摘要:

AbstractMeasurements from previous studies have shown that when hydroxyl radicals react with various chlorinated hydrocarbons under atmospheric conditions, free chlorine atoms can be produced. In one such study (Edney et al., [3]) from an analysis of the rate equations under a strict set of assumptions, Cl‐atom yields could be inferred. Since the approach was indirect, a more direct method for obtaining these yields has been developed. The technique described in this study involves scavenging Cl atoms produced by the reaction (using ethylene or propylene as the scavenger) and then measuring the yield of the stable chlorinated product generated. Cl‐atom yields were determined for allyl chloride, vinyl chloride, vinylidene chloride, trichloroethylene, and benzyl chloride. The experiments were performed by irradiating mixtures of CH3ONO/NO/chlorinated hydrocarbon/alkene in air in 150‐L Teflon chambers. The yields for the reaction of Cl atoms with the alkenes generating the stable products were determined in seperate experiments. Yields for the formation of Cl atoms upon reaction with hydroxyl radicals are as follows (with 1 σ deviation): allyl chloride: 0.37 ± 0.10, vinyl chloride: 0.04 ± 0.01, vinylidene chloride: 0.23 ± 0.09, trichloroethylene: 0.63 ± 0.34, and benzyl chloride: 0

ISSN:0538-8066    

DOI:10.1002/kin.550211002

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractGeneralized models for steady state catalytic processes are presented in matrix form. Multistep reaction rate control is assumed. Numerical algorithms for solving of the created linear and nonlinear equation systems are developed and tested. Four examples are considered: an Eley–Rideal‐mechanism, a Langmuir–Hinshelwood mechanism, a dual route, dual site mechanism, and a monomolecular decomposition with steady state multiplicity. The overall reaction rates are simulated as a function of the reactant concentrations.A maximum reaction rate is obtained in the case of a Langmuir–Hinshelwood mechanism (example 2), the location of the rate maximum in the concentration domain is shifted towards the concentration of the reactant with the lowest adsorption constants. An Eley–Rideal mechanism (example 1) has always monotonously increasing rate curves. In the case of steady state multiplicity (example 4) all steady states could be simulated with the proposed algorithm. The computation of reaction rate surfaces is important in investigating the behavior of complicated catalytic systems (e.g., systems with multistep rate control and/or steady state multiplicity), in planning of experiments and in chemical reactor s

ISSN:0538-8066    

DOI:10.1002/kin.550211003

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractThe thermochemical kinetics formulation of conventional transition state theory for bimolecular reactions allows for a separate contribution from each degree of freedom (translation, rotation, vibration, etc.) in the activated complex to the entropy and heat capacity of activation, and thus to the preexponential terms in the Arrhenius rate expression,k = ATnexp(−B/T). The number of vibrations and (possibly hindred) internal rotations varies depending on the nature of the reaction: atom + diatom, diatom + linear polyatom, etc. The temperature exponentncan be evaluated explicitly for each type of reaction if the harmonic oscillator‐rigid free rotor approximation is valid for the reagents and activated complex and if the contribution from tunneling is small. Various reaction types are examined successively, andnis evaluated for each case. The possible contributions of other factors (vibrational anharmonicity, hindered internal rotation, tunneling, “looseness” of activated complex) to the value ofnare also con

ISSN:0538-8066    

DOI:10.1002/kin.550211004

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractSingle‐channel hindered Gorin model RRKM calculations were performed on reaction (1).Good agreement between theory and experiment was obtained for the temperature and pressure dependence of reaction (1). Isotopic data for the reverse association reaction, (−1), reported previously, are consistent with the model. Rate constants were cast in the form of an analytical expression and appropriate parameters were tabula

ISSN:0538-8066    

DOI:10.1002/kin.550211005

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractThe kinetics of acetylene polymerization initiated by neopentane (Np) or acetone (Ac) decompositions has been investigated in a static reactor dynamically coupled to a modulated beam mass spectrometer between 850–950 K. Overall rates follow the expression:R= −d[C2H2]/dt=ks[X]1/2[C2H2] +ku[C2H2]2(I), whereXrepresents Np or Ac andks,kuthe rate constants of the sensitized and unsensitized reactions, respectively. The rate law of the sensitized reaction clearly suggests a chain polymerization mechanism withks=kp(ki/kt)1/2(i,t, andpstand for initiation, termination, and propagation, respectively). Remarkably, the derived values ofkpare nearly independent of the sensitizer, although Ac acts as a source of methyl radicals whereas Np also produces hydrogen atoms, and fall in the expected range for the addition of vinylic radicals to acetylene. It is shown that a chain transfer process involving the fast [1,5] intramolecular hydrogen atom shift in 4‐methyl‐buta‐1,3‐dien‐1‐yl radicals (CH3CH  CHCH ĊH) followed by further addition to C2H2and aromatization, transforms methyl radicals into hydrogen atoms and is able to account for the presence of toluene among the products of the sensitized reactions. Based on current thermochemical data for the but‐1‐en‐3‐yn‐2‐yl radical (CH2ĊCCH) and present rates of propagation it is argued that if the unsensitized polymerization of acetylene also proceeded by a vinyl radical chain, then even the most favorable self‐initiation reaction: 2C2H2= C4H3+ H (a), would be far too slow. Finally, present results also show that acetone at impurity levels (⩽ 0.1%) can not provide fast enough spurious initiation rates in chain mechanisms for the “unsensitize

ISSN:0538-8066    

DOI:10.1002/kin.550211006

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractThe transient diaryl disulfide radical anions (RSSR−) were produced in nonaqueous solutions at room temperature by the flash photolysis of a solution of arylthiolate ion pair in the presence of the excess corresponding disulfide. The transient spectra were almost identical with those obtained from γ‐radiolysis of the disulfides in 77 K 2‐methyl‐tetrahydrofuran (MTHF) glassy matrix. The spectra of disulfide radical anions in nonaqueous solutions were changed by cations, solvents, andpara‐substituents depending on the ion pair properties. The tighter ion pairs showed a shift of absorption band to the shorter wavelength. The disulfide radical anions decay by a unimolecular dissociation reaction to yield thiolate anion and thiyl radical. The decay kinetics were first‐order in the initial time region. The rate constants obtained were changed by the counter cations in the order Na+>K+>Cs+>Li+, and by solvents. The tighter ion pairs of the disulfide radical anions showed faster dissociation reaction. This is due to stabilization of a transition state with the co

ISSN:0538-8066    

DOI:10.1002/kin.550211007

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractSelectivity–reactivity correlations are shown to support a biradical pathway for the gas phase thermal Diels–Alder reactions of cyclohexa‐1,3‐diene with substituted ethenes except for those involving a carbony

ISSN:0538-8066    

DOI:10.1002/kin.550211008

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY

ISSN:0538-8066    

DOI:10.1002/kin.550211001

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY