bluuebunny/crossref_metadata_2025 huggingface dataset:
Updated chemical mechanism for atmospheric photooxidation of toluene
Authors: Leone Joseph A. , Seinfeld John H.
Published: January 2005

A new reaction mechanism describing the atmospheric photochemical oxidation of toluene is formulated and tested against environmental chamber data from the University of California, Riverside, Statewide Air Pollution Research Center (SAPRC). On simulations of toluene—NOx and toluene—benzaldehyde—NOx irradiations, the average predicted O3 and PAN maxima are within 3% of the experimental values. Simulations performed with the new mechanism are used to investigate various mechanistic paths, and to gain insight into areas where our understanding is not complete. Specific areas that are investigated include benzaldehyde photolysis, organic nitrate formation, alternate ring fragmentation pathways, and conjugated γ‐dicarbonyl condensation to the aerosol phase.
Kinetics and mechanism of the reaction of aqueous sulfite with N‐chloroalanylalanylalanine
Authors: Stanbro William D. , Lenkevich Michael J.
Published: January 2005

The rate of the reaction of aqueous sulfite with the N‐chloropeptide N‐chloroalanylalanylalanine has been studied as a function of pH, temperature, and ionic strength. The results of this work suggest that the mechanism of the reaction involves the interaction of the neutral chloramine with the three ionic forms of sulfite, SO, HSO, and H2SO3, with the rate of reaction increasing rapidly with increasing protonation. The estimated second‐order rate constants for each ionic species as a function of temperature are

where the activation energies are in units of cal/mol.
Rate constants for the reactions of O3 and OH radicals with a series of alkynes
Authors: Atkinson Roger , Aschmann Sara M.
Published: January 2005

Rate constants for the reactions of O3 and OH radicals with acetylene, propyne, and 1‐butyne have been determined at room temperature. The rate constants obtained at 294 ± 2 K for the reactions of O3 with acetylene, propyne, and 1‐butyne were (7.8 ± 1.2) × 10−21 cm3/molecule · s, (1.43 ± 0.15) × 10−20 cm3/molecule · s, and (1.97 ± 0.26) × 10−20 cm3/molecule · s, respectively. The rate constants at 298 ± 2 K and atmospheric pressure for the reactions with the OH radical, relative to a rate constant for the reaction of OH radicals with cyclohexane of 7.57 × 10−12 cm3/molecule · s, were determined to be (8.8 ± 1.4) × 10−13 cm3/molecule · s, (6.21 ± 0.31) × 10−12 cm3/molecule · s, and (8.25 ± 0.23) × 10−12 cm3/molecule · s for acetylene, propyne, and 1‐butyne, respectively. These data are discussed and compared with the available literature rate constants.
Mechanism and kinetics of the shock‐tube decomposition of vinylsilane
Authors: Rickborn S. F. , Ring M. A. , O'Neal H. E. , Coffey D.
Published: January 2005

The shock‐induced thermal decompositions of vinylsilane and vinylsilane‐d3 (0.2% on argon) have been studied in the temperature range of 1085–1275 K, and at total pressures of about 3100 torr. In systems without silylene traps, some induced decomposition occurs which is attributed to the silylene chain sequence VSiH → C2H2 + SiH2, S̈iH2 + VSiH3 ⇄ VSiH2SiH3 → VSiH2S̈iH + H2, VSiH2S̈iH → VSiH + S̈iH2. In the presence of silylene traps (butadiene and acetylene), the overall decomposition kinetics are log k(VSiH3, s−1) = 14.95 − 63,268 cal/2.303RT and log k(VSiD3, s−1) = 15.14 − 64,815 cal/2.303RT. Three primary processes contribute to the decomposition: 1,1‐H2 elimination, 1,2‐H2 elimination, and ethylene elimination. Two mechanisms are proposed, one for exclusive primary process formation of C2H4, and the other for both primary and secondary formation routes. Modeling studies are reported which show that both mechanisms can be made compatible with the rate and product yield data within experimental errors.
Reaction of CF3 radicals with H2S
Authors: Arican Haluk , Arthur Neville L.
Published: January 2005

Hydrogen abstration from H2S by CF3 radicals, generated by the photolysis of both CF3COCF3 and CF3I, has been studied in the temperature range 314–434 K. The rate constant, based on the value of 1013.36 cm3/mol · s for the recombination of CF3 radicals, is given by

with CF3COCF3 as the radical source, and

with CF3I as the radical source, where k2 is in cm3/mol · s and E is in J/mol. These results resolve a previously existing controversy concerning the values of the rate constants for this reaction. They show that CF3 radicals are less reactive than CH3 radicals in attacking H2S, and this behavior indicates that polar effects play a significant role in the hydrogen transfer reactions of CF3 radicals.
Cyanogen pyrolysis and the CN + NO reaction behind incident shock waves
Authors: Colket M. B.
Published: January 2005

