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1.
n-C3H7ONO was photolyzed with 366 nm radiation at ?26, ?3, 23, 55, 88, and 120°C in a static system in the presence of NO, O2, and N2. The quantum yields of C2H5CHO, C2H5ONO, and CH3CHO were measured as a function of reaction conditions. The primary photochemical act is and it proceeds with a quantum yield ?1 = 0.38 ± 0.04 independent of temperature. The n-C3H7O radicals can react with NO by two routes The n-C3H7O radical can decompose via or react with O2 via Values of k4/k2 ? k4b/k2 were determined to be (2.0 ± 0.2) × 1014, (3.1 ± 0.6) × 1014, and (1.4 ± 0.1) × 1015 molec/cm3 at 55, 88, and 120°C, respectively, at 150-torr total pressure of N2. Values of k6/k2 were determined from ?26 to 88°C. They fit the Arrhenius expression: For k2 ? 4.4 × 10?11 cm3/s, k6 becomes (2.9 ± 1.7) × 10?13 exp{?(879 ± 117)/T} cm3/s. The reaction scheme also provides k4b/k6 = 1.58 × 1018 molec/cm3 at 120°C and k8a/k8 = 0.56 ± 0.24 independent of temperature, where   相似文献   

2.
i-C4H9ONO was photolyzed with 366-nm radiation at ?8, 23, 55, 88, and 120°C in a static system in the presence of NO, O2, and N2. The quantum yield of i-C3H7CHO, Φ{i-C3H7CHO}, was measured as a function of reaction of reaction conditions. The primary photochemical act is and it proceeds with a quantum yield ?1 = 0.24 ± 0.02 independent of temperature. The i-C4H9O radicals can react with NO by two routes The i-C4H9O radical can decompose via or react with O2 via Values of k4/k2 ? k4b/k2 were determined to be (2.8 ± 0.6) × 1014, (1.7 ± 0.2) × 1015, and (3.5 ± 1.3) × 1015 molec/cm3 at 23 55, and 88°C, respectively, at 150-torr total pressure of N2. Values of k6/k2 were determined from ?8 to 120°C. They fit the Arrhenius expression: For k2 ? 4.4 × 1011 cm3/s, k6 becomes (3.2 ± 2.0) × 10?13 exp{?(836 ± 159)/T} cm3/s. The reaction scheme also provides k4b/k6 = 3.59 × 1018 and 5.17 × 1018 molec/cm3 at 55 and 88°C, respectively, and k8b/k8 = 0.66 ± 0.12 independent of temperature, where   相似文献   

3.
The reactions have been studied competitively over the range of 28–182°C by photolysis of mixtures of Cl2 + C2F5I+ CH4. We obtain where θ = 2.303RT J/mol. The use of published data on reaction (2) leads to log (k1cm3/mol sec) = (13.96 ± 0.2) ? (11,500 ± 2000)/θ.  相似文献   

4.
Vinyl and isopropyl radicals were generated by the pyrolysis of azoisopropane in the presence of acrolein at 473–563 K. Reaction products were analyzed by gas chromatography. Rate constant ratios k2/k1 = 0.02 ± 0.01 and k4/k3 = 0.01 ± 0.005 are suggested for the following reactions: The rate constant ratio of reactions (7) and (c) obeys the Arrhenius equation The Arrhenius equation was derived for (k8 + k9).  相似文献   

5.
The reaction of methyl radicals (Me) with hexafluoroacetone (HFA), generated from ditertiary butyl peroxide (dtBP), was studied over the temperature range of 402–433 K and the pressure range of 38–111 torr. The reaction resulted in the following displacement process taking place: where TFA refers to trifluoroacetone. The trifluoromethyl radicals that were generated abstract a hydrogen atom from the peroxide: such that k6a is given by: where θ = 2.303RT kcal/mol. The interaction of methyl and trifluoromethyl radicals results in the following steps: Product analysis shows that k17/kk = 2.0 ± 0.2 such that k17 = 1010.4±0.5M?1 · s?1. The rate constant k5 is given by: It is concluded that the preexponential factor for the addition of methyl radicals to ketones is lower than that for the addition of methyl radicals to olefins.  相似文献   

6.
Using the technique of molecular modulation spectrometry, we have measured directly the rate constants of several reactions involved in the oxidation of methyl radicals at room temperature: k1 is in the fall-off pressure regime at our experimental pressures (20–760 torr) where the order lies between second and third and we obtain an estimate for the second-orderlimit of (1.2 ± 0.6) × 10?12 cm3/molec · sec, together with third-order rate constants of (3.1 ± 0.8) × 10?31 cm6/molec2 · sec with N2 as third body and (1.5 ± 0.8) × 10?30 with neopentane; we cannot differentiate between k2a and k2c and we conclude k2a + (k2c) = (3.05 ± 0.8) × 10?13 cm3/molec · sec and k2b = (1.6 ± 0.4) × 10?13 cm3/molec · sec; k3 = (6.0 ± 1.0) × 10?11 cm3/molec · sec.  相似文献   

7.
A mixture of Br2 + HBr + C2F5I was photolyzed in the vapor phase. The reaction forms C2F5 radicals which are removed by Competitive studies over the range of 74–146°C gave ratios of k10/k9, and these were combined with values obtained previously by different methods at higher temperatures upto 515°C to give where θ = 2.303RT J/mol. A value is assigned to the activation energy E10, and this, with other data, leads to at 25°C. This result is in excellent agreement with two previous independent determinations.  相似文献   

8.
The abstraction of hydrogen and deuterium from 1,2-dichloroethane, 1,1,2-trichloroethane, and two of their deuterated analogs by photochemically generated ground state chlorine atoms has been investigatedin the temperature range 0–95°C using methane as a competitor. Rate constants and their temperature coefficients are reported for the following reactions Over the temperature range of this investigation an Arrhenius law temperature dependence was observed in all cases. Based on the adopted rate coefficient for the chlorination of methane [L.F. Keyser, J. Chem. Phys., 69 , 214 (1978)] which is commensurate with the present temperature range, the following rate constant values (cm3 s?1) are obtained: The observed pure primary, and mixed primary plus α- and β3-secondary kinetic isotope effects at 298 K are k3/k6 = 2.73 ± 0.08, and k1/k2 = 4.26 ± 0.12, respectively. Both show a normal temperature dependence decreasing to k3/k6 = 2.39 ± 0.06 and k1/k2 = 3.56 ± 0.09 at 370 K. Contrary to some simple theoretical expectations, the kinetic isotope effect for H/D abstraction decreases with increasing number of chlorine substituents in the geminal group in a parallel manner to the trend established previously for C1-substitution in the adjacent group. The occurrence of a β-secondary isotope effect, k4/k5, is established; this effect suggests a slight inverse temperature dependence.  相似文献   

9.
The reaction of iodine with allyl alcohol has been studied in a static system, following the absorption of visible light by iodine, in the temperature range 150-190°C and in the pressure range 10-200 torr. The rate-determining step has been found to be and k3 is consistent with the equation From the activation energy and the assumption E-3 = 1 ± 1 kcal mol?1, it has been calculated that kcal mol?1. The stabilization energy of the hydroxyallyl radical has been found to be 11.4 ± 2.2 kcal mol?1.  相似文献   

