Rate coefficients for the gas‐phase reactions of OH radicals with methylbutenols at 298 K

The relative‐rate method has been used to determine the rate coefficients for the reactions of OH radicals with three C₅ biogenic alcohols, 2‐methyl‐3‐buten‐2‐ol (k₁), 3‐methyl‐3‐buten‐1‐ol (k₂), and 3‐methyl‐2‐buten‐1‐ol (k₃), in the gas phase. OH radicals were produced by the photolysis of CH₃ONO in the presence of NO. Di‐n‐butyl ether and propene were used as the reference compounds. The absolute rate coefficients obtained with the two reference compounds agreed well with each other. The O₃ and O‐atom reactions with the target alcohols were confirmed to have a negligible contribution to their total losses by using two kinds of light sources with different relative rates of CH₃ONO and NO₂ photolysis. The absolute rate coefficients were obtained as the weighted mean values for the two reference compound systems and were k₁ = (6.6 ± 0.5) × 10^?11, k₂ = (9.7 ± 0.7) × 10^?11, and k₃ = (1.5 ± 0.1) × 10^?10 cm³ molecule^?1 s^?1 at 298 ± 2 K and 760 torr of air. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 379–385 2004     

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.     

Site-specific rate coefficients for reaction of OH with ethanol from 298 to 900 K

The rate coefficients for reactions of OH with ethanol and partially deuterated ethanols have been measured by laser flash photolysis/laser-induced fluorescence over the temperature range 298-523 K and 5-100 Torr of helium bath gas. The rate coefficient, k(1.1), for reaction of OH with C(2)H(5)OH is given by the expression k(1.1) = 1.06 × 10(-22)T(3.58)?exp(1126/T) cm(3) molecule(-1) s(-1), and the values are in good agreement with previous literature. Site-specific rate coefficients were determined from the measured kinetic isotope effects. Over the temperature region 298-523 K abstraction from the hydroxyl site is a minor channel. The reaction is dominated by abstraction of the α hydrogens (92 ± 8)% at 298 K decreasing to (76 ± 9)% with the balance being abstraction at the β position where the errors are 2σ. At higher temperatures decomposition of the CH(2)CH(2)OH product from β abstraction complicates the kinetics. From 575 to 650 K, biexponential decays were observed, allowing estimates to be made for k(1.1) and the fractional production of CH(2)CH(2)OH. Above 650 K, decomposition of the CH(2)CH(2)OH product was fast on the time scale of the measured kinetics and removal of OH corresponds to reaction at the α and OH sites. The kinetics agree (within ±20%) with previous measurements. Evidence suggests that reaction at the OH site is significant at our higher temperatures: 47-53% at 865 K.     

Rate constants for the reaction of Cl atoms with O3 at temperatures from 298 to 184 K

Using the standard, low pressure, discharge‐flow technique, with resonance fluorescence in the vacuum ultraviolet to observe Cl atoms, rate constants have been determined for the reaction of Cl atoms with O₃ at temperatures down to 184 K. The measured rate constants for 298–184 K fit the Arrhenius expression k(T) = (3.1 ± 1.3₅) × 10^?11 exp((?280 ±100 K)/T) cm³ molecule^?1 s^?1. The results extend the data on this key atmospheric reaction to slightly lower temperatures. The data are in fairly good agreement with those currently in the literature but suggest that the rate constant is approximately 15% lower than that given by currently recommended rate expressions at the lowest temperatures found in the stratosphere.© 2001 John Wiley & Sons, Inc. Int J Chem Kinet 34: 104–109, 2002     

Rate coefficients for the reactions of OH radicals with Methylglyoxal and Acetaldehyde

Rate coefficients have been measured for the reaction of OH radicals with methylglyoxal from 260 to 333 K using the discharge flow technique and laser-induced fluorescence detection of OH. The rate coefficient was found to be (1.32±0.30) × 10^?11 cm³ molecule^?1 s^?1 at room temperature, with a distinct negative temperature dependence (E/R of ?830 ± 300 K). These are the first measurements of the temperature dependence of this reaction. The reaction of OH with acetaldehyde was also investigated, and a rate coefficient of (1.45 ± 0.25) × 10^?11 cm³ molecule^?1 s^?1 was found at room temperature, in accord with recent studies. Experiments in which O₂ was added to the flow showed regeneration of OH following the reaction of CH₃CO radicals with O₂. However, chamber experiments at atmospheric pressure using FTIR detection showed no evidence for OH production. FTIR experiments have also been used to investigate the chemistry of the CH₃COCO radical formed by hydrogen abstraction from methylglyoxal. © 1995 John Wiley & Sons, Inc.     