The reaction chemistry of C2N2Ar and C2N2NOAr mixtures has been investigated behind incident shock waves. Progress of the reaction was monitored by observing the cyano radical (CN) in absorption at 388.3 nm. A quantitative spectroscopic model was used to determine concentration histories of CN. From initial slopes of CN concentration during cyanogen pyrolysis, the rate constant for C2N2+ M → 2CN + M (1) was determined to bek1= (4.11 ± 1.8) × 1016exp(−47,070 ± 1400/T) cm3/mol · s. A reaction sequence for the C2N2NO system was developed, and CN profiles were computed. By comparison with experimental CN profiles the rate constant for the reaction CN + NO → NCO + N (3) was determined to bek3= 10(14.0 ± 0.3)exp(−21,190 ± 1500/T) cm3/mol · s. In addition, the rate of the four‐centered reaction CN + NO → N2+ CO (2) was estimated to be approximately three orders of magnitude below collision frequency.
The reactions of isotopically labeled N15NO+ with CO, NO, O2, N2, NO2, and N2O
Authors: Kemper Paul R. , Bowers M. T.
Published: January 2005

The reactions of labeled N15NO+ with CO, NO, O2, 18O2, N2, NO2, and N2O have been investigated using a tandem ICR instrument. In each case the total rate coefficient, product distribution, and kinetic energy dependence were measured. The results indicate that very specific reaction mechanisms govern these reactions. This conclusion is suggested by the lack of isotopic scrambling in many cases and by the complete absence of energetically allowed products in almost all of the systems. The kinetic energy studies indicate that most of the reaction channels proceed through an intermediate complex at low energies and via a direct mechanism at higher kinetic energies. Such direct mechanisms include long range charge transfer and atom or ion transfer.
Ebulliometric study of the decomposition of urea in aqueous media
Authors: de Azevedo Francisco G. , de Oliveira Walace A.
Published: January 2005

Boiling‐temperature measurements have been used to study the kinetics of the decomposition of urea. Values for the rate constants in neutral, acid, and basic media have been obtained and compared with literature data. The effect of the reverse reaction on the value of the experimental rate constants is discussed. The profile of the ebulliometric curves is different for the three media and is correlated with the number of various species present in solution. It is concluded that ebulliometric measurements can be useful for kinetic studies.
The reactions of S(3PJ) atoms with thiiranes
Authors: Van Roodselaar A. , Safarik I. , Strausz O. P.
Published: January 2005

The reactions of ground‐state S(3PJ) atoms with thiirane, methylthiirane, and trans‐2,3‐dimethylthiirane have been studied by flash photolysis‐VUV kinetic absorption spectroscopy. From the analysis of the S(3PJ) decay plots the following rate constants were determined: (1.4 ± 0.2) × 1013, (2.7 ± 0.3) × 1013 and (4.0 ± 0.2) × 1013 (in cm3 mol−1 s−1 units) for thiirane, methylthiirane and trans‐2,3‐dimethylthiirane, respectively, showing an upward trend with increasing methylation.
Basic hydrolysis of glyceryl nitrate esters. II. 1,2‐glyceryl and 1, 3‐glyceryl dinitrate esters
Authors: Capellos C. , Fisco W. J. , Ribaudo C. , Hogan V. D. , Campisi J. , Murphy F. X. , Castorina T. C. , Rosenblatt D. H.
Published: January 2005

Kinetics of the basic hydrolysis of 1,2‐glyceryl dinitrate (1,2‐DNG) and 1,3‐glyceryl dinitrate (1,3‐DNG) esters were investigated in CO2‐free aqueous calcium hydroxide solutions. The hydrolysis reactions were carried out in a temperature controlled reactor vessel with provision for continuous N2 sparging of the reaction mixture. Both glyceryl dinitrate esters hydrolyzed via second‐order reaction at 25°C. 1,2‐DNG in basic solutions isomerized to 1,3‐DNG which subsequently hydrolyzed to yield products. The main hydrolysis product of 1,3‐DNG was identified as glycidyl nitrate. Other products formed during the basic hydrolysis of DNGs were nitrites and nitrates.
Thermal decomposition of methyl nitrite in shock waves studied by laser probing
Authors: Hsu D. S. Y. , Burks G. L. , Beebe M. D. , Lin M. C.
Published: January 2005

The unimolecular decomposition of methyl nitrite in the temperature range 680–955 K and pressure range 0.64 to 2.0 atm has been studied in shock‐tube experiments employing real‐time absorption of CW CO laser radiation by the NO product. Computer kinetic modeling using a set of 23 reactions shows that NO product is relatively unreactive. Its initial rate of production can be used to yield directly the unimolecular rate constant, which in the fall‐off region, can be represented by the second‐order rate coefficient in the Arrhenius form:

A RRKM model calculation, assuming a loose CH3ONO≠ complex with two degrees of free internal rotation, gives good agreement with the experimental rate constants.
A pulse radiolysis study of I and (SCN) in aqueous solutions over the temperature range 15–90°C
Authors: Elliot Allen John , Sopchyshyn Frederick Charles
Published: January 2005

