Rate Coefficients of the Reactions of CN and NCO with O2 and NO2 at 296 K

The rate coefficients of the reactions of CN and NCO radicals with O₂ and NO₂ at 296 K: (1) CN + O₂ → products; (2) CN + NO₂ → products; (3) NCO + O₂ → products and (4) NCO + NO₂ → products have been measured with the laser photolysis-laser induced fluorescence technique. We obtained k₁ = (2.1 ± 0.3) × 10^?11 and k₂ = (7.2 ± 1.0) × 10^?11 cm³ molecule^?t s^?1 which agree well with published results. As no reaction was observed between NCO and O₂ at 297 K, an upper limit of k₃ < 4 × 10^?17 cm³ molecule^?1 S^?1 was estimated. The reaction of NCO with NO₂ has not been investigated previously. We measured k₄ = (2.2 ± 0.3) × 10^?11 cm³ molecule^?1 s^?1 at 296 K.     

Rate coefficients for the reaction of OH with HONO between 298 and 373 K

Rate coefficients, k₁, for the reaction OH + HONO → H₂O + NO₂, have been measured over the temperature range 298 to 373 K. The OH radicals were produced by 266 nm laser photolysis of O₃ in the presence of a large excess of H₂O vapor. The temporal profiles of OH were measured under pseudo-first-order conditions, in an excess of HONO, using time resolved laser induced fluorescence. The measured rate coefficient exhibits a slight negative temperature dependence, with k₁ = (2.8 ± 1.3) × 10^?12 exp((260 ± 140)/T) cm³ molecule^?1 s^?1. The measured values of k₁ are compared with previous determinations and the atmospheric implications of our findings are discussed.     

Rate constants of the reactions of OH radicals with cyclopropane and cyclobutane

The kinetics of the reactions of hydroxy radicals with cyclopropane and cyclobutane has been investigated in the temperature range of 298–492 K with laser flash photolysis/resonance fluorescence technique. The temperature dependence of the rate constants is given by k₁ = (1.17 ± 0.15) × 10^?16 T^3/2 exp[?(1037 ± 87) kcal mol^?1/RT] cm³ molecule^?1 s¹ and k₂ = (5.06 ± 0.57) × 10^?16 T^3/2 exp[?(228 ± 78) kcal mol^?1/RT] cm³ molecule^?1 s^?1 for the reactions OH + cyclopropane → products (1) and OH + cyclobutane → products (2), respectively. Kinetic data available for OH + cycloalkane reactions were analyzed in terms of structure-reactivity correlations involving kinetic and energetic parameters.     

Kinetic study of the gas‐phase reaction of the nitrate radical with methyl‐substituted thiophenes

The gas‐phase reactions of the NO₃ radical with 2‐methylthiophene, 3‐methylthiophene, and 2,5‐dimethylthiophene have been studied, using relative and absolute methods at 298 K. Determination of relative rate was performed using Teflon collapsible bag as the reaction chamber and gas chromatography as the analytical tool. For the absolute method, experiments were carried out using fast‐flow‐discharge technique with detection of NO₃ by laser‐induced fluorescence. The temperature dependence was studied by the absolute technique for the reactions of NO₃ with 2‐methylthiophene and 3‐methylthiophene in the range 263–335 K. The proposed Arrhenius expressions for the reaction of the nitrate radical with 2‐methylthiophene and 3‐methylthiophene are k = (4 ± 2) × 10^?16 exp[?(2200 ± 100)/T]] cm³ molecule^?1 s^?1 and k = (3 ± 2) × 10^?15 exp[?(1700 ± 200)/T]] cm³ molecule^?1 s^?1, respectively. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 286–293, 2003     

A kinetics study of the reaction of Cl with NO2

The third order rate coefficients for the addition reaction of Cl with NO₂, Cl + NO₂ + M → ClNO₂ (ClONO) + M; k₁, were measured to be k₁(He) = (7.5 ± 1.1) × 10^?31 cm⁶ molecule^?2 s^?1 and k₁(N₂) = (16.6 ± 3.0) × 10^?31 cm⁶ molecule^?2 s^?1 at 298 K using the flash photolysis-resonance fluorescence method. The pressure range of the study was 15 to 500 torr He and 19 to 200 torr N₂. The temperature dependence of the third order rate coefficients were also measured between 240 and 350 K. The 298 K results are compared with those from previous low pressure studies.     

