摘要:

AbstractThe literature on the pyrolysis of acetylene below 1000 K is reviewed and it is shown that the reaction is a radical chain polymerization initiated by H atoms. The induction period is examined and shown to arise from a rapid autocatalysis produced by the very first product, vinyl acetylene. Data from studies of acetylene polymerization induced by vinyl acetylene and styrene are examined and shown to be in good qualitative agreement with the radical chain process presented. Measured and where needed, estimated rate constants are given to produce numerical estimates of chain length, rates of polymerization, induction period, and rates of initiation. It is further shown that all the products of the polymerization are capable of efficiently initiating chains in the system. An examination of the possible kinetics of vinylidene shows that it does not play any role in acetylene chemistry.

ISSN:0538-8066    

DOI:10.1002/kin.550240302

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe present study examines the kinetics and mechanism of the formation of [Zn(CN)4]2−from ZnR22−(R represents 4‐(2‐Pyridylazo)resorcinol, short named as Par) and vice versa. The reactions have been followed at 494 nm (λmaxof [Zn(Par)2]2−, ε = 7.8 × 104M−1cm−1) using stopped‐flow spectrophotometer in presence of excess of incoming ligand. The data show that the formation of [Zn(CN)4]2−complex is first order in [ZnR22−] and the order with respect to [CN−] varies from one at higher cyanide concentration to zero at low [CN−]. These observations suggest a slow dissociation of [ZnR2]2−to ZnR and R2−and a cyanide assisted rapid dissociation of [ZnR2]2−to [ZnR(CN)x]x−followed by their rapid conversion to [Zn(CN)4]2−. The reaction of Zn(Par) with cyanide ions also follow first order kinetics at higher as well as lower cyanide concentrations. The reverse reaction exhibits first order dependence each in [Zn(CN)42−] and [Par2−], but an inverse first order dependence in [CN−] at low Par concentrations. However, at higher Par concentration the reaction rate tends to be independent of [Par2−]. On the basis of forward and reverse rate studies, a five step mechanism consistent with these results has been proposed. The activation parameters and the effect of ionic strength have been used in further support to the proposed mechanism. The effect of pH on the rates of forward and

ISSN:0538-8066    

DOI:10.1002/kin.550240303

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe effect of CFCl3(0.025–0.200 mbar) addition on the formation of ozone in 214 nm photolysis of oxygen (800–2000 mbar) was investigated. Kinetic analysis of the drastic reduction in ozone formation in the presence of CFCl3shows that it proceeds by a chain mechanism with a chain length of 5.07 ± 0.21(2σ). This chain length is independent of CFCl3and O2pressures as well as incident light intensity and the mechanism of the chain reaction is governed by the Cl generating reactions of ClO radicals. A mechanism based only on the self reaction of these radicals: ClO + ClO → Cl2+ O2(7), Cl + ClO2(8), and Cl + OClO (9), followed by fast decomposition of ClO2into Cl and O2, predicts a chain length which is considerably lower than the observed value. Incorporation of the reaction CFCl2O2+ ClO → CFCl2O + ClO2(11) in the mechanism satisfactorily accounts for the observed chain length. A lower limit of 3 × 10−12cm3molecule−1s−1fo

ISSN:0538-8066    

DOI:10.1002/kin.550240304

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe reaction between H and C3H5has been studied at 291 K. Exciplex laser flash photolysis at 193.3 nm of hexa‐1,5‐diene‐He mixtures generated both H and C3H5([H] ≪ [C3H5]), which were detected in time‐resolved mode by resonance fluorescence and absorption spectroscopy, respectively. Rate coefficients are presented at four pressures in the range 98 ⩽P/torr ⩽ 400; no clear pressure‐dependence is found in this range of pressures and the mean rate coefficient is (2.8 ± 1.0) × 10−10cm3molecule−1s−1. Calculations based on the Troe factorization method confirm that this reaction is near its high‐pressure limit under th

ISSN:0538-8066    

DOI:10.1002/kin.550240305

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractReactions 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(X2Πi) 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:andwere determined from early‐time NH and OH formation rates, with least‐squares two‐parameter fits of the results given by:\documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{*{20}c} {k_{2a} = 1.9 \times 10^{13} \exp (-7150/T,{\rm K})} & {{\rm (}f = 0.62,{\rm F} = 1.52{\rm)}} & {T = 2120-2500{\rm K}}\end{array} $$\end{document}and\documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{*{20}c} {k_{2c} = 1.4 \times 10^{14} \exp (- 10300/T,{\rm K})} & {{\rm (}f = 0.65,{\rm F} = 1.35{\rm)}} & {T = 2120 - 3190{\rm K}},\end{array} $$\end{document}cm3mol−1s−1. The minimum and maximum rate constant factors (ƒ,F) define the lower and upper uncertainty limits, respectively.An upper limit on the rate coefficient ofwas determined to be:\documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{*{20}c} {k_3 \le 1.5 \times 10^{12} {\rm cm}^3 {\rm mol}^{- 1} {\rm s}^{- 1},} & {T = 2120 - 2350{\rm K}}\end{arr

ISSN:0538-8066    

DOI:10.1002/kin.550240306

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe rate coefficients of thermal decomposition of peroxyacetic nitric anhydride (PAN) and peroxymethacrylic nitric anhydride (MPAN) were measured over the temperature range 302–323 K. The resulting Arrhenius expressions werek= 1017.4±0.4exp(−28.5 ± 0.5/RT) for PAN, andk= 1016.2±0.7exp(−26.8 ± 1.0/RT) for MPAN, where the activation energy is in Kcal/mol. These results are in good agreement with previous studies of PAN and other PAN‐type compounds, and imply that energies of RC(O)OONO2bonds are relatively independent of th

ISSN:0538-8066    

DOI:10.1002/kin.550240307

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

ISSN:0538-8066    

DOI:10.1002/kin.550240301

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY