A shock tube study of the reactions of CH with CO2 and O2

The formation and consumption of CH radicals during shock-induced pyrolysis of a few ppm ethane diluted in argon was measured by a ring-dye laser spectrometer. Absorption-over-time profiles, measured at a resonance line in the Q-branch of the A²Δ − X²Π band of CH at λ = 431.1311 nm, were recorded and transformed into CH concentrations by known absorption coefficients. By adding some hundred ppm of CO₂ or O₂ to the initial mixtures, the CH concentration profiles were significantly perturbed. Both the perturbed and unperturbed CH concentration profiles have been compared with calculations based on a reaction kinetic model. A sensitivity analysis revealed that the perturbation process was dominated by direct reactions of CH with the added molecules. By fitting calculated to observed CH profiles the following rate coefficients were obtained The experiments were performed in the temperature range between 2500 K and 3500 K. © 1996 John Wiley & Sons, Inc.     

A shock tube study of the pyrolysis of NO2

NO₂ concentration profiles in shock-heated NO₂/Ar mixtures were measured in the temperature range of 1350–2100 K and pressures up to 380 atm using Ar⁺ laser absorption at 472.7 nm, IR emission at 6.25±0.25 μm, and visible emission at 300–600 nm. In the course of this study, the absorption coefficient of NO₂ at 472.7 nm was measured at temperatures from 300 K to 2100 K and pressures up to 75 atm. Rate coefficients for the reactions NO₂+M→NO+O+M (1), NO₂+NO₂→2NO+O₂ (2a), and NO₂+NO₂→NO₃+NO (2b) were derived by comparing the measured and calculated NO₂ profiles. For reaction (1), the following low- and high-pressure limiting rate coefficients were inferred which describe the measured fall-off curves in Lindemann form within 15% [FORMULA] The inferred rate coefficient at the low- pressure limit, k_1o, is in good agreement with previous work at higher temperatures, but the energy of activation is lower by 20 kJ/mol than reported previously. The pressure dependence of k₁ observed in the earlier work of Troe [1] was confirmed. The rate coefficient inferred for the high pressure limit, k_1∞, is higher by a factor of two than Troe's value, but in agreement with data obtained by measuring specific energy-dependent rate coefficients. For the reactions (2a) and (2b), least-squares fits of the present data lead to the following Arrhenius expressions: [FORMULA] For reaction (2), the new data agree with previously recommended values of k_2a and k_2b, although the present study suggests a slightly higher preexponential factor for k_2a. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 483–493, 1997.     

A shock tube study of the CH2O + NO2 reaction at high temperatures

The reaction of CH₂O with NO₂ has been studied with a shock tube equipped with two stabilized ew CO lasers. The production of CO, NO, and H₂O has been monitored with the CO lasers in the temperature range of 1140–1650 K using three different Ar-diluted CH₂O-NO₂ mixtures. Kinetic modeling and sensitivity analysis of the observed CO, NO, and H₂O production profiles over the entire range of reaction conditions employed indicate that the bimolecular metathetical reaction, NO₂ + CH₂O → HONO + CHO (1) affects most strongly the yields of these products. Combination of the kinetically modeled values of ??₁ with those obtained recently from a low temperature pyrolytic study, ref. [8], leads to for the broad temperature range of 300–2000 K.     

Interaction between NH2NO and H2O2: A quantum chemistry study

The H‐bonded complexes formed from interaction between NH₂NO (NA) and H₂O₂ (HP) have been investigated by using B3LYP and MP2 methods with a wide range of basis sets. We found six H‐bonded complexes in which three of them have cyclic structure. Calculations carried out at various levels show that the seven‐membered cyclic structure with O···HO and O···HN hydrogen bonding interactions is the most stable complex. The large binding energy obtained for A1 complex probably results from a more linear arrangement of the O···H N and O H···OH‐bonds in the seven‐membered structure A1. The natural bond orbital (NBO) analysis and the Bader's quantum theory of atoms in molecules have been used to elucidate the interaction characteristics of the NA‐HP complexes. The NBO results reveal that the charge transfer energy corresponds to the H‐bond interactions for A1 complex is grater than other complexes. The electrostatic nature of H‐bond interactions is predicted from QTAIM analysis. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

An investigation of the reactions of H3O+ and O2+ with NO, NO2, N2O and HNO2 in support of selected ion flow tube mass spectrometry

A selected ion flow tube (SIFT) experimental investigation has been carried out of the reactions of H3O+, NO+ and O2+ with NO, NO2, N2O and HNO2, in order to obtain the essential kinetic data for the analyses of these compounds in air using selected ion flow tube mass spectrometry (SIFT-MS). These investigations show that NO+ ions do not react at a significant rate with any of these NOx compounds and that H3O+ ions react only with HNO2 (product ions H2NO2+ (75%) and NO+ (25%)). O2+ ions react with NO (product ion NO+), NO2 (product ion NO2+) and HNO2 (product ions NO+ (75%), NO2+ (25%)), but not with N2O. We conclude that both NO and NO2 can be accurately quantified in air using only O2+ precursor ions and SIFT-MS when HNO2 is not present. However, when HNO2 is present it invariably co-exists with both NO and NO2 and then both H3O+ and O2+ precursor ions are needed to determine the partial pressures of NO, NO2 and HNO2 in the air mixture. We also conclude that currently N2O cannot be analysed in air using SIFT-MS.     