10.
Mixtures of cyanogen and nitrous oxide diluted in argon were shock-heated to measure the rate constants of A broad-band mercury lamp was used to measure CN in absorption at 388 nm [B2Σ+(v = 0) ← X2Σ+(v = 0)], and the spectral coincidence of a CO infrared absorption line [v(2 ← 1), J(37 ← 38)] with a CO laser line [v(6 → 5), J(15 → 16)] was exploited to monitor CO in absorption. The CO measurement established that reaction (3) produces CO in excited vibrational states. A computer fit of the experiments near 2000 K led to An additional measurement of NO via infrared absorption led to an estimate of the ratio k5/k6: with k5/k6 ? 103.36±0.27 at 2150 K. Mixtures of cyanogen and oxygen diluted in argon were shock heated to measure the rate constant of and the ratio k5/k6 by monitoring CN in absorption. We found near 2400 K: and The combined measurements of k5/k6 lead to k5/k6 ? 10?3.07 exp(+31,800/T) (±60%) for 2150 ≤ T ≤ 2400 K.  相似文献   

11.
The reactions of NH(X3Σ) with NO, O2, and O have been studied in reflected and incident shock wave experiments. The source of NH in all the experiments was the thermal dissociation of isocyanic acid, HNCO. Time-histories of the NH(X3Σ) and OH(X2Π) 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: were determined to be: and cm3 mol−1 s−1, where ƒ and F define the lower and upper uncertainty limits, respectively. The branching fraction of channel defined as k3b/k3total, was determined to be 0.19 ± 0.10 over the temperature range of 2940 K to 3040 K.  相似文献   

12.
The gas-phase photochlorination (λ = 436 nm) of the 1,1,1,2-C2H2Cl4 has been studied in the absence and the presence of oxygen at temperatures between 360 and 420°K. Activation energies have been estimated for the following reaction steps: The dissociation energy D(CCl3CHCl? O2) ± (24.8 ± 1.5) kcal/mole has also been estimated from the difference in activation energy of the direct and reverse reactions The mechanism is discussed and the rate parameters are compared to those obtained for a series of other chlorinated ethanes.  相似文献   

13.
The formation enthalpies were ascertained from the solution enthalpies in 2 n NaOH resp. 2 n NaOH + 1% H2O2. The results of equilibrium measurements in the systems give the formation enthalpies and standard entropies: . The value of the standard entropy of the gaseous MoOCl4 was estimated to be 91 (±3) cl. From the enthalpies and entropies of sublimation the values were obtained.  相似文献   

14.
Direct determinations of the rate constants (cm3/molec · sec) k1, k2, and k3 from 298 to 299°K are reported, using atomic resonance fluorescence in discharge flow systems:
  • 1 One standard deviation.
  • The rate constant k1, which has not been determined previously, was found to possess an insignificant temperature coefficient (EA = (0 ± 700) J/mole) in the range of 299 to 619°K. The present result for k2 agrees well with reinterpreted values from the one previous determination. Measurements of O atom consumption rates and Br atom production rates in the O + Br2 reaction are interpreted to give an estimate of the rate constant k4, which has not been reported previously, at 298°K: k3 has been measured at three temperatures between 299 and 602°K. The present and previous results for k3 were combined to give the following rate expression:   相似文献   

    15.
    H2S accelerates the thermal isomerization of cis-2-pentene (P2c) to 1-pentene (P1) and trans-2-pentene (P2t) to around 800 K. This effect is interpreted on the basis of a free radical mechanism in which 2-pentenyl and thiyl radicals are the main chain carriers. P1 formation is essentially explained by the competing processes: P2t formation is due to addition-elimination processes: the importance of which has been evaluated against process (?4μ): The following ratios of rate constants have been measured and are discussed: (RT in cal mol?1).  相似文献   

    16.
    Using published data on the kinetics of pyrolysis of C2Cl6 and estimated rate parameters for all the involved radical reactions, a mechanism is proposed which accounts quantitatively for all the observations: The steady-state rate law valid for after about 0.1% reaction is and the reaction is verified to proceed through the two parallel stages suggested earlier whose net reaction is A reported induction period obtained from pressure measurements used to follow the rate is shown to be compatible with the endothermicity of reaction A, giving rise to a self-cooling of the gaseous mixture and thus an overall pressure decrease. From the analysis, the bond dissociation energy DH0(C2Cl5? Cl) is found to be 70.3 ± 1 kcal/mol and ΔHf3000(·C2Cl5) = 7.7 ± 1 kcal/mol. The resulting π? bond energy in C2Cl4 is 52.5 ± 1 kcal/mol.  相似文献   

