CH 2 Cl, CHCl 2 , and CCl 3 ) with NO 2 have been studied in direct measurements at temperatures between 220 and 360 K using a tubular flow reactor coupled to a photoionization mass spectrometer. The radicals have been homogeneously generated at 193 or 248 nm by pulsed laser photolysis of appropriate precursors. Decays of radical concentrations have been monitored in time-resolved measurements to obtain the reaction rate coefficients under pseudo-first-order conditions with the amount of NO 2 being in large excess over radical concentrations. The bimolecular rate coefficients of all three reactions are independent of the bath gas (He or N 2 ) and pressure within the experimental range (1-6 Torr) and are found to depend on temperature as follows: k(CH 2 Cl + NO 2 ) ) (2.16 ( 0.08) × 10 -11 (T/300 K) -1.12(0.24 cm 3 molecule -1 s -1 (220-363 K), k(CHCl 2 + NO 2 ) ) (8.90 ( 0.16) × 10 -12 (T/300 K) -1.48(0.13 cm 3 molecule -1 s -1 (220-363 K), and k(CCl 3 + NO 2 ) ) (3.35 ( 0.10) × 10 -12 (T/300 K) -2.2(0.4 cm 3 molecule -1 s -1 (298-363 K), with the uncertainties given as one-standard deviations. Estimated overall uncertainties in the measured bimolecular reaction rate coefficients are about (25%. In the reactions CH 2 Cl + NO 2 , CHCl 2 + NO 2 , and CCl 3 + NO 2 , the products observed are formaldehyde, CHClO, and phosgene (CCl 2 O), respectively. In addition, a weak signal for the HCl formation has been detected for the CHCl 2 + NO 2 reaction.
The Journal of Physical Chemistry A, 2009
The gas-phase kinetics of three ethyl radical reactions with NO 2 have been studied in direct measurements using a laser photolysis/photoionization mass spectrometer (LP-PIMS) coupled to a temperature controlled tubular flow reactor. Reactions were studied under pseudo-first-order conditions with NO 2 always in large excess over initial radical concentrations. All the measured rate coefficients exhibit a negative temperature dependence, which becomes stronger as the chlorine substitution in the R-carbon of the ethyl radical increases. No pressure dependence of the rate coefficients was observed within the experimental range covered (0.5-6 Torr). The obtained results can be expressed conveniently as follows: k(CH 3 CH 2 + NO 2 ) ) (4.33 ( 0.13) × 10 -11 (T/300 K) -0.34 ( 0.22 cm 3 s -1 (221-365 K), k(CH 3 CHCl + NO 2 ) ) (2.38 ( 0.10) × 10 -11 (T/300 K) -1.27 ( 0.26 cm 3 s -1 (221-363 K), and k(CH 3 CCl 2 + NO 2 ) ) (1.01 ( 0.02) × 10 -11 (T/300 K) -1.65 ( 0.19 cm 3 s -1 (248-363 K), where the given error limits are the 1σ statistical uncertainties of the plots of log k against log(T/300 K). Overall uncertainties in the measured rate coefficients were estimated to be (20%. The observed reactivity toward NO 2 decreases with increasing chlorine substitution at the radical site as was expected with respect to our previous measurements of chlorine containing methyl radical reactions with NO 2 . A potential reason for the observed reactivity differences is briefly discussed, and a possible reaction mechanism is presented.
