Rate coefficients for the OH + acetaldehyde (CH3CHO) reaction between 204 and 373 K

The rate coefficient, k₁, for the gas‐phase reaction OH + CH₃CHO (acetaldehyde) → products, was measured over the temperature range 204–373 K using pulsed laser photolytic production of OH coupled with its detection via laser‐induced fluorescence. The CH₃CHO concentration was measured using Fourier transform infrared spectroscopy, UV absorption at 184.9 nm and gas flow rates. The room temperature rate coefficient and Arrhenius expression obtained are k₁(296 K) = (1.52 ± 0.15) × 10^?11 cm³ molecule^?1 s^?1 and k₁(T) = (5.32 ± 0.55) × 10^?12 exp[(315 ± 40)/T] cm³ molecule^?1 s^?1. The rate coefficient for the reaction OH (ν = 1) + CH₃CHO, k₇(T) (where k₇ is the rate coefficient for the overall removal of OH (ν = 1)), was determined over the temperature range 204–296 K and is given by k₇(T) = (3.5 ± 1.4) × 10^?12 exp[(500 ± 90)/T], where k₇(296 K) = (1.9 ± 0.6) × 10^?11 cm³ molecule^?1 s^?1. The quoted uncertainties are 2σ (95% confidence level). The preexponential term and the room temperature rate coefficient include estimated systematic errors. k₇ is slightly larger than k₁ over the range of temperatures included in this study. The results from this study were found to be in good agreement with previously reported values of k₁(T) for temperatures <298 K. An expression for k₁(T), suitable for use in atmospheric models, in the NASA/JPL and IUPAC format, was determined by combining the present results with previously reported values and was found to be k₁(298 K) = 1.5 × 10^?11 cm³ molecule^?1 s^?1, f(298 K) = 1.1, E/R = 340 K, and Δ E/R (or g) = 20 K over the temperature range relevant to the atmosphere. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 635–646, 2008     

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 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 coefficients for the O(3P) + Cl2O gas‐phase reaction between 230 and 357 K

Rate coefficients, k, for the gas‐phase reaction of O(³P) atoms with Cl₂O (dichlorine monoxide) over a range of temperatures (230–357 K) at pressures between 12 and 32 Torr (N₂) are reported. Rate coefficients were measured under pseudo‐first‐order conditions in O(³P) using pulsed laser photolysis to produce O(³P) atoms and atomic resonance fluorescence to detect its temporal profile. The rate coefficient temperature dependence is given by the Arrhenius expression k(T) = (1.51 ± 0.20) × 10^?11 exp[?(477 ± 30)/T] cm³ molecule^?1 s^?1, and k(296 K) was measured to be (2.93 ± 0.30) × 10^?12 cm³ molecule^?1 s^?1. The quoted uncertainty limits are at the 2σ (95% confidence) level and include estimated systematic errors. The rate coefficients determined in the present study, under conditions that minimized secondary losses of O(³P), are compared with previous results from other laboratories and the discrepancies are discussed. © 2011 Wiley Peiodicals, Inc.

1 This article is a U.S. Government work and, as such, is in the public domain of the United States of America.

Int J Chem Kinet 43: 312–321, 2011     

Rate coefficients for the gas-phase OH + furan (C4H4O) reaction between 273 and 353 K

Rate coefficients, k₁, for the gas-phase OH radical reaction with the heterocyclic ether C₄H₄O (1,4-epoxybuta-1,3-diene, furan) were measured over the temperature range 273–353 K at 760 Torr (syn. air). Experiments were performed using: (i) the photochemical smog chamber THALAMOS (thermally regulated atmospheric simulation chamber, IMT NE, Douai-France) equipped with Fourier Transform Infrared (FTIR) and Selected Ion Flow Tube Mass Spectrometry (SIFT-MS) detection methods and (ii) a photochemical reactor coupled with FTIR spectroscopy (PCR, University of Crete, Greece). k₁(273–353 K) was measured using a relative rate (RR) method, in which the loss of furan was measured relative to the loss of reference compounds with well-established OH reaction rate coefficients. k₁(273–353 K) was found to be well represented by the Arrhenius expression (1.30 ± 0.12) × 10⁻¹¹ exp[(336 ± 20)/T] cm³ molecule⁻¹ s⁻¹, with k₁(296 K) measured to be (4.07 ± 0.32) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹. The k₁(296 K) and pre-exponential quoted error limits are 2σ and include estimated systematic errors in the reference rate coefficients. The observed negative temperature dependence is consistent with a reaction mechanism involving the OH radical association to a furan double bond. Quantum mechanical molecular calculations show that OH addition to the α-carbon (ΔH_r(296 K) = −121.5 kJ mol⁻¹) is thermochemically favored over the β-carbon (ΔH_r(296 K) = −52.9 kJ mol⁻¹) addition. The OH-furan adduct was found to be stable over the temperature range of the present measurements. Maleic anhydride (C₄H₂O₃) was identified as a minor reaction product, 3% lower-limit yield, demonstrating a non-ring-opening active reaction channel. The present results are critically compared with results from previous studies of the OH + furan reaction rate coefficient. The infrared spectrum of furan was measured as part of this study and its estimated climate metrics are reported.     

