摘要:

AbstractA sensitivity/uncertainty analysis is performed on a mechanism describing the chemistry of the polluted troposphere. General features of the photochemical reaction system are outlined together with an assessment of the uncertainties associated with the formulations of mechanistic details and rate data. The combined effects of sensitivity and uncertainty are determined using the Fourier amplitude sensitivity test (FAST) method. The results of this analysis identify the key parameters influencing the chemistry of NO2, O3, and PAN. Based on these findings, a series of recommendations are made for future experimental kinetic studies.

ISSN:0538-8066    

DOI:10.1002/kin.550111102

出版商:John Wiley&Sons, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractThe structure oft‐Bu3SiċH2, (I), suggested that it might be a persistent primary alkyl radical since it has (i) a bulky group to protect the radical center; (ii) no β‐hydrogens, so that a radical‐radical disproportionation reaction is impossible; (iii) a β‐silicon atom, which should prevent β‐scission oftert‐butyl as a unimolecular decomposition pathway. However, the self‐reaction of (I) in isooctane was found to be a diffusion controlled process with log(A/M−1sec−1) = 10.7 ± 0.3 andE= 2.5 ± 0.2 kcal mole−1. Hence (I) is not persistent and it is concluded that a persistent primary alkyl will only be observed when the—ĊH2moiety is deeply buried among

ISSN:0538-8066    

DOI:10.1002/kin.550111103

出版商:John Wiley&Sons, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractThe homogeneous gas‐phase decomposition kinetics of silane has been investigated using the single‐pulse shock tube comparative rate technique (T= 1035–1184˚K,Ptotal≈︁ 4000 Torr). The initial reaction of the decomposition SiH4\documentclass{article}\pagestyle{empty}\begin{document}$ {\rm SiH}_{\rm 4} \mathop \to \limits^1 {\rm SiH}_{\rm 2} + {\rm H}_{\rm 2} $\end{document}SiH2+ H2is a unimolecular process in its pressure fall‐off regime with experimental Arrhenius parameters of logk1(sec−1) = 13.33 ± 0.28–52,700 ± 1400/2.303RT. The decomposition has also been studied at lower temperatures by conventional methods. The results confirm the total pressure effect, indicate a small but not negligible extent of induced reaction, and show that the decomposition is first order in silane at constant total pressures. RRKM‐pressure fall‐off calculations for four different transition‐state models are reported, and good agreement with all the data is obtained with a model whose high‐pressure parameters are logA1(sec−1) = 15.5,E1(∞)= 56.9 kcal, and ΔE0±0(1) = 55.9 kcal. The mechanism of the decomposition is discussed, and it is concluded that hydrogen atoms are not involved. It is further suggested that silylene in the pure silane pyrolysis ultimately reacts with itself to give hydrogen: 2SiH2→ (Si2H4)* → (SiH3SiH)* → Si2H2+ H2. The mechanism of H ⟷ D exchange absorbed in the pyrolysis of Si

ISSN:0538-8066    

DOI:10.1002/kin.550111104

出版商:John Wiley&Sons, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractBy allowing dimethyl peroxide (10−4M) to decompose in the presence of nitric oxide (4.5 × 10−5M), nitrogen dioxide (6.5 × 10−5M) and carbon tetrafluoride (500 Torr), it has been shown that the ratiok2/k2′= 2.03 ± 0.47: CH3O + NO → CH3ONO (reaction 2) and CH3O + NO2→ CH3ONO2(reaction 2′). Deviations from this value in this and previous work is ascribed to the pressure dependence of both these reactions and heterogeneity in reaction (2). In contrast no heterogeneous effects were found for reaction (2′) making it an ideal reference reaction for studying other reactions of the methoxy radical. We conclude that the ratiok2/k2′is independent of temperature and fromk1= 1010.2±0.4M−1sec−1we calculate thatk2′= 109.9±0.4M−1sec−1. Bothk2andk2′are pressure dependent but have reached their limiting high‐pressure values in the presence of 500 Torr of carbon tetrafluoride. Preliminary results show thatk4= 10.9.0±0.610−4.5±1.1/ΘM−1sec−1(Θ = 2.303RTkcal mole−1) and byk4= 108.6±0.610−2.4±1.1/ΘM−1sec−1: CH3O + O2→ CH2O + HO2(

ISSN:0538-8066    

DOI:10.1002/kin.550111105

出版商:John Wiley&Sons, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractLinear free‐energy (LFE) correlations for gas phase O(3P) and OH addition and abstraction reactions with a number of organic compounds have been established using existing room‐temperature rate constants evaluated from the literature. Addition reaction rate constant correlations with ionization potential and abstraction reaction rate constant correlations with bond dissociation energies are examined and compared to the LFE approach. Using multiple regression analysis, empirical linear equations are derived and used to predict rate constants for reactions of O(3P) and OH with a number of organic molecules. The use of LFE room‐temperature rate predictions permits chemical modeling efforts to be extended to compounds where experimental determinations of rate coefficients are lacking and also serves as a useful tool in evaluation of experimental rate measure

ISSN:0538-8066    

DOI:10.1002/kin.550111106

出版商:John Wiley&Sons, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractIntrinsic spectral and kinetic parameters have been measured for the ethylperoxy radical, which was formed in the gas phase by the flash photolysis of azoethane in the presence of an adequate excess of oxygen. Absolute values of the extinction coefficient ϵ(λ) were derived from complementary measurements of the yield of nitrogen and the absorbance of an equivalent concentration of ethylperoxy radicals. The absorption spectrum is broad, structureless and comparatively weak; ϵ(236) = 1.02 × 103liter mole−1cm−1at the maximum, and the oscillator strength is 3.4 × 10−2. This spectrum resembles the spectrum of the methylperoxy radical closely in form, but it is less intense; the ratio of the values of oscillator strength is 0.5. The bimolecular reactions of mutual interaction of ethylperoxy radicals are not exclusively terminating, and ethoxy and hydroperoxy radicals are formed in kinetically significant quantities. A computer program was designed to simulate the rise and fall of the concentration of each radical species, and to perform the related kinetic analysis. This program predicted that a second‐order plot of the decline of the absorbance of the ethylperoxy radical during the dark period would not show a significant departure from linearity, a conclusion which was confirmed by experiment. Accordingly, the gradient of each such plot yielded a value ofk'/ϵ(λ), wherek' is the apparent value of the rate constant for the collective reactions of mutual interaction. This rate constant was evaluated from the product of corresponding values ofk'/ϵ(λ) and ϵ(λ); individual values are independent of the wavelength of measurement, and the mean value isk' = (6.6 ± 0.5) × 107liter mole−1sec−1. Further kinetic analysis yielded the corresponding absolute value:k= (6.0 ± 0.6) × 107liter mole−1sec−1. This value fits the pattern of a relationship between rate constant and structure shown by the methylperoxy, isopropylperoxy, andtert‐butylperoxy radicals. Adequate sensitivity for the characterization of the spectrum of the ethylperoxy radical was achieved by the use of a pulsed xenon arc as the monitoring light source in conjunction with a dual beam detection system with twin cells and balanced photomultipliers, and the

ISSN:0538-8066    

DOI:10.1002/kin.550111107

出版商:John Wiley&Sons, Inc.    

年代:1979

数据来源: WILEY

ISSN:0538-8066    

DOI:10.1002/kin.550111101

出版商:John Wiley&Sons, Inc.    

年代:1979

数据来源: WILEY