摘要:

AbstractThe isomerization and thermal decomposition of chloromethylacetylene (CMA) has been studied with two shock tube techniques. The first experiment (Jerusalem) utilizes single‐pulse shock tube methods to measure the isomerization rate of CMA to chloroallene. In addition, equilibrium constants can be estimated at ∼1200 K. The second experiment (Argonne) monitors Cl‐atom formation at temperatures above ∼1150 K. Absolute yield measurements have been performed over the 1200–1700 K range and indicate that two decomposition channels contribute to CMA destruction, namely, Cl fission and HCl elimination. The results show that the branching fraction between processes is temperature dependent. Therefore, direct Cl‐atom fission is accompanied by molecular elimination, undoubtedly giving HCl and one or more isomers of C3H2.MP2 6–31G(d,p) ab initio electronic structure calculations have been used to determine vibration frequencies and moments of inertia for three C3H3Cl isomers. Using these quantities, the experimental equilibrium constants required that ΔH00(CH2Cl–C≡CH ⇌ CHCl=C=CH2) = −;0.24 kcal mole−1. A potential energy surface pertinent to the present system has been constructed, and RRKM calculations have been carried out in order to explain the isomerization rates. The isomerization data can be explained withE0= 52.3 kcal mole−1and 〈ΔEdown〉 = 225 cm−1. Subsequent semi‐empirical Troe and RRKM‐Gorin modeling of the Cl atom rate data requireE0= (67.5 ± 0.5) kcal mole−1with a 〈ΔEdown〉 = (365 ± 90) cm−1. This suggests a heat of formation fo

ISSN:0021-2148    

DOI:10.1002/ijch.199600032

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThis study has examined the stereochemistry of the decomposition at 900–1000 K in a single‐pulse shock tube of 1‐vinyl‐2,3‐cis‐dideuteriocyclobutane to ethylenes and buta‐1,3‐dienes. The deuterated ethylenes formed during the decomposition, CHDCH2, (E)‐CHDCHD, and (Z)‐CHDCHD, were quantified via two independent techniques, FTIR and IR absorption spectroscopy using a tunable diode laser spectrometer. The results of both analyses indicated that equal amounts of (E)‐CHDCHD and (Z)‐CHDCHD were formed from the cis‐labeled reactant. In an earlier shock tube study of the decomposition at 1000–1200 K of two deuterium‐labeled cyclohexenes to ethylenes plus buta‐1,3‐dienes, a pathway via a vinylcyclobutane intermediate was implicated in a significant fraction of the decomposition events; the measured ratios of (E)‐CHDCHD to (Z)‐CHDCHD in that study were consistent with a complex mechanistic model in which the stereochemistry of deuterium labels in the cyclohexene reactant was lost in ethylene products formed via vinylcyclobutane. The presen

ISSN:0021-2148    

DOI:10.1002/ijch.199600033

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe pyrolysis of 3‐picoline dilute in argon was investigated using a single‐pulse shock tube over the temperature range of 1400–1650 K and total pressures of 12–13 atm. The principal products observed were HCN, acetylene, benzene, cyanoacetylene, methane, and pyridine. Assuming that 3‐picoline decomposes according to first‐order kinetics, the rate constant for its overall disappearance was determined to bekdis= 1016.9 (±0.8)exp[–99 (±6) kcal mol−1/RT] s−1. The principal initial decomposition routes were found to be via the formation of the 3‐picolyl andm‐pyridyl radicals whose subsequent ring‐opening led to the observed products. A 68‐step kinetic model was developed that successfully fits the experimental data. The dominant reactions, i.e., the formation of picolyl and pyridyl radicals and their subsequent chain‐opening reactions, were studied using ab initio quantum chemical techniques. The ab initio data were also incorporated into the kinetic model in the form of energies and A‐factors for reactions for which no kinetic or thermochemical data were previously available. Optimization of the kinetic model yields a value of 64 ± (3) kcal mol−1for the heat of formation of 3‐picolyl, a value lower than that for 2‐picolyl, suggesting that the decomposition of 3‐picoline more closely resembles that of to

