Room temperature rate coefficient for the reaction between CH3O2 and NO3

The molecular modulation spectroscopic technique was employed to study the kinetics of NO₃ radicals produced in the 253.7 nm photolysis of flowing gas mixtures of HNO₃/CH₄/O₂ at room temperature. By computer fitting of the NO₃ temporal behavior, a rate coefficient of (2.3 ± 0.7) × 10^?12 cm³ molecule^?1 s^?1 was obtained for the reaction between NO₃ and CH₃O₂ at 298 K.     

Rate coefficients for the gas‐phase reaction of isoprene with NO3 and NO2

Rate coefficients for the gas‐phase reaction of isoprene with nitrate radicals and with nitrogen dioxide were determined. A Teflon collapsible chamber with solid phase micro extraction (SPME) for sampling and gas chromatography with flame ionization detection (GC/FID) and a glass reactor with long‐path FTIR spectroscopy were used to study the NO₃ radical reaction using the relative rate technique with trans‐2‐butene and 2‐buten‐1‐ol (crotyl alcohol) as reference compounds. The rate coefficients obtained are k(isoprene + NO₃) = (5.3 ± 0.2) × 10^?13 and k(isoprene + NO₃) = (7.3 ± 0.9) × 10^?13 for the reference compounds trans‐2‐butene and 2‐buten‐1‐ol, respectively. The NO₂ reaction was studied using the glass reactor and FTIR spectroscopy under pseudo‐first‐order reaction conditions with both isoprene and NO₂ in excess over the other reactant. The obtained rate coefficient was k(isoprene + NO₂) = (1.15 ± 0.08) × 10^?19. The apparent rate coefficient for the isoprene and NO₂ reaction in air when NO₂ decay was followed was (1.5 ± 0.2) × 10^?19. The discrepancy is explained by the fast formation of peroxy nitrates. Nitro‐ and nitrito‐substituted isoprene and isoprene‐peroxynitrate were tentatively identified products from this reaction. All experiments were conducted at room temperature and at atmospheric pressure in nitrogen or synthetic air. All rate coefficients are in units of cm³ molecule^?1 s^?1, and the errors are three standard deviations from a linear least square analyses of the experimental data. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 37: 57–65, 2005     

Kinetics of the brominated alkyl radical (CHBr2, CH3CHBr) reactions with NO2 in the temperature range 250–480 K

The gas‐phase kinetics of CHBr₂ + NO₂ and CH₃CHBr + NO₂ reactions have been studied in direct time resolved measurements using a tubular flow reactor coupled to a photoionization mass spectrometer. The radicals were generated by pulsed laser photolysis of bromoform and 1,1‐dibromoethane at 248 nm. The subsequent decays of the radical concentrations were monitored as a function of [NO₂] under pseudo–first‐order conditions. The rate coefficients of both reactions are independent of bath gas (He) pressure and display negative temperature dependence under the conditions of 2–6 Torr pressure (He) and 250–480 K. The obtained bimolecular rate coefficients are k(CHBr₂ + NO₂) = (9.8 ± 0.4) × 10^?12 (T/300 K)^{?1.65 ± 0.18} cm³ s^?1 (288–483 K) and k(CH₃CHBr + NO₂) = (2.27 ± 0.06) × 10^?11 (T/300 K)^{?1.28 ± 0.11} cm³ s^?1 (250–483 K), with the uncertainties given as one standard error. Estimated overall uncertainties in the measured bimolecular reaction rate coefficients are ±25%. The reaction products identified were CBr₂O for the CHBr₂ + NO₂ reaction and CHBrO and CH₃CHO with minor amounts of CH₃ for the CH₃CHBr + NO₂ reaction, respectively. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 767–777, 2012     

Flash photolysis study for reactions of NO3· with sulfur compounds in acetonitrile solution

The rate constants for the reaction of NO₃· with sulfur compounds in acetonitrile have been determined by the flash photolysis method. The rate constant for dimethyl sulfone (2.7 × 10⁴ M^?1s^?1 at ?10°C) is larger than that of the deuterium derivative, indicating that NO₃· abstracts the hydrogen atom from dimethyl sulfone. In the case of dimethyl sulfide, the rate constant was evaluated to be 1.5 × 10⁹ M^?1 s^?1 at ?10°C; the transient absorption band attributable to the cation radical was observed after the decay of NO₃·, suggesting the electron transfer reaction from the sulfide to NO₃·. For diphenyl sulfide and dimethyl disulfide, the electron transfer reactions were also confirmed. For dimethyl sulfoxide, the reaction rate constant of 1.2 × 10⁹ M^?1 s^?1 (at ?10°C) was not practically affected by the deuterium substitution, suggesting that NO₃· adds to sulfur atom forming (CH₃)₂?(O)-ONO₂. On the other hand, for diphenyl sulfoxide, the electron transfer reaction occurs. By the comparison of these rate constants in acetonitrile solution with the reported rate constants in the gas phase, the change of the reaction paths was revealed.     

An indirect measurement of the absolute rate constant of the self-reaction of tert-butoxy radicals

No reliable rate constant is available for the self-reaction of tert-;butoxy radicals. We have set up a competition between hydrogen abstraction and self-reaction of tert-butoxy radicals in a flash photolysis electron spin resonance study to extract this information. Experimental values of hydrogen abstraction product radical concentrations under various hydrogen donor concentrations were then compared with theoretically calculated values with different values of 2k₄ to obtain the best fit. Hydrogen donors such as cyclopentane, anisole, methyl tert-butyl ether, and methanol were chosen for the study. A value of (1.3 ± 0.5) × 10⁹M^?1 sec^?1 for the rate constant of the self-reaction of tert-butoxy radicals has been determined at 293°K.     

Atmospheric chemistry of FCOx radicals: Kinetic and mechanistic study of the FC(O)O2 + NO2 reaction

A pulse radiolysis system was used to study the kinetics of the reaction of FC(O)O₂ radicals with NO₂. By monitoring the rate of the decay of NO₂ using its absorption at 400 nm the reaction rate constant was determined to be (5.5 ± 0.6) × 10^?12 cm³ molecule^?1 s^?1 at 296 K and 500–1000 mbar pressure of SF₆ diluent. A long path length Fourier transform infrared spectrometer was used to investigate the thermal stability of the product FC(O)O₂NO₂. The rate of thermal decomposition of FC(O)O₂NO₂ was independent of the total pressure of N₂ diluent over the range 100–700 torr and was fit by the expression k_?3 = 6.0 × 10¹⁶ exp(?14150/T) s^?1. The results are discussed in the context of the atmospheric chemistry of FCO_x radicals. © 1995 John Wiley & Sons, Inc.     

Formation of nitrous acid and nitric oxide in the heterogeneous dark reaction of nitrogen dioxide and water vapor in a smog chamber

The dark reaction of NO_x and H₂O vapor in 1 atm of air was studied for the purpose of elucidating the recently discussed unknown radical source in smog chambers. Nitrous acid and nitric oxide were found to be formed by the reaction of NO₂ and H₂O in an evacuable and bakable smog chamber. No nitric acid was observed in the gas phase. The reaction is not stoichiometric and is thought to be a heterogeneous wall reaction. The reaction rate is first order with respect to NO₂ and H₂O, and the concentrations of HONO and NO initially increase linearly with time. The same reaction proceeds with a different rate constant in a quartz cell, and the reaction of NO₂ and H₂¹⁸O gave H¹⁸ONO exclusively. Taking into consideration the heterogeneous reaction of NO₂ and H₂O, the upper limit of the rate constant of the third-order reaction NO + NO₂ + H₂O → 2HONO was deduced to be (3.0 ± 1.4) × 10^?10 ppm^?2-min^?1, which is one order of magnitude smaller than the previously reported value. Nitrous acid formed by the heterogeneous dark reaction of NO₂ and H₂O should contribute significantly to both an initially present HONO and a continuous supply of OH radicals by photolysis in smog chamber experiments.     