Temperature-dependent rate coefficients for the gas-phase OH + furan-2,5-dione (C4H2O3, maleic anhydride) reaction

Rate coefficients, k₁(T), for the gas-phase reaction of the OH radical with furan-2,5-dione (maleic anhydride (MA), C₄H₂O₃), a biomass burning related compound, were measured under pseudo–first-order conditions in OH using the pulsed laser photolysis–laser-induced fluorescence method over a range of temperature (283-374 K) and bath gas pressure (50-200 Torr; He or N₂). k₁(T) was found to be independent of pressure over this range with k₁(283-374 K) = (1.55 ± 0.20) × 10⁻¹² exp[(−410 ± 44)/T) cm³ molecule⁻¹ s⁻¹ and k₁(296 K) = (3.93 ± 0.28) × 10⁻¹³ cm³ molecule⁻¹ s⁻¹, where the uncertainties are 2σ and the preexponential term includes the estimated systematic error. The atmospheric lifetime of MA with respect to OH reactive loss is estimated to be ∼15 days. The present results are compared with a previous room temperature relative rate study of the OH + MA reaction, and the significant discrepancy between the studies is discussed; the present results are approximately a factor of 4 lower. It is also noteworthy that the experimentally measured k₁(296 K) value obtained in this work is nearly a factor of 110 less than estimated by a structure activity relationship based on trends in ionization potential. Based in part on a computational evaluation, an atmospheric degradation mechanism of MA is proposed.     

Trajectory calculations of OH radical- and Cl atom-initiated reaction of glyoxal: atmospheric chemistry of the HC(O)CO radical

On-the-fly quasi-classical trajectory calculations using the density functional method were carried out to investigate the dynamics of the HC(O)CO radical, formed by OH radical- and Cl atom-initiated reactions of glyoxal at 298 K. The energy difference between the A' HC(O)CO radical, formed immediately after H atom abstraction, and the most stable A″ HC(O)CO radical is estimated to be 6.0 kcal mol(-1). The surplus energy followed by relaxation from A' HC(O)CO to A″ HC(O)CO goes to internal energy of the nascent HC(O)CO radicals and causes prompt decomposition into HCO + CO. The average internal energy partitioned into the HC(O)CO radical is higher in the OH reaction than in the Cl reaction, in accordance with exothermicity of the reactions. A fraction of the nascent HC(O)CO radicals (91% for the OH reaction and 47% for the Cl reaction) promptly decomposes into HCO and CO within 2.5 ps. The remaining HC(O)CO radicals, which do not undergo prompt decomposition, decompose thermally or add with O(2) in the presence of O(2). I re-evaluated the previous two experiment results of the product yield ratio [CO]/[CO(2)] vs. [O(2)](-1) in the Cl atom-initiated reaction, in light of the reaction mechanism involving prompt decomposition. The two results give 9.5 × 10(6) s(-1) and 1.08 × 10(7) s(-1) for the thermal decomposition rate and 47% and 41% for the fraction of prompt decomposition in the Cl atom-initiated reaction, in good agreement with the present trajectory calculation.     