The temperature dependence of the OH radical reactions with some aromatic compounds under simulated tropospheric conditions

The temperature dependence of the rate coefficients for the OH radical reactions with toluene, benzene, o-cresol, m-cresol, p-cresol, phenol, and benzaldehyde were measured by the competitive technique under simulated atmospheric conditions over the temperature range 258–373 K. The relative rate coefficients obtained were placed on an absolute basis using evaluated rate coefficients for the corresponding reference compounds. Based on the rate coefficient k(OH + 2,3-dimethylbutane) = 6.2 × 10^?12 cm³ molecule^?1s^?1, independent of temperature, the rate coefficient for toluene k_OH = 0.79 × 10^?12 exp[(614 ± 114)/T] cm³ molecule^?1 s^?1 over the temperature range 284–363 K was determined. The following rate coefficients in units of cm³ molecule^?1 s^?1 were determined relative to the rate coefficient k(OH + 1,3-butadiene) = 1.48 × 10^?11 exp(448/T) cm³ molecule^?1 s^?1: o-cresol; k_OH = 9.8 × 10^?13 exp[(1166 ± 248)/T]; 301–373 K; p-cresol; k_OH = 2.21 × 10^?12 exp[(943 ± 449)/T]; 301–373 K; and phenol, k_OH = 3.7 × 10^?13 exp[(1267 ± 233)/T]; 301–373 K. The rate coefficient for benzaldehyde k_OH = 5.32 × 10^?12 exp[(243 ± 85)/T], 294–343 K was determined relative to the rate coefficient k(OH + diethyl ether) = 7.3 × 10^?12 exp(158/T) cm³ molecule^?1 s^?1. The data have been compared to the available literature data and where possible evaluated rate coefficients have been deduced or updated. Using the evaluated rate coefficient k(OH + toluene) = 1.59 × 10^?12 exp[(396 ± 105)/T] cm³ molecule^?1 s^?1, 213–363 K, the following rate coefficient for benzene has been determined k_OH = 2.58 × 10^?12 exp[(?231 ± 84)/T] cm³ molecule^?1 s^?1 over the temperature range 274–363 K and the rate coefficent for m-cresol, k_OH = 5.17 × 10^?12 exp[(686 ± 231)/T] cm³ molecule^?1 s^?1, 299–373 K was determined relative to the evaluated rate coefficient k(OH + o-cresol) = 2.1 × 10^?12 exp[(881 ± 356)/T] cm³ molecule^?1 s^?1. The tropospheric lifetimes of the aromatic compounds studied were calculated relative to that for 1,1,1-triclorethane = 6.3 years at 277 K. The lifetimes range from 6 h for m-cresol to 15.5 days for benzene. © 1995 John Wiley & Sons, Inc.     

Absolute Rate constants for O + No + N2 → NO2 + N2 from 217–500 K

Flash photolysis of NO coupled with time resolved detection of O via resonance fluorescence has been used to obtain rate constants for the reaction O + NO + N₂ → NO₂ + N₂ at temperatures from 217 to 500 K. The measured rate constants obey the Arrhenius equation k = (15.5 ± 2.0) × 10^?33 exp(1160 ± 70)/1.987 T] cm⁶ molecule^?2 s^?1. An equally acceptable equation describing the temperature dependence of k is k = 3.80 × 10^?27/T^1.82 cm⁶ molecule^?2 s^?1. These results are discussed and compared with previous work.     