The reactions of isotopically labeled N15NO+ with CO,NO, O2, N2, NO2, and N2O

The reactions of labeled N¹⁵NO⁺ with CO, NO, O₂, ¹⁸O₂, N₂, NO₂, and N₂O have been investigated using a tandem ICR instrument. In each case the total rate coefficient, product distribution, and kinetic energy dependence were measured. The results indicate that very specific reaction mechanisms govern these reactions. This conclusion is suggested by the lack of isotopic scrambling in many cases and by the complete absence of energetically allowed products in almost all of the systems. The kinetic energy studies indicate that most of the reaction channels proceed through an intermediate complex at low energies and via a direct mechanism at higher kinetic energies. Such direct mechanisms include long range charge transfer and atom or ion transfer.     

Theoretical study of reactions of N2O with NO and OH radicals

The reactions of N₂O with NO and OH radicals have been studied using ab initio molecular orbital theory. The energetics and molecular parameters, calculated by the modified Gaussian-2 method (G2M), have been used to compute the reaction rate constants on the basis of the TST and RRKM theories. The reaction N₂O + NO → N₂ + NO₂ (1) was found to proceed by direct oxygen abstraction and to have a barrier of 47 kcal/mol. The theoretical rate constant, k₁ = 8.74 × 10⁻¹⁹ × T^2.23 exp (−23,292/T) cm³ molecule⁻¹ s⁻¹, is in close agreement with earlier estimates. The reaction of N₂O with OH at low temperatures and atmospheric pressure is slow and dominated by association, resulting in the HONNO intermediate. The calculated rate constant for 300 K ≤ T ≤ 500 K is lower by a few orders than the upper limits previously reported in the literature. At temperatures higher than 1000 K, the N₂O + OH reaction is dominated by the N₂ + O₂H channel, while the HNO + NO channel is slower by 2–3 orders of magnitude. The calculated rate constants at the temperature range of 1000–5000 K for N₂O + OH → N₂ + O₂H (2A) and N₂O + OH → HNO + NO (2B) are fitted by the following expressions: in units of cm³ molecule ⁻¹s⁻¹. Both N₂O + NO and N₂O + OH reactions are confirmed to enhance, albeit inefficiently, the N₂O decomposition by reducing its activation energy. © 1996 John Wiley & Sons, Inc.     

A shock tube study of reactions of atomic oxygen with isocyanic acid

Reactions of atomic oxygen with isocyanic acid (HNCO) have been studied in incident and reflected shock wave experiments using HNCO/N₂O/Ar mixtures. Quantitative time-histories of the NH(X³Σ^?) and OH(X²Π_i) radicals were measured behind the shock waves using cw, narrow-linewidth laser absorption at 336 nm and 307 nm, respectively. The second-order rate coefficients of the reactions: and were determined from early-time NH and OH formation rates, with least-squares two-parameter fits of the results given by: and cm³ mol^?1 s^?1. The minimum and maximum rate constant factors (?,F) define the lower and upper uncertainty limits, respectively. An upper limit on the rate coefficient of was determined to be: .     

A shock tube study of H + HNCO → NH2 + CO

The reaction of atomic hydrogen with isocyanic acid (HNCO) to produce the amidogen radical (NH₂) and carbon monoxide, has been studied in shock-heated mixtures of HNCO dilute in argon. Time-histories of the ground-state NH₂ radical were measured behind reflected shock waves using cw, narrowlinewidth laser absorption at 597 nm, and HNCO time-histories were measured using infrared emission from the fundamental v₂-band of HNCO near 5 μm. The second-order rate coefficient of reaction (2(a)) was determined to be: cm³ mol^?1 s^?1, where f and F define the lower and upper uncertainty limits, respectively. An upper limit on the rate coefficient of was determined to be:      