Rate constant for the reaction of OH with H2 between 200 and 480 K

The rate constant for the reaction of OH radicals with molecular hydrogen was measured using the flash photolysis resonance-fluorescence technique over the temperature range of 200-479 K. The Arrhenius plot was found to exhibit a noticeable curvature. Careful examination of all possible systematic uncertainties indicates that this curvature is not due to experimental artifacts. The rate constant can be represented by the following expressions over the indicated temperature intervals: k(H2)(250-479 K) = 4.27 x 10(-13) x (T/298)2.406 x exp[-1240/T] cm3 molecule(-1) (s-1) above T = 250 K and k(H2)(200-250 K) = 9.01 x 10(-13) x exp[-(1526 +/- 70)/T] cm3 molecule(-1) s(-1) below T = 250 K. No single Arrhenius expression can adequately represent the rate constant over the entire temperature range within the experimental uncertainties of the measurements. The overall uncertainty factor was estimated to be f(H2)(T) = 1.04 x exp[50 x /(1/T) - (1/298)/]. These measurements indicate an underestimation of the rate constant at lower atmospheric temperatures by the present recommendations. The global atmospheric lifetime of H2 due to its reaction with OH was estimated to be 10 years.     

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.     

Theoretical rate coefficients for the exchange reaction OH + D--> OD + H

In this work quasiclassical trajectory calculations were carried out to determine directly the rate coefficients for the isotopic exchange reaction, OH + D-->OD + H, using a potential-energy surface that carefully accounts for the long-range interactions. The calculated thermal rate coefficients are in good agreement with the experimental results.     

The reaction of O(1D) with H2O and the reaction of OH with C3H6

N₂O was photolyzed at 2139 Å to produce O(¹D) atoms in the presence of H₂O and CO. The O(¹D) atoms react with H₂O to produce HO radicals, as measured by CO₂ production from the reaction of OH with CO. The relative importance of the various possible O(¹D )–H₂O reactions is The relative rate constant for O(¹D) removal by H₂O compared to that by N₂O is 2.1, in good agreement with that found earlier in our laboratory. In the presence Of C₃H₆, the OH can be removed by reaction with either CO or C₃H₆: From the CO₂ yield, k₃/k₂ = 75,0 at 100°C and 55.0 at 200°C to within ± 10%. When these values are combined with the value of k₂ = 7.0 × 10^?13exp (–1100/RT) cm³/sec, k₃ = 1.36 × 10^?11 exp (–100/RT) cm³/sec. At 25°C, k₃ extrapolates to 1.1 × 10^?11 cm³/sec.     

·C2H3+O2→HC·O+H2CO 的密度泛函理论研究

应用密度泛函理论研究了@C2H3+O2→HC@O+H2CO的反应机理.在DFT(B3LYP/6-31G*)水平上对反应过程中所有反应物、中间体、过渡态和产物的几何构型进行优化,通过频率振动分析确认中间体和过渡态.计算IRC反应路径的能量,分析了中间体的异构化过程和各主要原子的自旋密度.     

Determination of the rate constant for the OH(X2Pi) + OH(X()Pi) --> O(3P) + H2O reaction over the temperature range 293-373 K

The rate constant for the reaction OH(X2Pi) + OH(X2Pi) --> O(3P) + H2O has been measured over the temperature range 293-373 K and pressure range 2.6-7.8 Torr in both Ne and Ar bath gases. The OH radical was created by 193 nm laser photolysis of N2O to produce O(1D) atoms that reacted rapidly with H2O to produce the OH radical. The OH radical was detected by quantitative time-resolved near-infrared absorption spectroscopy using Lambda-doublet resolved rotational transitions of the first overtone of OH(2,0) near 1.47 microm. The temporal concentration profiles of OH were simulated using a kinetic model, and rate constants were determined by minimizing the sum of the squares of residuals between the experimental profiles and the model calculations. At 293 K the rate constant for the title reaction was found to be (2.7 +/- 0.9) x 10(-12) cm(3) molecule(-1) s(-1), where the uncertainty includes an estimate of both random and systematic errors at the 95% confidence level. The rate constant was measured at 347 and 373 K and found to decrease with increasing temperature.     

A shock tube study of the OH + OH → H2O + O reaction

The rate coefficient for the reaction has been determined in mixtures of nitric acid (HNO₃) and argon in incident shock wave experiments. Quantitative OH time-histories were obtained by cw narrow-linewidth uv laser absorption of the R₁(5) line of the A² σ⁺ ← X² Π_i (0,0) transition at 32606.56 cm^?1 (vacuum). The experiments were conducted over the temperature range 1050–2380 K and the pressure range 0.18–0.60 atm. The second-order rate coefficient was determined to be with overall uncertainties of +11%, ?16% at high temperatures and +25%, ?22% at low temperatures. By incorporating data from previous investigations in the temperature range 298–578 K, the following expression is determined for the temperature range 298–2380 K © 1994 John Wiley & Sons, Inc.     

