A computational study of the kinetics and mechanism for the reaction of HCO with HNO

The mechanism for the reaction of HCO with HNO has been studied at the G2M level of theory, based on the geometric parameters optimized by the BH&HLYP/6‐311G(d, p) method. There are three direct hydrogen abstraction channels producing (1) H₂CO + NO, (2) H₂NO + CO, and (3) HNOH + CO with barriers of 3.7, 3.9, and 10.4 kcal/mol, respectively. Another important reaction channel, (4), involves an association process forming HN(O)CHO (LM1) with a very small barrier and the subsequent isomerization and decomposition of LM1 producing HNOH + CO as major products. The rate constants of the dominant reaction channels (1), (2), and (4) in the temperature range 200–3000 K have been predicted by the microcanonical RRKM and transition state theory calculations with Eckart tunneling corrections. The theoretical result shows that in the high temperature range ( T > 1500 K), k₁ (H₂CO + NO) and k₂(H₂NO + CO) are preponderant, while in the low temperature range, both k₄(LM1) and k₄(HNOH + CO) appear to be dominant at high and low pressures, respectively. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 205–215, 2004     

Probing the pyrolysis of ethyl formate in the dilute gas phase by synchrotron radiation and theory

The thermal decomposition of the atmospheric constituent ethyl formate was studied by coupling flash pyrolysis with imaging photoelectron photoion coincidence (iPEPICO) spectroscopy using synchrotron vacuum ultraviolet (VUV) radiation at the Swiss Light Source (SLS). iPEPICO allows photoion mass-selected threshold photoelectron spectra (ms-TPES) to be obtained for pyrolysis products. By threshold photoionization and ion imaging, parent ions of neutral pyrolysis products and dissociative photoionization products could be distinguished, and multiple spectral carriers could be identified in several ms-TPES. The TPES and mass-selected TPES for ethyl formate are reported for the first time and appear to correspond to ionization of the lowest energy conformer having a cis (eclipsed) configuration of the O = C (H)– O – C (H₂)–CH₃ and trans (staggered) configuration of the O= C (H)– O – C (H₂)– C H₃ dihedral angles. We observed the following ethyl formate pyrolysis products: CH₃CH₂OH, CH₃CHO, C₂H₆, C₂H₄, HC(O)OH, CH₂O, CO₂, and CO, with HC(O)OH and C₂H₄ pyrolyzing further, forming CO + H₂O and C₂H₂ + H₂. The reaction paths and energetics leading to these products, together with the products of two homolytic bond cleavage reactions, CH₃CH₂O + CHO and CH₃CH₂ + HC(O)O, were studied computationally at the M06-2X-GD3/aug-cc-pVTZ and SVECV-f12 levels of theory, complemented by further theoretical methods for comparison. The calculated reaction pathways were used to derive Arrhenius parameters for each reaction. The reaction rate constants and branching ratios are discussed in terms of the residence time and newly suggest carbon monoxide as a competitive primary fragmentation product at high temperatures.     

Mechanistic Study of Ozone-Water Reaction and Their Reaction Products with Gas Phase Elemental Mercury:A Computational Study

The interaction of oxygen of water and central oxygen of ozone produces stable H₂O‐O₃ complex with no barrier. With decomposition of this complex through H‐abstraction by O₃ and O‐abstraction by H₂O, four possible product channels have been found. The reaction of mercury and the products of water‐ozone reaction have been studied. All geometrical and AIM parameters of intermediate, transition states, and the products of reactions are calculated and thermodynamic parameters are obtained. The negative value of free energy show that channels Hg+H₂OO, Hg+H₂O₂ and Hg+H₂O₄ in hydrogen tetroxide form (HTO) may be the main reaction channels.     