    17.
    On Chalcogenolates. 126. Studies on N-Cyanformamidino Dithiocarbimic Acid. 2. Thermal Behaviour of Potassium N-Cyanformamidino Dithiocarbimate in Solution The thermal treatment of K2[S2C?N? C(NH2)?N? CN] in methanolic solution yields . The semi-hydrate has been isolated. It reacts with acid to form The reaction with H3CI gives The compounds have been characterized by means of electron absorption, 1H- and 13C-N.M.R., infrared, and mass spectra.  相似文献   

    18.
    The kinetics of dimethyl sulfoxide (DMSO) oxidation by peroxomonophosphoric acid (PMPA) in aqueous medium at 308 K and I = 0.4 mol/dm3 follow the rate expressions In the pH range from 0 to 2, where k1 and k2 are 5.092 × 10?1 dm3/mol sec and ? 0, respectively; in the pH range from 4 to 7, where k2 = 8.127 × 10?3 and k3 = 2.90 × 10?3 dm3/mol sec; and in the pH range from 10 to 13.6, where k4 ? 0, and k5 = 3.08 × 10?2 dm3/mol sec. The reaction is interpreted in terms of mechanisms involving an electrophilic and a nucleophilic attack of the peroxomonophosphoric acid species, respectively, in acid and alkaline regions, on the sulfur atom of the sulfoxide molecule giving rise to S-type transition states followed by oxygen-oxygen bond fission to form the products.  相似文献   

    19.
    The reaction of CF3 radicals with H2O (D2O) has been studied over the range of 533–723 K using the photolysis and the pyrolysis of CF3I as the free radical source. Arrhenius parameters for the reactions where X = H or D, relative to CF3 radical recombination are given by where k/k is in cm3/2/mol1/2·s1/2 and θ = 2.303RT/cal/mol. The activation energy and the primary kinetic isotope effect have been compared with those derived from the BEBO method.  相似文献   

    20.
    The kinetics and mechanism of ascorbic acid (DH2) oxidation have been studied under anaerobic conditions in the presence of Cu2+ ions. At 10?4 ≤ [Cu2+]0 < 10?3M, 10?3 ≤ [DH2]0 < 10?2M, 10?2 ≤ [H2O2] ≤ 0.1M, 3 ≤ pH < 4, the following expression for the initial rate of ascorbic acid oxidation was obtained: where χ2 (25°C) = (6.5 ± 0.6) × 10?3 sec?1. The effective activation energy is E2 = 25 ± 1 kcal/mol. The chain mechanism of the reaction was established by addition of Cu+ acceptors (allyl alcohol and acetonitrile). The rate of the catalytic reaction is related to the rate of Cu+ initiation in the Cu2+ reaction with ascorbic acid by the expression where C is a function of pH and of H2O2 concentration. The rate equation where k1(25°C) = (5.3 ± 1) × 103M?1 sec?1 is true for the steady-state catalytic reaction. The Cu+ ion and a species, which undergoes acid–base and unimolecular conversions at the chain propagation step, are involved in quadratic chain termination. Ethanol and terbutanol do not affect the rate of the chain reaction at concentrations up to ≈0.3M. When the Cu2+–DH2–H2O2 system is irradiated with UV light (λ = 313 nm), the rate of ascorbic acid oxidation increases by the value of the rate of the photochemical reaction in the absence of the catalyst. Hydroxyl radicals are not formed during the interaction of Cu+ with H2O2, and the chain mechanism of catalytic oxidation of ascorbic acid is quantitatively described by the following scheme. Initiation: Propagation: Termination:   相似文献   

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