Rate constants for the gas-phase reactions of OH radicals and Cl atoms with n-alkyl nitrites at atmospheric pressure and 298 K

Rate constants for the reactions of OH radicals and Cl atoms with CH₃ONO, C₂H₅ONO, n-C₃H₇ONO, n-C₄H₉ONO, and n-C₅H₁₁ONO have been determined at 298 ± 2 K and a total pressure of approximately 1 atm. The OH rate data were obtained using both the absolute rate technique of pulse radiolysis combined with kinetic spectroscopy and a relative rate method involving simultaneous measurement of the loss of the nitrite and the reference compound. The Cl rate constants were measured using the relative rate method. Values of the rate constants in units of 10^?13 cm³ molecule^?1 s^?1 are:

Rate coefficients and products for gas‐phase reactions of chlorine atoms with cyclic unsaturated hydrocarbons at 298 K

Rate coefficients for the reaction of Cl atoms with cycloalkenes have been determined using the relative rate method, at 298 K and atmospheric pressure of N₂. Reference molecule was n‐hexane, and the concentrations of the organics were followed by gas chromatographic analysis. Cl atoms were prepared by photolysis of trichloroacetyl chloride at 254 nm. The relative rates of reactions of Cl atoms with cycloalkenes, with respect to n‐hexane, are measured as 1.12 ± 0.38, 1.31 ± 0.14, and 1.69 ± 0.18 for cyclopentene, cyclohexene, and cycloheptene, respectively. Considering the absolute value of the rate coefficient of the reaction of Cl atom with n‐hexane as 3.03 ± 0.06 × 10^?10 cm³ molecule^?1 s^?1, the rate coefficient values for cyclopentene, cyclohexene, and cycloheptene are calculated to be (3.39 ± 1.08) × 10^?10, (3.97 ± 0.43) × 10^?10, and (5.12 ± 0.55) × 10^?10 cm³ molecule^?1 s^?1, respectively. The experiments for each molecule were repeated six to eight times, and the slopes and the rate coefficients given above are the average values of these measurements, and the quoted error includes 2σ as well as all other uncertainties in the measurement and calculations. The rate coefficient increases linearly with the number of carbon atoms, with an increment per additional CH₂ group being (8.7 ± 1.6) × 10^?12 cm³ molecule^?1 s^?1. Chloroketones and chloroalcohols, along with unsaturated ketones and alcohols, were found to be the major products of Cl‐atom‐initiated oxidation of cycloalkenes in the presence of air. The atmospheric implications of these results are discussed, along with a comparison with the reported structure activity relationships. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 42: 98–105, 2010     

Rate coefficients for the reactions of OH with n‐propanol and iso‐propanol between 237 and 376 K

The rate coefficients for the reaction OH + CH₃CH₂CH₂OH → products (k₁) and OH + CH₃CH(OH)CH₃ → products (k₂) were measured by the pulsed‐laser photolysis–laser‐induced fluorescence technique between 237 and 376 K. Arrhenius expressions for k₁ and k₂ are as follows: k₁ = (6.2 ± 0.8) × 10^?12 exp[?(10 ± 30)/T] cm³ molecule^?1 s^?1, with k₁(298 K) = (5.90 ± 0.56) × 10^?12 cm³ molecule^?1 s^?1, and k₂ = (3.2 ± 0.3) × 10^?12 exp[(150 ± 20)/T] cm³ molecule^?1 s^?1, with k₂(298) = (5.22 ± 0.46) × 10^?12 cm³ molecule^?1 s^?1. The quoted uncertainties are at the 95% confidence level and include estimated systematic errors. The results are compared with those from previous measurements and rate coefficient expressions for atmospheric modeling are recommended. The absorption cross sections for n‐propanol and iso‐propanol at 184.9 nm were measured to be (8.89 ± 0.44) × 10^?19 and (1.90 ± 0.10) × 10^?18 cm² molecule^?1, respectively. The atmospheric implications of the degradation of n‐propanol and iso‐propanol are discussed. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 42: 10–24, 2010     

