Temperature dependent rate constant for the reaction of H-atoms with carbonyl sulfide

The kinetics of the reaction of H-atom with carbonyl sulfide (OCS) has been investigated at nearly 2 Torr total pressure of helium over a wide temperature range, T = 255–960 K, using a low-pressure discharge flow reactor combined with an electron impact ionization quadrupole mass spectrometer. The rate constant of the reaction H + OCS → SH + CO (1) was determined under pseudo-first order conditions, monitoring the kinetics of H-atom consumption in excess of OCS, k₁ = 6.6 × 10⁻¹³ × (T/298)³ × exp(−1150/T) cm³ molecule⁻¹ s⁻¹ (with estimated total uncertainty on k₁ of 15% at all temperatures). Current measurements of k₁ at intermediate temperatures (520–960 K) appear to reconcile previous high and low temperature data and allow the above expression for k₁ to be recommended for use in the extended temperature range between 255 and 1830 K with a conservative uncertainty of 20%.     

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-dependent rate constants for the reactions of chlorine atom with methanol and Br2

Kinetics of the reaction of Cl atoms with methanol has been investigated at 2 Torr total pressure of helium and over a wide temperature range 225-950 K, using a discharge flow reactor combined with an electron impact ionization quadrupole mass spectrometer. The rate constant of the reaction Cl + CH₃OH → products (1) was determined using both absolute measurements under pseudo-first order conditions, monitoring the kinetics of Cl-atom consumption in excess of methanol and relative rate method, k₁ = (5.1 ± 0.8) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹, and was found to be temperature independent over the range T = 225-950 K. The rate constant of the reaction Cl + Br₂ → BrCl + Br (3) was measured in an absolute way monitoring Cl-atom decays in excess of Br₂: k₃ = 1.64 × 10⁻¹⁰ exp(34/T) cm³ molecule⁻¹ s⁻¹ at T = 225-960 K (with conservative 15% uncertainty). The experimental data for k₃ can also be adequately represented by the temperature independent value of k₃ = (1.8 ± 0.3) × 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹. The kinetic data from the present study are compared with previous measurements.     

三氯乙烷与氟原子的反应机理研究和速率常数计算

采用双水平直接动力学方法研究了反应CH3CCl3+F→CH2CCl3+HF的反应机理和动力学性质;在MPW1K/6-311+G(d,p)水平上优化了所有稳定点的几何构型,并通过频率分析进行了验证;随后在MCG3-MPWPW91//MPW1K水平上进行了能量校正,并利用变分过渡态理论,在MCG3-MPWPW91//MPW1K/6-311+G(d,p)水平上计算了反应在200～2 000K温度区间内的速率常数.结果表明,反应物CH3CCl3属于Cs点群,-CH3基团上的3个H原子等同,反应存在单个氢迁移反应通道.     

用直接动力学方法确定CF3CHFCF3与Cl原子反应的速率常数

采用直接动力学方法研究了CF3CHFCF3与氯原子反应的动力学特性,利用包含小曲率隧道效应的正则变分过渡态理论确定了200～2 000 K温度区间内反应的速率常数.     

ESR study of the 1,2-migration of F atoms in polyfluorinated radicals

The 1,2-migration of the F atom in polyfluorinated cyclohexadienyl radicals generated in the reaction of perfluoro-p-xylene with pentafluorobenzoyl peroxide has been observed directly by ESR.Translated fromIzvestiya Akademii Nauk. Seriya Khitnicheskaya, No. 1, pp. 100–103, January, 1995.     

Theoretical study on the reaction mechanism of (CH3)3CO(.) radical with NO

The reaction mechanism of (CH3)3CO(.) radical with NO is theoretically investigated at the B3LYP/6-31G* level. The results show that the reaction is multi-channel in the single state and triplet state. The potential energy surfaces of reaction paths in the single state are lower than that in the triple state. The balance reaction: (CH3)3CONO←→ (CH3)3CO(.)+NO, whose potential energy surface is the lowest in all the reaction paths, makes the probability of measuring (CH3)3CO(.) radical increase. So NO may be considered as a stabilizing reagent for the (CH3)3CO(.)radical.     