A kinetic study of the gas‐phase reactions of OIO with NO,NO2, and Cl2

The kinetics of iodine dioxide (OIO) reactions with nitric oxide (NO), nitrogen dioxide (NO₂), and molecular chlorine (Cl₂) are studied in the gas‐phase by cavity ring‐down spectroscopy. The absorption spectrum of OIO is monitored after the laser photodissociation, 266 or 355 nm, of the gaseous mixture, CH₂I₂/O₂/N₂, which generates OIO through a series of reactions. The second‐order rate constant of the reaction OIO + NO is determined to be (4.8 ± 0.9) × 10^?12 cm³ molecule^?1 s^?1 under 30 Torr of N₂ diluent at 298 K. We have also measured upper limits for the second‐order rate constants of OIO with NO₂ and Cl₂ to be k < 6 × 10^?14 cm³ molecule^?1 s^?1 and k < 8 × 10^?13 cm³ molecule^?1 s^?1, respectively. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 688–693, 2007     

Shock tube measurements of the reactions of CN with O and O2

The rate coefficients of the reactions and were determined in a series of shock tube experiments from CN time histories recorded using a narrow-linewidth cw laser absorption technique. The ring dye laser source generated 388.44 nm radiation corresponding to the CN B²Σ⁺(v = 0) ← X²Σ⁺(v = 0) P-branch bandhead, enabling 0.1 ppm detection sensitivity. Reaction (1) was measured in shock-heated gas mixtures of typically 200 ppm N₂O and 10 ppm C₂N₂ in argon in the temperature range 3000 to 4500 K and at pressures between 0.45 and 0.90 atm. k₁ was determined using pseudo-first order kinetics and was found to be 7.7 × 10¹³ (±20%) [cm³ mol^?1 s^?1]. This value is significantly higher than reported by earlier workers. Reaction (2) was measured in two regimes. In the first, nominal gas mixtures of 500 ppm O₂ and 10 ppm C₂N₂ in argon were shock heated in the temperature range 2700 K to 3800 K and at pressures between 0.62 and 1.05 atm. k₂ was determined by fitting the measured CN profiles with a detailed mechanism. In the second regime, gas mixtures of 500 ppm O₂ and 1000 ppm C₂N₂ in argon were shock heated in the temperature range 1550 to 1950 K and at pressures between 1.19 and 1.57 atm. Using pulsed radiation from an ArF excimer laser at 193 nm, a fraction of the C₂N₂ was photolyzed to produce CN. Pseudo-first order kinetics were used to determine k₂. Combining the results from both regimes, k₂ was found to be 1.0 × 10¹³ (±20%) [cm³ mol^?1 s^?1].     

Gas-phase reactions and rearrangements of alkyl esters with H3O+, NO+, and O2*+: a selected ion flow tube study

Selected ion flow tube mass spectrometry (SIFT-MS) has been employed to study the ion-molecule reactions of 17 alkyl esters reacting with the common SIFT-MS reagent ions, H3O+, H3O+.nH2O (n = 1, 2, 3), NO+, and O2+. The majority of reactions were observed to proceed at or near collision rate, with the exception of H3O+.3H2O, which was found to be slow for 8 of 17 alkyl esters. Unexpected product ions in the form of the parent carboxylic acid cation were observed to arise from the H3O+ and NO+ reactions of some alkyl esters. The observed reactions have been probed by the ab initio CBS-4M and G2(MP2,SVP) methods. The postulated reaction pathway involves a 1,5 H atom migration from a beta-carbon onto the carbonyl oxygen.     

A shock tube study of the reactions of the hydroxyl radical with several combustion species

Reactions of the hydroxyl radical, OH, with several organic species of interest in combustion chemistry have been studied near 1200 K and 1 atm in shock tube experiments in which UV absorption was used to monitor the OH concentration. Rate coefficients were measured for the reactions of OH with 2,3-dimethylbutane, isooctane, neooctane, ethylene, propylene, acetylene, formaldehyde, methanol, and ethanol. The values were found to be (in units of 10¹² cm³/mol-s): 21, 22, 18, 2.6, 9.6, 0.28, 12, 5.2, and 5.3. These measured values are compared with previous experimental results and, where appropriate, transition-state theory calculations.     

NO 和 NO2 在 V2O5/AC 催化剂表面的反应行为

 采用程序升温脱附、在线质谱和原位漫反射红外光谱等手段, 比较了 NO 和 NO2 在 V2O5 及 V2O5/AC 催化剂表面的选择催化还原 (SCR) 反应行为. 结果表明, 氨以质子态 NH4+和共价态 NH3 分子两种形态吸附于纯 V2O5 表面, V=O 为氨的主要吸附活性位. 无氧状态下, NO 和 NO2 皆可与吸附于 V2O5 表面的 NH3 反应, 并且 NO2 与吸附态 NH3 的反应活性高于 NO. 但在 V2O5/AC 催化剂表面, 同样在无氧条件下, NO 几乎不与吸附态 NH3 反应, 而 NO2 却可以反应并生成 N2. 在 V2O5/AC 表面, NO 很容易被气相 O2 氧化为 NO2, 然后参与 SCR 反应. 可见, NO2 是 NO 在 V2O5/AC 表面发生 SCR 反应的中间体.     