The atmospheric chemistry of the HC(O)CO radical

The chemistry of the HC(O)CO radical, produced in the oxidation of glyoxal, has been studied under conditions relevant to the lower atmosphere using an environmental chamber/Fourier Transform infrared spectrometric system. The chemistry of HC(O)CO was studied over the range 224–317 K at 700 Torr total pressure and was found to be governed by competition between unimolecular decomposition [to HCO and CO, reaction (5)] and reaction with O₂ [to form HO₂ and 2CO, reaction (6a), or HC(O)C(O)O₂, reaction (6b)]. The rate coefficient for decomposition relative to that of reaction with O₂ increases with increasing temperature. Assuming a value for k₆ of 10⁻¹¹ cm³ molecule⁻¹ s⁻¹, the following expression for the unimolecular decomposition is obtained at 700 Torr, k₅ = 1.4⁺⁹/_−1.1 × 10¹² exp(−3160 ± 500/T). The rate coefficients for reactions (6a) and (6b) are about equal, with no strong dependence on temperature. The reaction of HC(O)C(O)O₂ with NO₂ was also studied. Final product analysis was consistent with the formation of HCO, CO₂, and NO₃ as the major products in this reaction; no evidence for the PAN‐type species, HC(O)C(O)O₂NO₂, was found even at the lowest temperature studied (224 K). The UV‐visible absorption spectrum of glyoxal is also reported; results are in substantive agreement with previous studies. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 149–156, 2001     

Theoretical Study of the Rate Coefficients for CH3NHNH2 + NO2 and Related Reactions

The kinetics and mechanisms of H atom abstraction reactions from CH₃NHNH₂ by NO₂ (R1) and related reactions have been investigated theoretically by using ωB97X‐D and CCSD(T)‐F12 quantum chemical calculations and the steady‐state unimolecular master equation analysis based on Rice–Ramsperger–Kassel–Marcus (RRKM) theory. For reaction (R1), both dissociation and isomerization steps between intermediate complexes were found to be important for the distribution of the dissociated bimolecular products. The dominant products of (R1) were found to be cis‐CH₃NHNH and HONO at lower temperature. The branching ratios for CH₃NNH₂ formation paths increased with increasing temperature. On the same reaction potential energy surface, six reactions including isomerization reactions between CH₃NNH₂ and cis‐/trans‐CH₃NHNH catalyzed by HONO were suggested to compete with the reverse reaction of (R1). The temperature‐ and pressure‐dependent rate expressions are proposed for kinetic modeling.     

Validation of a thermal decomposition mechanism of formaldehyde by detection of CH2O and HCO behind shock waves

The thermal decomposition of formaldehyde was investigated behind shock waves at temperatures between 1675 and 2080 K. Quantitative concentration time profiles of formaldehyde and formyl radicals were measured by means of sensitive 174 nm VUV absorption (CH₂O) and 614 nm FM spectroscopy (HCO), respectively. The rate constant of the radical forming channel (1a), CH₂O + M → HCO + H + M, of the unimolecular decomposition of formaldehyde in argon was measured at temperatures from 1675 to 2080 K at an average total pressure of 1.2 bar, k_1a = 5.0 × 10¹⁵ exp(‐308 kJ mol^?1/RT) cm³ mol^?1 s^?1. The pressure dependence, the rate of the competing molecular channel (1b), CH₂O + M → H₂ + CO + M, and the branching fraction β = k_1a/(kA_1a + k_1b) was characterized by a two‐channel RRKM/master equation analysis. With channel (1b) being the main channel at low pressures, the branching fraction was found to switch from channel (1b) to channel (1a) at moderate pressures of 1–50 bar. Taking advantage of the results of two preceding publications, a decomposition mechanism with six reactions is recommended, which was validated by measured formyl radical profiles and numerous literature experimental observations. The mechanism is capable of a reliable prediction of almost all formaldehyde pyrolysis literature data, including CH₂O, CO, and H atom measurements at temperatures of 1200–3200 K, with mixtures of 7 ppm to 5% formaldehyde, and pressures up to 15 bar. Some evidence was found for a self‐reaction of two CH₂O molecules. At high initial CH₂O mole fractions the reverse of reaction (6), CH₂OH + HCO ? CH₂O + CH₂O becomes noticeable. The rate of the forward reaction was roughly measured to be k₆ = 1.5 × 10¹³ cm³ mol^?1 s^?1. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 157–169 2004     

Experimental measurements and kinetic modeling of CO/H2/O2/NOx conversion at high pressure

This paper presents results from lean CO/H₂/O₂/NO_x oxidation experiments conducted at 20–100 bar and 600–900 K. The experiments were carried out in a new high‐pressure laminar flow reactor designed to conduct well‐defined experimental investigations of homogeneous gas phase chemistry at pressures and temperatures up to 100 bar and 925 K. The results have been interpreted in terms of an updated detailed chemical kinetic model, designed to operate also at high pressures. The model, describing H₂/O₂, CO/CO₂, and NO_x chemistry, is developed from a critical review of data for individual elementary reactions, with supplementary rate constants determined from ab initio CBS‐QB3 calculations. New or updated rate constants are proposed for important reactions, including OH + HO₂ ? H₂O + O₂, CO + OH ? [HOCO] ? CO₂ + H, HOCO + OH ? CO + H₂O₂, NO₂ + H₂ ? HNO₂ + H, NO₂ + HO₂ ? HONO/HNO₂ + O₂, and HNO₂(+M) ? HONO(+M). Further validation of the model performance is obtained through comparisons with flow reactor experiments from the literature on the chemical systems H₂/O₂, H₂/O₂/NO₂, and CO/H₂O/O₂ at 780–1100 K and 1–10 bar. Moreover, introduction of the reaction CO + H₂O₂ → HOCO + OH into the model yields an improved prediction, but no final resolution, to the recently debated syngas ignition delay problem compared to previous kinetic models. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 454–480, 2008     

Kinetics for the hydrogen‐abstraction of CH4 with NO2

The detailed mechanism of the NO₂+CH₄ reaction has been computationally investigated at the M06‐2X/MG3S, B3LYP/6‐311G(2d,d,p), and MP2/6‐311+G(2df,p) levels. The direct dynamics calculations were preformed using canonical transition state theory with tunneling correction and scaled generalized normal‐mode frequencies including anharmonic torsion. The calculated results indicate that the NO₂+CH₄ reaction proceeds by three distinct channels simultaneously, leading to the formation of trans‐HONO (1a), cis‐HONO (1b), and HNO₂ (1c), and each channel involves the formation of intermediate having lower energy than the final product. The anti‐Hammond behavior observed in channel 1a is well analyzed. Proper treatment of anharmonic torsions about the C···H···O (or N) axis in the transition structures greatly improves the accuracy of kinetics predictions. The activation energy for each channel increases substantially with temperature, but is not strictly a linear function of temperature. Therefore, the thermal rate constants are fitted to the four‐parameter expression recommended for this case over the wide temperature range 400–4000 K. © 2012 Wiley Periodicals, Inc.     

Theoretical investigation on the reaction of N2O and CO catalyzed by Fe(C6H6)

The reaction of N₂O with CO, catalyzed by Fe⁺(C₆H₆) and producing N₂ and CO₂, has been investigated at the UB3LYP/6-311+G(d) level. The computation results revealed that the reaction of Fe⁺(C₆H₆), N₂O and CO, is an O-atom abstraction mechanism. For the reaction channels, the geometries and the vibrational frequencies of all species have been calculated and the frequency modes analysis also have been given to elucidate the reaction mechanism. On the basis for geometry optimizations, the thermodynamic data of these reactions channels have been calculated using the statistical theory at 295.15 K and pressure of 0.35 Torr. Using Eyring transition state theory with Wigner correction, the activation thermodynamic data, rate constant and frequency factors for the these reaction channels also have been given. The results showed that CO and N₂O do not react without catalyst and Fe⁺(C₆H₆) can excellently mediate the reaction of N₂O and CO.     

HCO+NO2反应势能面的理论研究

在B3LYP/6-311G(d,p)和CCSD(T)/6-311G(d,p)水平上给出了HCO+NO₂反应详细的势能面信息.计算结果表明,该反应采用两种无垒进攻方式,分别得到两种加合物H(O)CNO₂和H(O)CONO.找到7种能量低于反应物且合理的产物及相应的反应路径.通过对热力学和动力学的分析,产物HONO+CO(P2,P3),HNO+CO₂(P1)和H+CO₂+NO(P6)的形成更为有利.计算结果同实验相符,且有助于深入了解HCO自由基的化学行为.     