Energy partitioning in the reaction O(1D) + H2O → OH + OH.: The influence of O(1D) translational energy on the reaction rate constant

For the exothermic reaction O (¹D) + H₂O → OH + OH the rate constant and its energy dependence were determined by monitoring the concentration of the OH product. This was done by integrating the distribution of product molecules over all accessible states. The rate constant, determined at different velocity distributions of the reacting metastable over a wide range, is energy independent.     

Experimental and theoretical studies of rate coefficients for the reaction O(3P)+C2H5OH at high temperatures

Rate coefficients of the reaction O(3P)+C2H5OH in the temperature range 782-1410 K were determined using a diaphragmless shock tube. O atoms were generated by photolysis of SO2 at 193 nm with an ArF excimer laser; their concentrations were monitored via atomic resonance absorption. Our data in the range 886-1410 K are new. Combined with previous measurements at low temperature, rate coefficients determined for the temperature range 297-1410 K are represented by the following equation: k(T)=(2.89+/-0.09)x10(-16)T1.62 exp[-(1210+/-90)/T] cm3 molecule(-1) s(-1); listed errors represent one standard deviation in fitting. Theoretical calculations at the CCSD(T)/6-311+G(3df, 2p)//B3LYP/6-311+G(3df) level predict potential energies of various reaction paths. Rate coefficients are predicted with the canonical variational transition state (CVT) theory with the small curvature tunneling correction (SCT) method. Reaction paths associated with trans and gauche conformations are both identified. Predicted total rate coefficients, 1.60 x 10(-22)T3.50 exp(16/T) cm3 molecule(-1) s(-1) for the range 300-3000 K, agree satisfactorily with experimental observations. The branching ratios of three accessible reaction channels forming CH3CHOH+OH (1a), CH2CH2OH+OH (1b), and CH3CH2O+OH (1c) are predicted to vary distinctively with temperature. Below 500 K, reaction 1a is the predominant path; the branching ratios of reactions 1b,c become approximately 40% and approximately 11%, respectively, at 2000 K.     

Differential and integral cross sections for the H + O2 --> OH + O combustion reaction

We present accurate differential and integral cross sections for the H + O2 --> OH + O reaction obtained on a newly developed ab initio potential energy surface using time-independent and time-dependent quantum mechanical methods. The product angular distributions near the reaction threshold show pronounced forward and backward peaks, reflecting the complex-forming mechanism. However, the asymmetry of these peaks suggests certain nonstatistical behaviors, presumably due to some relatively short-lived resonances. The integral cross section increases monotonically with the collision energy above a reaction threshold.     

State-to-state reaction probabilities for the H+O2(v,j)-->O+OH(v',j') reaction on three potential energy surfaces

We report state-to-state and total reaction probabilities for J=0 and total reaction probabilities for J=2 and 4 for the title reaction, both for ground-state and initially rovibrationally excited reactants. The results for three different potential energy surfaces are compared and contrasted. The potential energy surfaces employed are the DMBE IV surface by Pastrana et al. [J. Phys. Chem. 94, 8073 (1990)], the surface by Troe and Ushakov (TU) [J. Chem. Phys. 115, 3621 (2001)], and the new XXZLG ab initio surface by Xu et al. [J. Chem. Phys. 122, 244305 (2005)]. Our results show that the total reaction probabilities from both the TU and XXZLG surfaces are much smaller in magnitude for collision energies above 1.2 eV compared to the DMBE IV surface. The three surfaces also show different behavior with regards to the effect of initial state excitation. The reactivity is increased on the XXZLG and the TU surfaces and decreased on the DMBE IV surface. Vibrational and rotational product state distributions for the XXZLG and the DMBE IV surface show different behaviors for both types of distributions. Our results show that for energies above 1.25 eV the dynamics on the DMBE IV surface are not statistical. However, there is also evidence that the dynamics on the XXZLG surface are not purely statistical for energies above the onset of the first excited product vibrational state v'=1. The magnitude of the total reaction probability is decreased for J>0 for the DMBE IV and the XXZLG surfaces for ground-state reactants. However, for initially rovibrationally excited reactants, the total reaction probability does not decrease as expected for both surfaces. As a result the total cross section averaged over all Boltzmann accessible rotational states may well be larger than the cross section reported in the literature for j=1.