Kinetics of the reactions of the CHBr2 and CHBr2O2 radicals with O2 and NO

When bromoform (CHBr3) is photolyzed at 266 or 303 nm in the presence of O2 and NO, the formation of secondary Br atoms is observed. By following the rate of growth of this secondary Br atom signal as a function of conditions, rate constants have been determined for the reactions CHBr2 + O2, CHBr2 + NO (both pressure-dependent), and CHBr2O2 + NO (k(2a) = (1.74 +/- 0.16) x 10(-11) cm3 molecule(-1) s(-1) at 23 degrees C). By measuring the amplitude of the secondary Br signal compared to the primary Br formed in the initial photolysis, it is established that the CHBr2O radical spontaneously decomposes to form CHBrO + Br at least 90%, and probably 100%, of the time, in agreement with previous work and with recent ab initio calculations. A survey of four other polybrominated methanes, CH2Br2, CHClBr2, CF2Br2, and CBr4, shows that they all generate secondary Br atoms when photolyzed at 266 nm in the presence of O2 and NO, suggesting that their reaction sequences are similar to that of bromoform.     

High temperature study of the reactions of O and OH with NH3

Mixtures of NH₃ and N₂O dilute in Ar were heated behind incident shock waves in the temperature range 1750–2060 K. A cw ring dye laser, tuned to the center of an OH absorption line in the ultraviolet, was used to monitor OH concentration profiles by absorption spectroscopy. Infrared emission was used to follow N₂O (at 4.5 μm) and NH₃ (at 10.5 μm) concentration—time histories. The early-time NH₃ and OH concentration profiles were sensitive to the rate constants of the reactions leading to the following best-fit expressions for k₂ and k₃:k₂ = 10^13.34±0.3 exp(?4470/T) and k₃ = 10^13.91±0.2 exp(-4230/T) cm³ mol^?1 s^?1. The results of this study combined with previous low-temperature data suggest a significant non-Arrhenius behavior for both k₂ and k₃.     

A shock tube study of the reaction NH2 + CH4 → NH3 + CH3 and comparison with transition state theory

The rate coefficient for NH₂ + CH₄ → NH₃ + CH₃ (R1) has been measured in a shock tube in the temperature range 1591–2084 K using FM spectroscopy to monitor NH₂ radicals. The measurements are combined with a calculation of the potential energy surface and canonical transition state theory with WKB tunneling to obtain an expression for k₁ = 1.47 × 10³ T ^3.01 e^?5001/T(K) cm³ mol^?1 s^?1 that describes available data in the temperature range 300 –2100 K. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 304–309, 2003     

Ionization gauge sensitivities of N2, O2, N2O,NO, NO2, NH3, CClF3 and CH3OH

A Bayard-Alpert (BA) gauge was used to determine apparent relative sensitivites S_rel,X for O₂, N₂O, NO, NO₂, NH₃, CClF₃ and CH₃OH from gauge calibration measurements in the range 1.3×10^?1 Pa≤p≤1.3·10^?3Pa. Nitrogen was used as a calibration standard.     

A shock tube study of methyl-methyl reactions between 1200 and 2400 K

The methyl-methyl reaction was studied in a shock tube using uv narrowline laser absorption to measure time-varying concentration profiles of CH₃. Methyl radicals were rapidly formed initially by pyrolysis of various precursors, azomethane, ethane, or methyl iodide, dilute in argon. The contributions of the various product channels, C₂H₆, C₂H₅ + H, C₂H₄ + H₂, and CH₂ + CH₄, were examined by varying reactant mixtures and temperature. The measured rate coefficients for recombination to C₂H₆ between 1200 and 1800 K are accurately fit using the unimolecular rate coefficients reported by Wagner and Wardlaw (1988). The rate coefficient for the C₂H₅ + H channel was found to be 2.4 (±0.5) × 10¹³ exp(?6480/T) [cm³/mol-s] between 1570 and 1780 K, and is in agreement with the value reported by Frank and Braun-Unkhoff (1988). No evidence of a contribution by the C₂H₄ + H₂ channel was found in ethane/methane/argon mixtures, although methyl profiles in these mixtures should be particularly sensitive to this channel. An upper limit of approximately 10¹¹ [cm³/mol-s] over the range 1700 to 2200 K was inferred for the rate coefficient of the C₂H₄ + H₂ channel. Between 1800 and 2200 K, methyl radicals are also rapidly removed by CH₃ + H ? ¹CH₂ + H₂. In this temperature range, the reverse reaction was found to have a rate coefficient of 1.3 (±0.3) × 10¹⁴ [cm³/mol-s], which is 1.8 times the room-temperature value. © 1995 John Wiley & Sons, Inc.