An FTIR product study of the reaction between HCO and NO2

The product distribution of the reaction (1a) $$\rm\longrightarrow OH+NO+CO$$ (1b) $$\rm\longrightarrow HNO+CO_{2}$$ (1c) $$\rm\longrightarrow H+NO+CO_{2}$$ (1d) $$\rm\longrightarrow HCO_{2}+NO$$ (1e) (1f) (1g) was investigated at room temperature in the gas phase in Ar buffer gas at 570 mbar pressure by Fourier transform infrared (FTIR) spectroscopy. Mixtures of NO₂/H₂CO/Ar were photolyzed under stationary conditions using a high‐pressure Hg lamp at λ = 300–340 nm. NO, CO, CO₂, HONO, and H₂O were found as major reaction products. A small amount of N₂O was detected at long reaction times. From the yields of CO and CO₂, branching ratios were found to be (k_1a + k_1b)/k₁ = (0.66 ± 0.10) and (k_1c + k_1d + k_1e)/k₁ = (0.34 ± 0.10). The formation of HONO was attributed to reaction ( 1a ) and/or reaction ( 1c ) followed by the reaction HNO + NO₂ → NO + HONO with a combined branching ratio of (k_1a + k_1c)/k₁ = (0.28 ± 0.10). © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 136–145, 2000     

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     

Kinetics and mechanism for the CH2O + NO2 reaction: A computational study

The reactants, products, and transition states of the CH₂O + NO₂ reaction on the ground electronic potential energy surface have been searched at both B3LYP/6?311+G(d,p) and MPW1PW91/6?311+G(3df,2p) levels of theory. The forward and reverse barriers are further improved by a modified Gaussian‐2 method. The theoretical rate constants for the two most favorable reaction channels 1 and 2 producing CHO + cis‐HONO and CHO + HNO₂, respectively, have been calculated over the temperature range from 200 to 3000 K using the conventional and variational transition‐state theory with quantum‐mechanical tunneling corrections. The former product channel was found to be dominant below 1500 K, above which the latter becomes competitive. The predicted total rate constants for these two product channels can be presented by k_t (T) = 8.35 × 10^?11 T^6.68 exp(?4182/T) cm³/(mol s). The predicted values, which include the significant effect of small curvature tunneling corrections, are in quantitative agreement with the available experimental data throughout the temperature range studied (390–1650 K). © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 184–190, 2003     

Mechanism and Rate Constants of the CH3+ CH2CO Reaction: A Theoretical Study

The mechanism of the reaction of ketene with methyl radical has been studied by ab initio CCSD(T)‐F12/cc‐pVQZ‐f12//B2PLYPD3/6‐311G** calculations of the potential energy surface. Temperature‐ and pressure‐dependent reaction rate constants have been computed using the Rice–Ramsperger–Kassel–Marcus (RRKM)–Master Equation and transition state theory methods. Three main channels have been shown to dominate the reaction; the formation of the collisionally stabilized CH₃COCH₂ radical and the production of the C₂H₅ + CO and HCCO + CH₄ bimolecular products. Relative contributions of the CH₃COCH₂, C₂H₅ + CO, and HCCO + CH₄ channels strongly depend on the reaction conditions; the formation of thermalized CH₃COCH₂ is favored at low temperatures and high pressures, HCCO + CH₄ is dominant at high temperatures, whereas the yield of C₂H₅ + CO peaks at intermediate temperatures around 1000 K. The C₂H₅ + CO channel is favored by a decrease in pressure but remains the second most important reaction pathway after HCCO + CH₄ under typical flame conditions. The calculated rate constants at different pressures are proposed for kinetic modeling of ketene reactions in combustion in the form of modified Arrhenius expressions. Only rate constant to form CH₃COCH₂ depends on pressure, whereas those to produce C₂H₅ + CO and HCCO + CH₄ appeared to be pressure independent.     