Kinetic Studies of Nitrate Radicals: Flash Photolysis at 193 nm

Nitrate radicals, NO₃, were produced for the first time by 193 nm laser flash photolysis of N₂O₅ and HNO₃. Detection was achieved due to NO₃'s strong absorption at 622.7 nm confirmed by measurements of the absorption spectrum in the range of 617–625 nm using both NO₃ precursors. Time‐resolved kinetic studies allowed the determination of room temperature rate coefficients for the reactions of NO₃ with 2‐methylbut‐2‐ene and NO₂ of (1.28 ± 0.11) × 10^?11 and (8.4 ± 1.2) × 10^?13 cm³ molecule^?1 s^?1, respectively. The rate coefficients compare well to previous measurements with alternative techniques, suggesting that the reported method is valid and may be applied in follow‐up studies. The rate coefficient for 2‐methylbut‐2‐ene is compared to previous measurements and predictions for the alkene as well as the related alkenol. The new data are consistent with a previously suggested deactivation of the reactive site of the double bond if adjacent to an OH group. A calculated atmospheric lifetime for 2‐methylbut‐2‐ene with respect to NO₃‐initiated oxidation of less than 3 min suggests predominant removal by NO₃ in the atmosphere.     

Study of the HNO + HNO and HNO + NO reactions by intracavity laser spectroscopy

Flash photolysis of CH₃CHO and H₂CO in the presence of NO has been investigated by the intracavity laser spectroscopy technique. The decay of HNO formed by the reaction HCO + NO → HNO + CO was studied at NO pressures of 6.8–380 torr. At low NO pressure HNO was found to decay by the reaction HNO + HNO → N₂O + H₂O. The rate constant of this reaction was determined to be k₁ = (1.5 ± 0.8) × 10^?15 cm³/s. At high NO pressure the reaction HNO + NO → products was more important, and its rate constant was measured to be k₂ = (5 ± 1.5) × 10^?19 cm³/s. NO₂ was detected as one of the products of this reaction. Alternative mechanisms for this reaction are discussed.     

Rate constants for the reactions of HCCCO and NCCO radicals with molecular oxygen

Reactions of HCCCO and NCCO radicals with O₂ have been studied by a combination of pulsed laser photolysis and photoionization mass spectrometry. HCCCO was produced by 193‐nm photolysis of methylpropiolate or 3‐butyn‐2‐one, and NCCO was formed by 193‐nm photolysis of acetylcyanide. The rate constants obtained at 298 ± 3 K were (6.5 ± 0.7) × 10^?12 cm³ molecule^?1 s^?1 for the HCCCO + O₂ reaction, and no pressure dependence was observed between 1.5 and 16 Torr of N₂ as a bath gas. Because HCO and HCCO radicals were observed as reaction products, it was confirmed that the reaction proceeds by a two‐body reaction. On the other hand, the rate constants of NCCO with O₂ depended on the total pressure and were (5.4–8.8) × 10^?13 cm³ molecule^?1 s^?1 for total pressures 2.0–15.5 Torr of N₂, confirming that the reaction proceeds by a three‐body process. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 440–448, 2001     

High-pressure range of the recombination O + O2 → O3

The recombination reaction O + O₂ → O₃ was studied by laser flash photolysis of pure O₂ in the pressure range 3–20 atm, and of N₂O? O₂ mixtures in the bath gases Ar, N₂, (CO₂, and SF₆) in the pressure range 3–200 atm. Fall-off curves of the reaction have been derived. Low-pressure rate coefficients were found to agree well with literature data. A high-pressure rate coefficient of k_∞ = (2.8 ± 1.0) × 10^?12 cm³ molecule^?1 s^?1 was obtained by extrapolation.     