Kinetic study of the reaction of CH3O with Br and Br2

The title reactions have been studied at room temperature by applying the discharge flow method coupled with laser induced fluorescence detection of methoxy radicals and resonance fluorescence detection of bromine atoms. The following rate constants were determined: CH₃O + Br Õ products (1) k ₁ (298 K) = (3.4 ± 0.4 (1)) × 10¹³ cm³ mol^-1 s^-1, CH₃O + Br₂ Õ products (2) k ₂ (298 K) £ 5 × 10⁸ cm³ mol^-1 s^-1.     

The role of hydrogen atoms in CIDNP effects in the reaction of diisobutylaluminum hydride with CCl4

Integral polarization of chloroform, methylene dichloride, and pentachloroethane was observed in the¹H NMR spectra during the exothermal reaction of a 1M solution of Bu₂ ⁱ in 1,4-dioxane with CCI₄. CIDNP was shown to appear in the diffusion radical pair of the hydrogen atom and trichloromethyl radical. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2097–2099, October, 1998.     

Rate constant for the reaction of F-atoms with trichloroacetic acid

Kinetics of the reaction of F-atoms with trichloroacetic acid was studied at 293 K using a low-pressure flow reactor. Reactant concentrations were monitored by mass spectrometry combined with molecular beam sampling. The reaction rate constant obtained was k = (4.3 ± 0.8) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹. This is an average value determined by the relative method employing four reference reactions of F-atoms: with 1,1,1-trichloroethane, ethanol, cyclohexane, and 2-fluoroethanol, for which rate constant ratios k/k_ref = 7.4 ± 1.2, 0.24 ± 0.02, 0.28 ± 0.02, and 0.34 ± 0.04, respectively, were obtained. The resultant rate constant is compared with the rate constants for the related fluoro-substituted acids.     

Instanton rate constant calculations close to and above the crossover temperature

Canonical instanton theory is known to overestimate the rate constant close to a system‐dependent crossover temperature and is inapplicable above that temperature. We compare the accuracy of the reaction rate constants calculated using recent semi‐classical rate expressions to those from canonical instanton theory. We show that rate constants calculated purely from solving the stability matrix for the action in degrees of freedom orthogonal to the instanton path is not applicable at arbitrarily low temperatures and use two methods to overcome this. Furthermore, as a by‐product of the developed methods, we derive a simple correction to canonical instanton theory that can alleviate this known overestimation of rate constants close to the crossover temperature. The combined methods accurately reproduce the rate constants of the canonical theory along the whole temperature range without the spurious overestimation near the crossover temperature. We calculate and compare rate constants on three different reactions: H in the Müller–Brown potential, methylhydroxycarbene → acetaldehyde and H₂ + OH → H + H₂O. © 2017 Wiley Periodicals, Inc.     

Direct ab initio dynamics study of the reaction of C2(A3Πu) with CH4

The reaction of C₂(A³Π_u) with CH₄ has been investigated over a wide temperature range 200–3,000 K by direct ab initio dynamics method at the BMC‐CCSD//BB1K/6‐311+G(2d,2p) level of theory. The optimized geometries and frequencies of the stationary points are calculated at the BB1K/6‐311+G(2d,2p) level, and then the energy profiles of the reactions are refined using the BMC‐CCSD method. The activation barrier height for H‐abstraction reaction was calculated to be 4.44 kcal/mol in temperature range (337–605 K), and the electron transfer behavior was also analyzed by quasi‐restricted molecular orbital method in detail. The canonical variational transition‐state theory (CVT) with the small curvature tunneling (SCT) correction method is used to calculate the rate constants over a wide temperature range 200–3,000 K. The theoretical results shows that variational effect is to some extent large in lower temperature range, and small curvature and tunneling effect play important roles to the H‐atom abstraction only at lower temperatures. The CVT/SCT rate constants are in good agreement with the available experimental results. Our theoretical study is expected to provide a direct insight into the reaction mechanism and may be useful for estimating the kinetics of the title reaction over a wide temperature range where no experimental data are available so far. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Kinetics of the reaction of the TEMPO radical with alkylarenes

The kinetics of the reaction of the stable radical 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) with a series of alkylarenes containing primary and secondary benzyl C—H bonds was studied by ESR, and the reaction rate constants were determined. The scheme of the process under study was examined, and the applicability boundaries of the simplification during analysis were shown. The selectivities of TEMPO and the more reactive cumylperoxyl radical were compared.     