Journal of Physical Chemistry A, 1999
Reactions of methyl radicals with hydrogen bromide CH 3 + HBr f CH 4 + Br (1) and bromine atoms CH 3 + Br f CH 3 Br (2) were studied using excimer laser photolysis-transient UV spectroscopy at 297 ( 3 K over the 1-100 bar buffer gas (He) pressure range. Methyl radicals were produced by 193 nm (ArF) laser photolysis of acetone, (CH 3 ) 2 CO, and methyl bromide, CH 3 Br. Temporal profiles of methyl radicals were monitored by UV absorption at 216.51 nm (copper hollow cathode lamp with current boosting). The yield of acetyl radicals in photolysis of acetone at 193 nm was found to be less than 5% at 100 bar He based on the transient absorptions at 222.57 and 224.42 nm. The measured rate constants for reaction 1 are k 1 ) (2.9 ( 0.7) × 10 -12 , (3.8 ( 1.5) × 10 -12 , and (3.4 ( 1.3) × 10 -12 cm 3 molecule -1 s -1 at the buffer gas (He) pressures of 1.05, 11.2, and 101 bar, respectively. The rate data obtained in this study confirmed high values of the previous (low pressure) measurements and ruled out the possibility of interference of excited species. The measured rate constant is independent of pressure within the experimental error. The rate constant of reaction of methyl radicals with bromine atoms (2) was determined relative to the rate constant of methyl radical self-reaction, CH 3 + CH 3 f C 2 H 6 (3) in experiments with photolysis of CH 3 Br: k 2 /k 3 ) 0.92 ( 0.32, 1.15 ( 0.30, and 1.65 ( 0.26 at 1.05, 11.2, and 101 bar He, respectively. On the basis of the literature data for reaction 3, this yields k 2
Environmental Science & Technology, 1985
H Rate constants for the gas-phase reactions of OH radicals with biphenyl and the monochlorobiphenyls have been determined by using a relative rate technique in 1 atm of air at 295 f 1 K. The rate constants obtained, relative to a rate constant for the reaction of OH radicals with cyclohexane of (7.57 f 0.05) X cm3 molecule-' s-' , were the following (in units of X10-l2 cm3 molecule-' s-9: biphenyl, 8.5 f 0.8; 2-chlorobiphenyl, 2.9 f 0.4; 3chlorobiphenyl, 5.4 f 0.8; 4-chlorobiphenyl, 3.9 f 0.7. These rate constants lead to estimated atmospheric lifetimes due to reaction with the OH radical of-2.7,-8,-4, and-6 days for biphenyl and 2-, 3-, and 4-chlorobiphenyl, respectively, for a 24-h average OH radical concentration of 5 x IO5 cm- ,.
Kinetic Study of the Gas Phase Reactions of a Series of Alcohols with the NO 3 Radical
The Journal of Physical Chemistry A, 2012
The rate coefficients for the reaction of NO 3 radical with 2-butanol, 3-methyl-2-butanol, and 2,3-dimethyl-2butanol were determined using relative rate technique in a 50 L glass pyrex photoreactor using in situ FT-IR spectroscopy at room temperature and a pressure of 350−670 Torr. The rate coefficient for the reaction of 2-methyl-2-butanol with NO 3 radical was also determined using, in this case, GC/MS. The rate coefficients calculated (in units of cm 3 molecule −1 s −1) were (2.51 ± 0.42) × 10 −15 , (3.06 ± 0.52) × 10 −15 , (2.67 ± 0.3) × 10 −15 , and (1.57 ± 0.16) × 10 −15 , respectively. Results indicate that the reaction occurs by an initial H-abstraction of the alcohols by the NO 3 radical and that NO 3 is more reactive toward a H atom attached to a tertiary carbon than that attached to a secondary or primary carbon. Results are also discussed as related to their homologous structural alkanes and in comparison with the reactivity of other atmospheric oxidants. Atmospheric relevance of the considered reactions is evaluated, concluding that they are potential ozone generators, they have no significant influence on global warming, and the dominant atmospheric loss process for these alcohols is their daytime reaction with OH radicals.
Journal of Atmospheric Chemistry, 1999
The aim of this work is to study the reactivity of some naturally emitted terpenes, 2-carene, sabinene, myrcene, α-phellandrene, d-limonene, terpinolene and γ-terpinene, towards NO3 radical to evaluate the importance of these reactions in the atmosphere and their atmospheric impact. The experiments with these monoterpenes have been carried out under second-order kinetic conditions over the range of temperature 298–433 K, using a discharge flow system and monitoring the NO3 radical by Laser Induced Fluorescence (LIF). This work is the first temperature dependence study for the reactions of the nitrate radical with the above-mentioned monoterpenes. The measured rate constants at 298 K for the reaction of NO3 with such terpenes are as follows: 2-carene, 16.6 ± 1.8, sabinene 10.7 ± 1.6, myrcene 12.8 ± 1.1, α-phellandrene 42 ± 10, d-limonene 9.4 ± 0.9, terpinolene 52 ± 9 and γ-terpinene 24 ± 7, in units of 10-12 cm3 molecule-1 s-1. The proposed Arrhenius expressions, for the reactions of NO3 with 2-carene, sabinene, myrcene and α-phellandrene are, respectively k1 = (1.4 ± 0.7) × 10-12 exp[(741 ± 190/T)] (cm3 molecule-1 s-1), k2=(2.3 ± 1.3) × 10-10 exp[−(940 ± 200/T)] (cm3 molecule-1 s-1), k3 = (2.2 ± 0.2) × 10-12 exp[(523 ± 35/T)] (cm3 molecule1 s-1) and k4 = (1.9 ± 1.3) × 10-9 exp[−(1158 ± 270/T)] (cm3 molecule-1 s-1). A decrease in the rate constants when raising the temperature has also been found for the reaction of d-limonene with NO3 while an increase in the rate constant with temperature has been observed for the reactions of terpinolene and γ-terpinene with NO3. Tropospheric half-lives for these terpenes have been calculated at night and during the day for typical NO3 and OH concentrations showing that both radicals provide an effective tropospheric sink for these compounds and that the night-time reaction with NO3 radical can be an important, if not dominant, loss process for these naturally emitted organics and for NO3 radicals.
Kinetics of resonance stabilized CH3CCCH2 radical reactions with NO and NO2
Chemical Physics Letters, 2012
The gas phase kinetics of CH 3 CCCH 2 radical reactions with NO and NO 2 have been studied in direct timeresolved measurements using temperature controlled flow tube reactors coupled to a laser photolysis/photoionization mass spectrometer. Rate coefficients of both reactions were observed to display negative temperature dependence which for the NO 2 reaction can be represented with k (CH 3 CCCH 2 + NO 2 ) = (3.97 ± 0.10) Â 10 À11 Â (T/300 K) À1.43 ± 0.12 cm 3 s À1 (221À363 K). The bath gas pressure dependence observed in the NO reaction required a pressure falloff parameterization to express the obtained rate coefficients (273À363 K). The association product C 4 H 5 NO was directly observed in the NO reaction and a product with a formula C 4 H 5 O was recorded in the NO 2 reaction.
First experimental kinetic study of the atmospherically important reaction of BrHg + NO2
Chemical Physics Letters, 2020
Atomic bromine is known to dominate the oxidation of Hg(0) to Hg(II) via a two-step process in the atmosphereformation of BrHg and subsequent reactions of BrHg with atmospheric radicals, particularly NO 2. We report the first experimental determination of the rate constants for this reaction, which we measured versus temperature (313-373 K) and pressure (80-700 Torr) using laser photolysis-laser induced fluorescence (LP-LIF). Rate constants for addition are 3-11 times lower than those predicted by a previous computational study. We also confirm the existence of competing channel, which we assign to the predicted mercury reduction reaction.
Gas Phase Kinetics and Equilibrium of Allyl Radical Reactions with NO and NO 2
The Journal of Physical Chemistry A, 2013
Allyl radical reactions with NO and NO 2 were studied in direct, time-resolved experiments in a temperature controlled tubular flow reactor connected to a laser photolysis/photoionization mass spectrometer (LP-PIMS). In the C 3 H 5 + NO reaction 1, a dependence on the bath gas density was observed in the determined rate coefficients and pressure falloff parametrizations were performed. The obtained rate coefficients vary between 0.30− 14.2 × 10 −12 cm 3 s −1 (T = 188−363 K, p = 0.39−23.78 Torr He) and possess a negative temperature dependence. The rate coefficients of the C 3 H 5 + NO 2 reaction 2 did not show a dependence on the bath gas density in the range used (p = 0.47−3.38 Torr, T = 201−363 K), and they can be expressed as a function of temperature with k(C 3 H 5 + NO 2 ) = (3.97 ± 0.84) × 10 −11 × (T/300 K) −1.55±0.05 cm 3 s −1 . In the C 3 H 5 + NO reaction, above 410 K the observed C 3 H 5 radical signal did not decay to the signal background, indicating equilibrium between C 3 H 5 + NO and C 3 H 5 NO. This allowed the C 3 H 5 + NO ⇄ C 3 H 5 NO equilibrium to be studied and the equilibrium constants of the reaction between 414 and 500 K to be determined. With the standard second-and third-law analysis, the enthalpy and entropy of the C 3 H 5 + NO ⇄ C 3 H 5 NO reaction were obtained. Combined with the calculated standard entropy of reaction (ΔS°2 98 = 137.2 J mol −1 K −1 ), the third-law analysis resulted in ΔH°2 98 = 102.4 ± 3.2 kJ mol −1 for the C 3 H 5 −NO bond dissociation enthalpy.