Kinetic study of the reaction of OH with HCl from 240–1055 K

Absolute rate coefficients for the reaction of OH with HCl (k₁) have been measured as a function of temperature over the range 240–1055 K. OH was produced by flash photolysis of H₂O at λ > 165 nm, 266 nm laser photolysis of O₃/H₂O mixtures, or 266 nm laser photolysis of H₂O₂. OH was monitored by time-resolved resonance fluorescenceor pulsed laser–induced fluorescence. In many experiments the HCl concentration was measured in situ in the slow flow reactor by UV photometry. Over the temperature range 240–363 K the following Arrhenius expression is an adequate representation of the data: k₁ = (2.4 ± 0.2) × 10^?12 exp[?(327 ± 28)/T]cm³ molecule^?1 s^?1. Over the wider temperature range 240–1055 K, the temperature dependence of k₁ deviates from the Arrhenius form, but is adequately described by the expression k₁ = 4.5 × 10^?17 T^1.65 exp(112/T) cm³ molecule^?1 s^?1. The error in a calculated rate coefficient at any temperature is 20%.     

Kinetics of HCCl + NOx reactions

The kinetics of reactions of HCCl with NO and NO₂ were investigated over the temperature ranges 298–572 k and 298–476 k, respectively, using laser‐induced fluorescence spectroscopy to measure total rate constants and time‐resolved infrared diode laser absorption spectroscopy to probe reaction products. Both reactions are fast, with k(HCCl + NO) = (2.75 ± 0.2) × 10^?11 cm³ molecule^?1 s^?1 and k(HCCl + NO₂) = (1.10 ± 0.2) × 10^?10 cm³ molecule^?1 s^?1 at 296 K. Both rate constants displayed only a slight temperature dependence. Detection of products in the HCCl + NO reaction at 296 K indicates that HCNO + Cl is the major product with a branching ratio of ? = 0.68 ± 0.06, and NCO + HCl is a minor channel with ? = 0.24 ± 0.04. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 34: 12–17, 2002     

Ab initio chemical kinetics for the NH2 + HNOx reactions,part III: Kinetics and mechanism for NH2 + HONO2

The kinetics and mechanism for the reaction of NH₂ with HONO₂ have been investigated by ab initio calculations with rate constant prediction. The potential energy surface of this reaction has been computed by single‐point calculations at the CCSD(T)/6‐311+G(3df, 2p) level based on geometries optimized at the B3LYP/6‐311+G(3df, 2p) level. The reaction producing the primary products, NH₃ + NO₃, takes place via a precursor complex, H₂N…HONO₂ with an 8.4‐kcal/mol binding energy. The rate constants for major product channels in the temperature range 200–3000 K are predicted by variational transition state or variational Rice–Ramsperger–Kassel–Marcus theory. The results show that the reaction has a noticeable pressure dependence at T < 900 K. The total rate constants at 760 Torr Ar‐pressure can be represented by k_total = 1.71 × 10^?3 × T^?3.85 exp(?96/T) cm³ molecule^?1 s^?1 at T = 200–550 K, 5.11 × 10^?23 × T^+3.22 exp(70/T) cm³ molecule^?1 s^?1 at T = 550–3000 K. The branching ratios of primary channels at 760 Torr Ar‐pressure are predicted: k₁ producing NH₃ + NO₃ accounts for 1.00–0.99 in the temperature range of 200–3000 K and k₂ + k₃ producing H₂NO + HONO accounts for less than 0.01 when temperature is more than 2600 K. The reverse reaction, NH₃ + NO₃ → NH₂ + HONO₂ shows relatively weak pressure dependence at P < 100 Torr and T < 600 K due to its precursor complex, NH₃…O₃N with a lower binding energy of 1.8 kcal/mol. The predicted rate constants can be represented by k_?1 = 6.70 × 10^?24 × T^+3.58 exp(?850/T) cm³ molecule^?1 s^?1 at T = 200–3000 K and 760 Torr N₂ pressure, where the predicted rate at T = 298 K, 2.8 × 10^?16 cm³ molecule^?1 s^?1 is in good agreement with the experimental data. The NH₃ + NO₃ formation rate constant was found to be a factor of 4 smaller than that of the reaction OH + HONO₂ producing the H₂O + NO₃ because of the lower barrier for the transition state for the OH + HONO₂. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 42: 69–78, 2010     

Temperature dependence of the reaction NO + NO3 → 2NO2

The flash photolysis-visible absorption technique has been used to measure rate constants for the reaction NO + NO₃ → 2NO₂ (1) over the temperature range 224–328 K. The temperature dependence of the rate constant is given by the expression k₁(T) = (1.59 ± 0.32) × 10⁻¹¹exp(122/T) cm³ molecule⁻¹ s⁻¹ where the stated uncertainties refer to the ± 2σ limits from both random and systematic errors.     

Rate constants for the reactions of conjugated olefins with NO2 in the gas phase

Gas-phase rate constants for the reaction of NO₂ with 16 conjugated olefins were determined at room temperature by either conventional methods for bimolecular processes or by competitive reactions. It was found that the rate constants for conjugated olefins were larger than those for simple mono-olefins by factors of 10³–10⁴. Temperature dependence studies reveal that the difference in the rate constants for the two types of reactions can primarily be attributed to differences in their activation energies: k_{1,3-cyclohexadiene} = 5.8 × 10^?14 exp[?(6.1 ± 1.6)/RT] cm³ molecule^?1 s^?1; k_cis-2-butene = 4.68 × 10^?14 exp(?11.2/RT) cm³ molecule^?1 s^?1 [2]. A linear free energy relationship between the reactions of OH and NO₂ with conjugated diolefins was observed.     

Ab initio chemical kinetics for the NH2 + HNOx reactions,part II: Kinetics and mechanism for NH2 + HONO

The kinetics and mechanism for the reaction of NH₂ with HONO have been investigated by ab initio calculations with rate constant prediction. The potential energy surface of this reaction has been computed by single‐point calculations at the CCSD(T)/6‐311+G(3df, 2p) level based on geometries optimized at the CCSD/6‐311++G(d, p) level. The reaction producing the primary products, NH₃ + NO₂, takes place via precomplexes, H₂N???c‐HONO or H₂N???t‐HONO with binding energies, 5.0 or 5.9 kcal/mol, respectively. The rate constants for the major reaction channels in the temperature range of 300–3000 K are predicted by variational transition state theory or Rice–Ramsperger–Kassel–Marcus theory depending on the mechanism involved. The total rate constant can be represented by k_total = 1.69 × 10^?20 × T^2.34 exp(1612/T) cm³ molecule^?1 s^?1 at T = 300–650 K and 8.04 × 10^?22 × T^3.36 exp(2303/T) cm³ molecule^?1 s^?1 at T = 650–3000 K. The branching ratios of the major channels are predicted: k₁ + k₃ producing NH₃ + NO₂ accounts for 1.00–0.98 in the temperature range 300–3000 K and k₂ producing OH + H₂NNO accounts for 0.02 at T > 2500 K. The predicted rate constant for the reverse reaction, NH₃ + NO₂ → NH₂ + HONO represented by 8.00 × 10^?26 × T^4.25 exp(?11,560/T) cm³ molecule^?1 s^?1, is in good agreement with the experimental data. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 678–688, 2009     

Rate constants of the reactions of O(3P) atoms with Br2 and NO2 over the temperature range 220-950 K