Measurements of the apparent rate constant for the reaction of iodine monoxide with chlorine monoxide to form iodine atoms

An apparatus for measuring the resonance fluorescence signals of iodine and chlorine atoms is constructed to study iodine monoxide reaction with chlorine monoxide. A technique using the reaction of chlorine atoms with C₂H₆ is developed to calibrate the sensitivity of the apparatus to chlorine atoms. The apparent rate constants for the reaction between 10^• and CIO^• radicals producing iodine atoms was measured at 295 K k_app = (2.62 ± 0.57) x 10-^-11 cm³ molecule^-1 s^-1.     

NO3自由基与HNO及HONO反应机理研究

有研究显示NO3自由基会在RDX热解过程中形成,然而实验中却始终未有发现.本文首次通过量子化学方法研究了NO3自由基分别与RDX两种热解产物HNO及HONO的反应,并利用CCSD(T)/6-311++G(d,p)方法对反应势垒进行了精确计算.计算结果显示,NO3+HNO反应为无势垒反应,且放出大量热量,预示该反应极易发生.这为NO3自由基始终没有在RDX热解实验中被观察到提供了一种解释.     

Reverse atom transfer radical polymerization of methyl methacrylate with a new catalytic system,FeCl3/isophthalic acid

A new catalytic system, FeCl₃/isophthalic acid, was successfully used in the reverse atom transfer radical polymerization (RATRP) of methyl methacrylate (MMA) in the presence of a conventional radical initiator, 2,2′‐azo‐bis‐isobutyrontrile. Well‐defined poly(methyl methacrylate) (PMMA) was synthesized in an N,N‐dimethylformamide solvent at 90–120 °C. The polymerization was controlled up to a molecular weight of 50,000, and the polydispersity index was 1.4. Chain extension was performed to confirm the living nature of the polymer. The kinetics of the RATRP of MMA with FeCl₃/isophthalic acid as the catalyst system was investigated. The apparent activation energy was 10.47 kcal/mol. The presence of the end chloride atom on the resulting PMMA was demonstrated by ¹H NMR spectroscopy. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 765–774, 2001     

Theoretical study and rate constant calculation for reaction of CF(3)CH(2)OH with OH

The reaction mechanism of CF(3)CH(2)OH with OH is investigated theoretically and the rate constants are calculated by direct dynamics method. The potential energy surface (PES) information, which is necessary for dynamics calculation, is obtained at the B3LYP/6-311G (d, p) level. The single-point energy calculations are performed at the MC-QCISD level using the B3LYP geometries. Complexes, with the energies being less than corresponding reactants and products, are found at the entrance and exit channels for methylene-H-abstraction channel, while for the hydroxyl-H-abstraction channel only entrance complex is located. By means of isodesmic reactions, the enthalpies of the formation for the species CF(3)CH(2)OH, CF(3)CHOH, and CF(3)CH(2)O are estimated at the MC-QCISD//B3LYP/6-311G (d, p) level of theory. The rate constants for two kinds of H-abstraction channels are evaluated by canonical variational transition state theory with the small-curvature tunneling correction (CVT/SCT) over a wide range of temperature 200-2000 K. The calculated results are in good agreement with the experimental values in the temperature region 250-430 K. The present results indicate that the two channels are competitive. Below 289 K, hydroxyl-H-abstraction channel has more contribution to the total rate constants than methylene-H-abstraction channel, while above 289 K, methylene-H-abstraction channel becomes more important and then becomes the major reaction channel.     

Kinetic regularities of the heat release during the reactions of aliphatic hydrocarbons with aqueous HNO3

The kinetics of the heat release during the reactions of aqueous HNO₃ withn-heptane andn-octadecane was studied. The kinetic regularities of the reactions of hydrocarbons C₇H₁₆−C₁₈H₃₈ with HNO₃ and the heats of the reactions were described. At all stages, except initial, the hydrocarbon reacts with NO₂ and nitric acid reproduces NO₂ in the reaction with NO. The accumulation of NO₂ results in the acceleration of the process. When the pressure of the hydrocarbon vapor is equilibrium, its reaction with NO₂ can also proceed in the gas phase. The contribution of this reaction to the total heat release was estimated. The additives of aromatic and unsaturated hydrocarbons to aliphatic hydrocarbons increase strongly the initial rate of the heat release and changes slightly the subsequent stages of the process. Naphthenic hydrocarbons have almost no effect on the kinetic parameters of the process. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 35–40, January, 1998.