Ab initio Mechanism Study on the Reaction of Chlorine Atom with Formic Acid

The potential energy surface(PES) for the reaction of Cl atom with HCOOH is predicted using ab initio molecular orbital calculation methods at UQCIDS(T,full)6-311 G(3df,2p)//UMP2(full)/6-311 G(d,P) level of theory with zero-point vibrational energy (ZPVE) correction.The calculated results show that the reaction mechanism of Cl atom with formic acid is a C-site hydrogen abstraction reaction from cis-HOC(H)O molecule by Cl atom with a 3.73kJ/mol reaction barrier height,leading to the formation of cis-HOCO radical which will reacts with Cl atom or other molecules in such a reaction system.Because the reaction barrier height of O-site hydrogen abstraction reaction from cis-HOC(H)O molecule by Cl atom which leads to the formation of HCO2 radical is 67.95kJ/mol,it is a secondary reaction channel in experiment,This is in good agreement with the prediction based on the previous experiments.     

Ab initio MO and TST calculations for the rate constant of the HNO+NO2→HONO+NO reaction

Potential-energy surfaces for various channels of the HNO+NO₂ reaction have been studied at the G2M(RCC,MP2) level. The calculations show that direct hydrogen abstraction leading to the NO+cis-HONO products should be the most significant reaction mechanism. Based on TST calculations of the rate constant, this channel is predicted to have an activation energy of 6–7 kcal/mol and an A factor of ca. 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ at ambient temperature. Direct H-abstraction giving NO+trans-HONO has a high barrier on PES and the formation of trans-HONO would rather occur by the addition/1,3-H shift mechanism via the HN(O)NO₂ intermediate or by the secondary isomerization of cis-HONO. The formation of NO+HNO₂ can take place by direct hydrogen transfer with the barrier of ca. 3 kcal/mol higher than that for the NO+cis-HONO channel. The formation of HNO₂ by oxygen abstraction is predicted to be the least significant reaction channel. The rate constant calculated in the temperature range 300–5000 K for the lowest energy path producing NO+cis-HONO gave rise to © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 729–736, 1998     

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.     

Photodissociation Dynamics of Benzaldehyde (C6H5CHO) at 266, 248, and 193 nm

The photodissociation of gaseous benzaldehyde (C₆H₅CHO) at 193, 248, and 266 nm using multimass ion imaging and step‐scan time‐resolved Fourier‐transform infrared emission techniques is investigated. We also characterize the potential energies with the CCSD(T)/6‐311+G(3df,2p) method and predict the branching ratios for various channels of dissociation. Upon photolysis at 248 and 266 nm, two major channels for formation of HCO and CO, with relative branching of 0.37:0.63 and 0.20:0.80, respectively, are observed. The C₆H₅+HCO channel has two components with large and small recoil velocities; the rapid component with average translational energy of approximately 25 kJ mol^?1 dominates. The C₆H₆+CO channel has a similar distribution of translational energy for these two components. IR emission from internally excited C₆H₅CHO, ν₃ (v=1) of HCO, and levels v≤2, J≤43 of CO are observed; the latter has an average rotational energy of approximately 13 kJ mol^?1 and vibrational energy of approximately 6 kJ mol^?1. Upon photolysis at 193 nm, similar distributions of energy are observed, except that the C₆H₅+HCO channel becomes the only major channel with a branching ratio of 0.82±0.10 and an increased proportion of the slow component; IR emission from levels ν₁ (v=1) and ν₃ (v=1 and 2) of HCO and v≤2, J≤43 of CO are observed; the latter has an average energy similar to that observed in photolysis at 248 nm. The observed product yields at different dissociation energies are compared to statistical‐theory predicted results based on the computed singlet and triplet potential‐energy surfaces.     

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.     

FTIR研究HCO自由基与NO2反应的动力学

为了减少和控制油品在燃烧时 NOx的排放 ,对 NOx再燃烧进程的动力学研究一直受到人们的关注 [1,2].迄今为止 ,对于该进程中的一些可能参与的基元化学反应知道甚少 .从实验测得的总速率常数看 ,在室温下 ,主反应 HCO自由基与 NO2的反应是一个相当快速的反应 [3],其总速率常数约为 3.3× 1013 cm3· mol－ 1· s－ 1.但是 ,有关该反应体系的产物分布情况及其反应机理目前还未见报导 .该反应体系在热力学上存在着下列 放热反应 [4]:　　反应 [1a－ 1e]可在低压条件下发生 ,而反应 [1f－ 1g]只能在高压范围内产生 [5,6].本文是以高纯度的甲…