ISSN:0021-2148    

DOI:10.1002/ijch.199600034

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe thermal decomposition of cyclobutanol has been investigated behind incident and reflected shock waves at temperatures between 950 K and 1450 K in the total density region (1.5 × 10−6– 1.5 × 10−5) mol/cm3. A strong absorption by an intermediate was observed at the wavelength of 193 nm. By comparing the kinetics with that of pyruvic acid, this absorption was identified to be that of vinyl alcohol. The kinetic parameters of vinyl alcohol, both for the production and the decomposition, were determined. The production rate constant was in agreement with that obtained by Back (Can J. Chem.1982,60, 2357), who monitored the ethylene production. The total decomposition mechanism of cyclobutanol was discussed on the basis of MO calculations. It was shown that vinyl alcohol was produced through a biradical before it isomerized to aceta

ISSN:0021-2148    

DOI:10.1002/ijch.199600035

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe thermal isomerization of azulene was studied behind reflected shocks in a pressurized driver single‐pulse shock tube. The temperature range covered was 1050–1400 K at overall densities of ∼2.5 × 10−5mol/cm3. The main reaction of azulene under these conditions is a unimolecular isomerization to naphthalene, but it also isomerizes, although at a much lower rate, to another isomer. The suggested “tetracyclic triene” intermediate structure for the azulene‐naphthalene isomerization can lead also to transition states that can describe isomerizations to 1‐methylene‐1H‐indene and 1, 2,3‐metheno‐1H‐indene,2,3‐dihydro. Small quantities of C2H2, C4H2, C6H6, and C6H5‐C≡CH were also found in the post‐shock samples, particularly at high temperatures. The Arrhenius parameters of the two high pressure limit rate constants for the isomerization processes are:azulene → naphthalene,k1= 1012.93exp(–62.8 × 103/RT) s−1azulene → second isomer,k2= 1012.42exp(–69.5 × 103/RT) s−1A discussion of the mechanis

ISSN:0021-2148    

DOI:10.1002/ijch.199600036

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractRates of hydrogen atom attack ono‐fluorotoluene (o‐FTOL) andm‐fluorotoluene (m‐FTOL) at temperatures of 988–1144 K and pressures of 2–2.5 bar have been determined in a single‐pulse shock tube study. Hydrogen atoms, generated from the decomposition of hexamethylethane, were allowed to react with the substrates and the characteristic products observed. Rate constants for two reaction channels, displacement of fluorine or methyl, were determined relative to displacement of methyl from 1, 3,5‐trimethylbenzene (135TMB). Evidence is presented that abstraction of F is unimportant over the studied temperature range. Withk(H + 135TMB →m‐xylene + CH3) = 6.7 × 1013exp(–3255/T) cm3mol−1s−1, the following rate expressions have been derived:k(H +o‐FTOL → C6H5CH3+ F) = 8.38 × 1013exp(–6041/T) cm3mol−1s−1; (1012–1142 K)k(H +o‐FTOL → C6H5F + CH3) = 2.37 × 1013exp(–2938/T) cm3mol−1s−1; (988–1142 K)k(H +m‐FTOL → C6H5CH3+ F) = 1.33 × 1014exp(–6810/T) cm3mol−1s−1; (1046–1144 K)k(H +m‐FTOL → C6H5F + CH3) = 2.04 × 1013exp(–3104/T) cm3mol−1s−1; (1008–1144 K)Uncertainties in the relative rate constants are estimated to be factors of about 1.1, while the above absolute values have estimated expanded uncertainties of about a factor of 1.4 in rate, 10 kJ mol−1in the activation energy, and a factor of 3 in the A‐factor. The present data are compared with relevant literature data. From our data and the thermochemistry, a model of the elementary steps comprising displacement of F is developed. On the basis of the model fit to our data, rate constants for the addition of atomic fluorine to toluene at 1100 K are derived. Rate expressions for fluorination reactions of toluene are also determined. The significance of the present results is discussed in