Kinetics and mechanisms of the reaction of OH radicals with dimethyl sulfide

The rate constant of the reaction of OH with DMS has been measured relative to OH + ethene in a 420 l reaction chamber at 760 torr total pressure and 298 ± 3 K in N₂ + O₂ buffer gas using the 254 nm photolysis of H₂O₂ as the OH source. In agreement with a recent absolute rate determination of the reaction the measured effective rate constant was found to increase with increasing partial pressure of O₂ in the system, for 760 torr air a rate constant of (8.0 ± 0.5) × 10^?12 cm³ s^?1 was obtained. Product studies have been performed on the reaction in air using FTIR absorption spectrometry for detection of reactants and products. On a molar basis, SO₂ was formed with a yield of 70% and dimethyl sulfone (CH₃SO₂CH₃) with a yield of approximately 20%. These results are considerably different to those obtained in other product studies which were carried out in the presence of NO_x. These differences are compared and their relevance for the atmospheric oxidation mechanisms of DMS is discussed.     

Reaction of the NO3 radical with CO: Determination of an upper limit for the rate constant using FTIR spectroscopy

An upper limit for the reaction rate of CO with the nitrate radical NO₃ has been determined equal to 4 × 10^?19 cm⁺³ molec^?1 s^?1 at 295 ± 2 K. In the experiment the isotopic species C¹³O¹⁶ and C¹³O¹⁸ mixed at 1–2 ppmv level in synthetic air have been reacted with NO₃ and the reaction followed using long path infrared absorption FT spectroscopy. The result is of interest in the studies on the role played by NO₃ in nighttime tropospheric chemistry.     

The rate coefficients for the thermal decomposition of CCl3O2NO2

The thermal decomposition of CCl₃O₂NO₂ has been reevaluated based on new rate data for the reaction of Cl + NO₂. The revised rate coefficient for CCl₃O₂NO₂ thermal decay at about 1 atm total pressure (mainly N₂) is 1.42 × 10¹⁶ × exp(?11500/T) s^?1 from 268–298 K.     

Rate coefficient for the reaction OH + HO2 = H2O + O2 at 1 atmosphere pressure and 308 K

The rate coefficient for the reaction OH + HO₂ =H₂O + O₂ has been determined from measurements of the steady-state absorption of HO₂ at 210 nm, in low-frequency square-wave modulated photolysis of O₃ + H₂O mixtures. The value obtained was (9.9 ± 2.5) × 10^?11 cm³ molecule^?1 s^?1 at 308 K and 1 atm pressure.     

Kinetics of the gas-phase reactions of β-phellandrene with OH and NO3 radicals and O3 at 297 ± 2 K

Rate constants for the gas-phase reactions of the biogenically emitted monoterpene β-phellandrene with OH and NO₃ radicals and O₃ have been measured at 297 ± 2 K and atmospheric pressure of air using relative rate methods. The rate constants obtained were (in cm³ molecule^?1 s^?1 units): for reaction with the OH radical, (1.68 ± 0.41) × 10^?10; for reaction with the NO₃ radical, (7.96 ± 2.82) × 10^?12; and for reaction with O₃, (4.77 ± 1.23) × 10^?17, where the error limits include the estimated uncertainties in the reference reaction rate constants. Using these rate constants, the lifetime of β-phellandrene in the lower troposphere due to reaction with these species is calculated to be in the range of ca. 1–8 h, with the OH radical reaction being expected to dominate over the O₃ reaction as a loss process for β-phellandrene during daylight hours.     

Rate coefficients for the reactions of O(3P) with selected biogenic Hydrocarbons

The rate coefficients for the reaction of O(³P) with the biogenic hydrocarbons Δ³-carene, α-pinene, and isoprene have been measured using a direct method for the first time. O(³P) was generated from the pulsed photolysis of NO₂ or O₃ at 308 nm, and measured by resonance fluorescence at 131 nm. Rate coefficients at room temperature for the biogenics are similar: (3.4 ± 0.6) × 10^?11, (3.7 ± 0.6) × 10^?11, and (3.5 ± 0.6) × 10^?11 cm³ molec^?1 s^?1, for Δ³-carene, α-pinene, and isoprene, respectively. The rate coefficients for the reaction of O(³P) with NO₂ and ethene were also measured with the same method, and these values are within 4% and 10% of the currently recommended values, respectively. The correlation between OH and O(³P)-alkene reaction rate coefficients is updated and discussed. © 1995 John Wiley & Sons, Inc.     