Study of the reactions of OH with HCl,HBr, and HI between 298 K and 460 K

The reactions between OH radicals and hydrogen halides (HCl, HBr, HI) have been studied between 298 and 460 K by using a discharge flow-electron paramagnetic resonance technique. The rate constants were found to be k_HCl(298 K) = (7.9 ± 1.3) × 10⁻¹³ cm³ molecule⁻¹ s⁻¹ with a weak positive temperature dependence, k_HBr (298-460 K) = (1.04 ± 0.2) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹, and k_HI(298 K) = (3.0 ± 0.3) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹, respectively. The homogeneous nature of these reactions has been experimentally tested.     

Kinetic isotope effects and rate constants for the gas‐phase reactions of three deuterated toluenes with OH from 298 to 353 K

The rate constants for the gas‐phase reactions of three deuterated toluenes with hydroxyl radicals were measured using the relative rate technique over the temperature range 298–353 K at about 1 atm total pressure. The OH radicals were generated by photolysis of H₂O₂, and helium was used as the diluent gas. The disappearance of reactants was followed by online mass spectrometry, which resulted in high time resolution, allowing for a large amount of data to be collected and used in the determination of the Arrhenius parameters. The following Arrhenius expressions have been determined for these reactions (in units of cm³ molecule^?1 s^?1): k=(6.42_?0.99^+1.17)×10^?13exp [(661±54)/T] for toluene‐d₃, k=(2.11_?0.69^+1.03)×10^?12exp [(287±128)/T]for toluene‐d₅, and k=(1.40^+0.44_?0.33)×10^?12exp [(404±88)/T]for toluene‐d₈. The kinetic isotope effects (KIEs, k_H/k_D) of these reactions were 1.003 ± 0.042 for all three compounds at 298 K. The KIE for toluene‐d₃ was temperature dependent; at 350 K, its KIE was 1.122^+0.048_?0.046. The KIE of toluene‐d₅ and toluene‐d₈ did not vary significantly with temperature. These KIE results suggest that methyl H‐atom abstraction is more important than aromatic OH addition at higher temperatures. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 821–827, 2012     

Rate coefficients for the reaction of OH with Cl2, Br2, and I2 from 235 to 354 K

Rate coefficients for the reaction of OH with Cl₂, (k₁), Br₂, (k₂) and I₂, (k₃), were measured under pseudo‐first‐order conditions in OH. OH was produced by pulsed laser photolysis of H₂O₂ (or HNO₃) and its temporal profile was monitored by laser‐induced fluorescence. The measured rate coefficients for k₁ (231–354 K) and k₂ (235–357 K) are: k₁ (T) = (3.77 ± 1.02) × 10⁻¹² exp[−(1228 ± 140)/T] cm³ molecule⁻¹ s⁻¹ k₂ (T) = (1.98 ± 0.51) × 10⁻¹¹ exp[(238 ± 70)/T] cm³ molecule⁻¹ s⁻¹ k₃ was independent of temperature between 240 and 348 K with an average value of (2.10 ± 0.60) × 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹. The quoted uncertainties are 2σ (95% confidence limits, 1σ_A = Aσ_lnA) and include estimated systematic errors. Our measurements significantly im‐prove the accuracy of k₁. This is the first report of a slight negative temperature dependence for k₂ and of the temperature independence of k₃. © 1999 John Wiley & Sons, Inc.* Int J Chem Kinet 31: 417–424, 1999     

Rate coefficients for the OH + CFH2CH2OH reaction between 238 and 355 K

The rate coefficient for the reaction OH + CFH2CH2OH --> products (k1) between 238 and 355 K was measured using the pulsed laser photolysis-laser induced fluorescence (PLP-LIF) technique to be (5.15 +/- 0.88)x 10(-12) exp[-(330 +/- 45)/T] cm3 molecule(-1) s(-1); k1(298 K)= 1.70 x 10(-12) cm3 molecule(-1) s(-1). The quoted uncertainties are 2sigma(95% confidence level) and include estimated systematic errors. The present results are discussed in relation to the measured rate coefficients for the reaction of OH with other fluorinated alcohols and those calculated using recently reported structure additivity relationships for fluorinated compounds (K. Tokuhashi, H. Nagai, A. Takahashi, M. Kaise, S. Kondo, A. Sekiya, M. Takahashi, Y. Gotoh and A. Suga, J. Phys. Chem. A, 1999, 103, 2664-2672, ). Infrared absorption cross sections for CFH2CH2OH are reported and they are used to calculate the global warming potentials (GWP) for CFH2CH2OH of approximately 8, approximately 2, and approximately 1, respectively, for the 20, 100 and 500 year horizons. A brief discussion of the atmospheric degradation of CFH2CH2OH is provided. It is concluded that CFH2CH2OH is an acceptable substitute for CFCs in terms of its impact on Earth's climate and the composition of the atmosphere. The room temperature rate coefficient for the reaction OH + CFH2CH2OH --> products (k10) was measured to be 3.26 x 10(-12) cm3 molecule(-1) s(-1), in good agreement with recent measurements from this laboratory.     

Rate coefficients for the reaction of OH with a series of unsaturated alcohols between 263 and 371 K

Rate coefficients for the gas-phase reactions of OH radicals with four unsaturated alcohols, 3-methyl-3-buten-1-ol (k1), 2-buten-1-ol (k2), 2-methyl-2-propen-1-ol (k3) and 3-buten-1-ol (k4), were measured using two different techniques, a conventional relative rate method and the pulsed laser photolysis-laser induced fluorescence technique. The Arrhenius rate coefficients (in units of cm(3) molecule(-1) s(-1)) over the temperature range 263-371 K were determined from the kinetic data obtained as k1 = (5.5 +/- 1.0) x 10(-12) exp [(836 +/- 54)/T]; k2 = (6.9 +/- 0.9) x 10(-12) exp [(744 +/- 40)/T]; k3 = (10 +/- 1) x 10(-12) exp [(652 +/- 27)/T]; and k4 = (4.0 +/- 0.4) x 10(-12) exp [(783 +/- 32)/T]. At 298 K, the rate coefficients obtained by the two methods for each of the alcohols studied were in good agreement. The results are presented and compared with those obtained previously for the same and related reactions of OH radicals. Reactivity factors for substituent groups containing the hydroxyl group are determined. The atmospheric implications for the studied alcohols are considered briefly.     

Rate coefficients for the gas-phase reactions of bromine radicals with a series of alkenes,dienes, and aromatic hydrocarbons at 298 ± 2 K

Using the relative kinetic method rate coefficients have been determined for the gas-phase reaction of bromine (Br) radicals with a series of alkenes, chloroalkenes, dienes, and aromatic hydrocarbons in 1000 mbar of synthetic air at 298 ± 2 K. Both the UV photolysis of CH₂Br₂ (λ = 254 nm) and the visible photolysis of Br₂ (320 ≤ λ ≤ 480) were used to generate Br radicals. For the alkenes and dienes the following rate coefficients were obtained (in units of 10⁻¹² cm³ molecule⁻¹ s⁻¹): trans-2-butene 9.26 ± 1.85; 2-methyl-1-butene 15.20 ± 3.00; 2-methyl-2-butene 19.10 ± 3.80; 2,3-dimethyl-2-butene 28.20 ± 5.60; α-pinene 22.20 ± 4.40. β-pinene 28.60 ± 5.70; 1,3-butadiene 57.50 ± 11.50; isoprene 74.20 ± 14.80; and 2,3-dimethyl-1,3-butadiene 81.7 ± 16.30. For the chloroalkenes and aromatic hydrocarbons the following rate coefficients were obtained (in units of 10⁻¹³ cm³ molecule⁻¹ s⁻¹): chloroethene 7.37 ± 1.92; 1,1-dichloroethene 3.66 ± 0.73; trichloroethene 0.90 ± 0.18; tetrachloroethene ≤ 0.1; benzene ≤ 0.10; toluene ≤ 0.10; p-xylene ≤ 0.10; and furan ≤ 0.10. With the exception of trans-2-butene, this study represents the first determination of the rate coefficients for all of the compounds. © 1996 John Wiley & Sons, Inc.     

Rate coefficients for CS reactions with O2, O3 and NO2 AT 298 K

CS radicals have been produced by photodissociation of CS₂ at 193 nm and their disappearance monitored by LIF. The vibrationally excited CS radicals rapidly relax to CS(ν = 0). At 298 K, the rate coefficients for CS(ν = 0) reactions with O₂, O₃ and NO₂ are (2.9 ± 0.4) × 10_?19, (3.0 ± 0.4) × 10^?16 and (7.6 ± 1.1) × 10^?17 cm³ molecule^?1 s^?1 respectively. The quenching of CS(A ¹II)_ν=0 by He has a rate coefficient of (1.3 ± 0.2) × 10^?12 cm³ molecule^?1 s^?1.     

Rate constants for the reactions of molecular iodine with Cl,SiCl3, and SiH3 at 298 K

Rate constants k₁, k₂, and k₃ have been measured at 298 K by means of a laser photolysis-laser magnetic resonance technique and (or) by a laser photolysis-infrared chemiluminescence detection technique (LMR and IRCL, respectively). \hfill\hbox to 12em{$\rm Cl+I_2\longrightarrow ICl+I;$}\hbox to 8em{$\rm {\it k}_1=(2.5\pm 0.7)\times 10^{-10}(IRCL)$}\hfill(1)\\\hfill\hbox to 12em{}\hbox to 8em{$\rm {\it k}_1=(2.8\pm 0.8)\times 10^{-10}(LMR)$}\hfill \\\hfill\hbox to 12em{$\rm SiCl_3+I_2\longrightarrow SiCl_3I+I;$}\hbox to 8em{$\rm {\it k}_2=(5.8\pm 1.8)\times 10^{-10}(IRCL)$}\hfill (2)\\\hfill\hbox to 12em{$\rm SiH_3+I_2\longrightarrow SiIH_3+I;$}\hbox to 8em{$\rm {\it k}_3=(1.8\pm 0.46)\times 10^{-10}(LMR)$}\hfill (3)\\ As an average of the LMR and IRCL results we offer the value k₁ = (2.7 ± 0.6) × 10⁻¹⁰. Units are cm³ molecule⁻¹ s⁻¹; uncertainties are 2σ including precision and estimated systematic errors. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 25–33, 1997.     

Rate coefficients for the reactions CH3 + Br2 (224–358 K), CH3CO + Br2 (228 and 298 K), and Cl + Br2 (228 and 298 K)

Rate coefficients for the reactions of CH₃ + Br₂ (k₂), CH₃CO + Br₂ (k₃), and Cl + Br₂ (k₅) were measured using the laser‐pulsed photolysis method combined with detection of the product Br atoms using resonance fluorescence. For the reactions involving organic radicals, the rate coefficients were observed to increase with decreasing temperature and within the temperature range explored, were adequately described by Arrhenius‐like expressions: k₂ (224–358 K) = 1.83 × 10^?11 exp(252/T) and k₃ (228–298 K) = 2.92 × 10^?11 exp(361/T) cm³ molecule^?1 s^?1. The total, temperature‐independent uncertainty for each reaction (including possible systematic errors in Br₂ concentration measurement) was estimated as ～7% for k₂ and 10% for k₃. Accurate data on k₅ was obtained at 298 K, with a value of 1.88 × 10^?10 cm³ molecule^?1 s^?1 obtained (with an associated error of 6%). A limited data set at 228 K suggests that k₅ is, within experimental uncertainty, independent of temperature. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 575–585, 2010