ISSN:0021-2148    

DOI:10.1002/ijch.199600037

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe thermal decomposition of cyclopentadiene has been studied in the temperature range 1260–1530 K behind reflected shocks. The total pressure ranged from 1.5 to 2.3 bar. Resonance absorption was used to record the temporal concentration profiles of H atoms. This sensitive technique allowed the study of the reaction systems under favorable conditions by applying very low initial concentrations (0.5–8 ppm). For cyclopentadiene decomposition R1, C5H6→ C5H3‐c + H, a rate expression ofk1= 1.1 × 1015exp(–38760/T) s−1was deduced. In a separate series of experiments the consumption by cyclopentadiene of H atoms, which had been generated by the thermal decay of ethyl iodide, was investigated. A preliminary value ofk2= 1.4 × 1014exp(–2739/T) cm3mol−1s−1was deduced for the total rate of H‐atom consumption by cyclopentadiene R

ISSN:0021-2148    

DOI:10.1002/ijch.199600038

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractReactions of H atoms with COS, CS2, and H2S were studied behind reflected shock waves at temperatures between 1170 K and 1830 K and pressures around 1.0 bar by applying atomic resonance absorption spectroscopy (ARAS) for time‐resolved measurements of H atoms at Lα. The thermal decomposition of a few ppm ethyl iodide (C2H5I) was used as a H‐atom source. In the presence of a large excess of the molecular reactant COS, CS2, or H2S, a consumption of H was observed which follows a pseudo first‐order rate law. Rate coefficients for the reactions:were determined to be:k1= 2.4 × 1014exp(–3415 K/T) cm3mol−1s−1k2= 1.4 × 1015exp(–9250 K/T) cm3mol−1s−1k3= 2.5 × 1014exp(

ISSN:0021-2148    

DOI:10.1002/ijch.199600039

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe reaction of silane with atomic oxygen (3P) was investigated by the shock‐tube–laser‐photolysis method over the temperature range of 900–1170 K. Oxygen atoms were produced by the ArF laser photolysis of SO2behind reflected shock waves and monitored with atomic resonance absorption spectroscopy. The rate constant for the SiH4+ O reaction was evaluated by taking the possible contribution of the consecutive reaction into consideration. The Arrhenius temperature coefficient was determined to beEa= 26.6 kJ mol−1, which is much higher than the experimental activation energies obtained at lower temperatures. Rate constants calculated by a transition state theory with the reaction barrier height ofE0= 10.2 kJ mol−1agreed well with both the present and the previous experimental results for a wide temper

ISSN:0021-2148    

DOI:10.1002/ijch.199600040

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractSilane and disilane diluted in argon and hydrogen mixtures were pyrolyzed behind incident shock waves at temperatures ranging from 900 to 2000 K, pressures from 0.2 to 0.7 atm, and total concentration from 3 × 1016to 1 × 1017silicon atoms per cm3. Formation of silicon particles was monitored by the attenuation of laser beams of two different wavelengths, thereby determining particle size, number density, and fractional yield. The conversion of silane and disilane into silicon particles exhibited a pronounced maximum at about 1150 K, which was found to be affected by reaction pressure, initial reactant concentration, and addition of hydrogen. Selected silicon particle samples were examined by electron diffraction, transmission electron microscopy, and secondary ion mass spectrometry. The results indicated that the produced particles were spherical, ranging from 100 to 400 Å in diameter, loosely agglomerated, and contained about 15% hydrogen on an atomic basis. A detailed chemical kinetic model was developed that describes gas‐phase pyrolysis of the parent molecule and homogeneous nucleation of silicon particles by 117 elementary reactions of 42 chemical species, and coagulation of the forming particles and their growth by gas‐surface deposition reactions with a method of moments. The model predictions were found to be extremely sensitive to the values of optical constants assigned to the silicon particle ma

ISSN:0021-2148    

DOI:10.1002/ijch.199600041

出版商:WILEY‐VCH Verlag    

年代:1996

数据来源: WILEY