Rate constants for the gas-phase reactions of cis-3-Hexen-1-ol,cis-3-Hexenylacetate,trans-2-Hexenal,and Linalool with OH and NO3 radicals and O3 at 296 ± 2 K,and OH radical formation yields from the O3 reactions

Rate constants for the gas-phase reactions of the four oxygenated biogenic organic compounds cis-3-hexen-1-ol, cis-3-hexenylacetate, trans-2-hexenal, and linalool with OH radicals, NO₃ radicals, and O₃ have been determined at 296 ± 2 K and atmospheric pressure of air using relative rate methods. The rate constants obtained were (in cm³ molecule^?1 s^?1 units): cis-3-hexen-1-ol: (1.08 ± 0.22) × 10^?10 for reaction with the OH radical; (2.72 ± 0.83) × 10^?13 for reaction with the NO₃ radical; and (6.4 ± 1.7) × 10^?17 for reaction with O₃; cis-3-hexenylacetate: (7.84 ± 1.64) × 10^?11 for reaction with the OH radical; (2.46 ± 0.75) × 10^?13 for reaction with the NO₃ radical; and (5.4 ± 1.4) × 10^?17 for reaction with O₃; trans-2-hexenal: (4.41 ± 0.94) × 10^?11 for reaction with the OH radical; (1.21 ± 0.44) × 10^?14 for reaction with the NO₃ radical; and (2.0 ± 1.0) × 10^?18 for reaction with O₃; and linalool: (1.59 ± 0.40) × 10^?10 for reaction with the OH radical; (1.12 ± 0.40) × 10^?11 for reaction with the NO₃ radical; and (4.3 ± 1.6) × 10^?16 for reaction with O₃. Combining these rate constants with estimated ambient tropospheric concentrations of OH radicals, NO₃ radicals, and O₃ results in calculated tropospheric lifetimes of these oxygenated organic compounds of a few hours. © 1995 John Wiley & Sons, Inc.     

Reaction of Amino Acids,Di‐ and Tripeptides with the Environmental Oxidant NO3.: A Laser Flash Photolysis and Computational Study

Absolute rate coefficients for the reaction between the important environmental free radical oxidant NO₃^. and a series of N‐ and C‐protected amino acids, di‐ and tripeptides were determined using 355 nm laser flash photolysis of cerium(IV) ammonium nitrate in the presence of the respective substrates in acetonitrile at 298±1 K. Through combination with computational studies it was revealed that the reaction with acyclic aliphatic amino acids proceeds through hydrogen abstraction from the α‐carbon, which is associated with a rate coefficient of about 1.8×10⁶ m ^?1 s^?1 per abstractable hydrogen atom. The considerably faster reaction with phenylalanine [k=(1.1±0.1)×10⁷ m ^?1 s^?1] is indicative for a mechanism involving electron transfer. An unprecedented amplification of the rate coefficient by a factor of 7–20 was found with di‐ and tripeptides that contain more than one phenylalanine residue. This suggests a synergistic effect between two aromatic rings in close vicinity, which makes such peptide sequences highly vulnerable to oxidative damage by this major environmental pollutant.     

FTIR study of the DMS/NO2/I2/N2 photolysis system: The reaction of IO radicals with DMS

A steady-state system involving the photolysis of NO₂ in an excess of I₂ as a source of IO radicals has been used to study the reaction IO + DMS in 760 Torr N₂ at 296 K. IO radicals were found to react rapidly with DMS, one molecule of DMSO being produced for each molecule of DMS consumed. Numerical analysis of the experimental results yielded a rate constant of (3.0 ± 1.5) × 10^?11 cm³ s^?1 for the reaction IO + DMS → DMSO + I.