The kinetics of the reactions of Br₂ and NO₂ with ground state oxygen atoms have been studied over a wide temperature range, T = 220-950 K, using a low-pressure flow tube reactor coupled with a quadrupole mass spectrometer: O + NO₂ → NO + O₂ (1) and O + Br₂ → Br + BrO (2). The rate constant of reaction (1) was determined under pseudo–first-order conditions, either monitoring the kinetics of O-atom or NO₂ consumption in excess of NO₂ or of the oxygen atoms, respectively: k₁ = (6.1 ± 0.4) × 10⁻¹² exp((155 ± 18)/T) cm³ molecule⁻¹ s⁻¹ (where the uncertainties represent precision at the 2σ level, the estimated total uncertainty on k₁ being 15% at all temperatures). The temperature dependence of k₁, found to be in excellent agreement with multiple previous low-temperature data, was extended to 950 K. The rate constant of reaction (2) determined under pseudo–first-order conditions, monitoring the kinetics of Br₂ consumption in excess of O-atoms, showed upward curvature at low and high temperatures of the study and was fitted with the following three-parameter expression: k₂ = 9.85 × 10⁻¹⁶ T^1.41 exp(543/T) cm³ molecule⁻¹ s⁻¹ at T = (220-950) K, which is recommended from the present study with an independent of temperature conservative uncertainty of 15% on k₂.     

Temperature dependence of the rate constant for the reaction OH + H2S in He,N2, and O2

The rate constants of the reaction between OH and H₂S in He, N₂, and O₂ over the temperature range 245–450 K have been determined using the discharge flow-resonance fluorescence technique. At 299 K, k₁ = (4.4 ± 0.7) × 10^?12 cm³ molecule^?1 s^?1. The temperature dependence of the rate constant can be fitted either by k₁ = 5.6 × 10^?12 exp(?57/T) or by k₁ = (3.8 × 10^?19)T^2.43 exp(732/T) to within 8 and 9%, respectively. However, the non-Arrhenius behavior can be confidently confirmed. The absence of the pressure dependence and the third-body effect at low temperature suggest that the complex formation mechanism is not important over the temperature range of our study.     

Reaction of the NO3 radical with some thiophenes: Kinetic study and a correlation between rate constant and EHOMO

The rate constants and activation energies for the reactions of some thiophenes with the NO₃ radical were measured using the absolute fast‐flow discharge technique at 263–335 K and low pressure. The proposed Arrhenius expressions for 2‐ethylthiophene, 2‐propylthiophene, 2,5‐dimethylthiophene, and 2‐chlorothiophene are k = (4.2 ± 0.28) ×10^?16 exp[(2280 ± 70)]/T, k = (7.0 ± 2) × 10^?18 exp[(3530 ± 70)]/T, k = (1 ± 1) × 10^?14 exp[(1648 ± 240)]/T, and k = (8 ± 2) × 10^?17 exp[(2000 ± 200)]/T (k = cm³ molecule^?1 s^?1), respectively. The reactions of this radical with 2‐chlorothiophene and 3‐chlorothiophene were also studied by a relative method in a Teflon static reactor at room temperature and atmospheric pressure. The effect of substitution on thiophene reactivity is discussed, and a relationship between the rate constants and the ionization potential (IP = ?E_HOMO) has been proposed. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 570–576, 2006     

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.     

Kinetics of the gas‐phase reactions of CHXCFX (X = H,F) with OH (253–328 K) and NO3 (298 K) radicals and O3 (236–308 K)

Rate constants for the reactions of OH and NO₃ radicals with CH₂?CHF (k₁ and k₄), CH₂?CF₂ (k₂ and k₅), and CHF?CF₂ (k₃ and k₆) were determined by means of a relative rate method. The rate constants for OH radical reactions at 253–328 K were k₁ = (1.20 ± 0.37) × 10^?12 exp[(410 ± 90)/T], k₂ = (1.51 ± 0.37) × 10^?12 exp[(190 ± 70)/T], and k₃ = (2.53 ± 0.60) × 10^?12 exp[(340 ± 70)/T] cm³ molecule^?1 s^?1. The rate constants for NO₃ radical reactions at 298 K were k₄ = (1.78 ± 0.12) × 10^?16 (CH₂?CHF), k₅ = (1.23 ± 0.02) × 10^?16 (CH₂?CF₂), and k₆ = (1.86 ± 0.09) × 10^?16 (CHF?CF₂) cm³ molecule^?1 s^?1. The rate constants for O₃ reactions with CH₂?CHF (k₇), CH₂?CF₂ (k₈), and CHF?CF₂ (k₉) were determined by means of an absolute rate method: k₇ = (1.52 ± 0.22) × 10^?15 exp[?(2280 ± 40)/T], k₈ = (4.91 ± 2.30) × 10^?16 exp[?(3360 ± 130)/T], and k₉ = (5.70 ± 4.04) × 10^?16 exp[?(2580 ± 200)/T] cm³ molecule^?1 s^?1 at 236–308 K. The errors reported are ±2 standard deviations and represent precision only. The tropospheric lifetimes of CH₂?CHF, CH₂?CF₂, and CHF?CF₂ with respect to reaction with OH radicals, NO₃ radicals, and O₃ were calculated to be 2.3, 4.4, and 1.6 days, respectively. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 619–628, 2010     

Ketone photolysis in the presence of oxygen: A useful source of OH for flash photolysis kinetics experiments

Previous studies have shown a significant OH yield from the reaction of RCO radicals (generated from the photolysis of corresponding ketone) with oxygen below total pressures of 200 Torr. The potential of these reactions as a source of OH radicals for flash photolytic kinetic studies is investigated. The viability of the method was tested by measuring rate coefficients for the reaction of OH with ethanol using both acetone/O₂ mixtures and t‐butyl hydroperoxide photolysis. The results (with statistical errors at the 2σ level) are in excellent agreement with each other (k_EtOH(acetone) = (5.87 ± 0.34) × 10^?18 T² exp((515 ± 21)K/T) cm³ molecule^?1 s^?1 and k_EtOH (t‐butyl hydroperoxide) = (5.27 ± 0.34) × 10^?18 T² exp((557 ± 20)K/T) cm³ molecule^?1 s^?1) and with the IUPAC recommendation. The reaction of OH with methyl ethyl ketone (2‐butanone) has also been investigated using a similar technique. The results show a strong non‐Arrhenius temperature dependence, k = (3.84 ± 0.12) × 10^?24× T⁴ × exp((1038 ± 11)/t). The merits of the ketone/oxygen OH source are contrasted with other established precursors. A major advantage of the technique is the ability to cleanly generate OD without the potential for isotopic scrambling prior to photolysis. © 2008 Wiley Periodicals, Inc. 40: 504–514, 2008     

The temperature dependence of the bimolecular channels of the ClO + ClO reaction over the range T = 298–323 K

The bimolecular channels of the ClO self‐reaction, although negligible under stratospheric conditions, become significant above ambient temperature. The kinetics of two of the three bimolecular channels of the ClO self‐reaction, ClO + ClO → Cl₂ + O₂ (1b) and ClO + ClO → OClO + Cl (1d), were studied at T = 298–323 K and at ambient pressure (p_atm≈ 760 ± 10 Torr). Radicals were generated via laser photolysis and monitored using UV absorption spectroscopy. The inclusion of charge‐coupled device (CCD) detection allowed broadband monitoring of the radicals of interest along with the temporal resolution of their concentrations. Accurate and unequivocal quantification of the structured absorbers (ClO and OClO) was obtained via differential fitting procedures. The Arrhenius expressions obtained are k_1b = 2.9_?1.8^+4.4 × 10^?14exp[?(283 ± 282)/T] cm³ molecule^?1 s^?1 and k_1d = 7.2_?6.1⁺³⁹ × 10^?15exp[?(225 ± 574)/T] cm³ molecule^?1 s^?1, where the errors are 1σ. The temperature dependences obtained in this work for both channels monitored are considerably less pronounced than those reported by Nickolaisen et al. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 386–397, 2012