The extinction coefficients and the decay kinetics of I and (SCN) have been characterized over the 15–90°C‐temperature range. The extinction coefficients of I at 385 and 725 nm were determined to be 10,000 and 2560M−1 cm−1, respectively, based on the extinction coefficient of (SCN) at 475 nm being equal to 7600M−1 cm−1. At these three wavelengths, all extinction coefficients were constant over the temperature range studied. The rate of decay of both I and (SCN) was found to be a function of I− and SCN− concentration, respectively, as well as temperature.
Mechanism of propane oxidation–mathematical modeling
Authors: Levitsky A. A. , Polyak S. S. , Shtern V. Ya.
Published: January 2005

Mathematical modeling was used for the kinetics of gas‐phase propane oxidation at 586, 613, and 658 K and pressures 172 and 250 torr. The reaction mechanism involving branching by decay of the peracetyl peroxy radical, and oxygen‐containing products formed on decay of the RO4 radical is discussed. Fair agreement between calculated and experimental results on the kinetics and accumulation rates of reaction products was obtained.
Conversion effect on the reaction CF3 + HCN. Analysis of I2 and I participation with CF3I as radical source
Authors: Lane S. I. , Oexler E. V. , Staricco E. H.
Published: January 2005

The gas‐phase reaction of CF3 with HCN has been examined over a wide conversion range using CF3I as a thermal and photolytic source of radicals. Quantitative and qualitative results show a significant increase of the specific rate constant for the hydrogen abstraction reaction relative to CF3 recombination when reaction is carried out under ultraviolet irradiation. This “extra” formation of the reaction product, CF3H, has been assigned to the participation of iodine in this system through the formation of a (I‐HCN) intermediate. Arrhenius parameters obtained for the addition mechanism of I to HCN do not seem to conform to a single reaction step, on the contrary, they correspond to a more complex reaction scheme.
The kinetics and mechanism of the shock induced gas phase decomposition of ethylsilane
Authors: Rickborn S. F. , Ring M. A. , O'Neal H. E.
Published: January 2005

The decomposition kinetics of ethylsilane under shock tube conditions (PT ca. 3100 torr, T ≃ 1080–1245 K), both in the absence and presence of silylene trapping agents (butadiene and acetylene) are reported. Arrhenius parameters under maximum butadiene inhibition are: log k(C2H5SiH3) = 15.14‐64,769 ± 1433 cal/2.303 RT; log k(C2H5SiD3) = 15.29‐66,206 ± 1414/2.303 RT. The uninhibited reaction is subject to silylene induced decomposition (63% lowest T ‐‐ 24% highest T). Major reaction products are ethylene and hydrogen, consistent with two dominant primary dissociation reactions: C2H5SiD3 → C2H5SiD + D2, ϕ ≃ 0.66; C2H5SiD3 → CH3CH = SiD2 + HD, ϕ ≃ 0.30. Minor products suggest several other less important primary processes: alkane elimination, ϕ ≃0.02, and free‐radical production via simple bond fission, ϕ ≃0.02. An upper limit for the activation energy of the decomposition, C2H5SiH → C2H4 + SiH2, of E < 30 ± 4 kcal is established, and speculations on the mechanism of this decomposition (concerted or stepwise) with conclusions in favor of the stepwise path are made. Computer modeling studies for the reaction both in the absence and presence of butadiene are shown to be in good agreement with the experimental observations.
Products and mechanism for the OH radical initiated oxidation of acrylonitrile, methacrylonitrile, and allylcyanide in the presence of NO
Authors: Hashimoto Satoshi , Bandow Hiroshi , Akimoto Hajime , Weng Jian‐Hua , Tang Xiao‐Yan
Published: January 2005

The photooxidation of acrylonitrile, methacylonitrile, and allylcyanide in the presence of NO was studied in parts per million concentration using the long‐path Fourier transform IR spectroscopic method. The stoichiometry of the OH radical initiated oxidation of methacrylonitrile was established as \documentclass{article}\pagestyle{empty}\begin{document}$ \left( {{\rm OH}} \right) + {\rm CH}_{\rm 2} = {\rm C}\left( {{\rm CH}_{\rm 3} } \right){\rm CN + 2NO + 2O}_{\rm 2} \mathop {\hbox to 20pt{\rightarrowfill}}\limits^{1.0} {\rm HCHO + CH}_{\rm 3} {\rm COCN + 2NO}_{{\rm 2}} + \left( {{\rm OH}} \right) $\end{document}. The yield of HCHO for acrylonitrile and allylcyanide was found to be ca. 100 and 80%, and the stoichiometric reactions were assessed to proceed, \documentclass{article}\pagestyle{empty}\begin{document}$ \left( {{\rm OH}} \right) + {\rm CH}_{\rm 2} = {\rm CHCN + 2NO + 2O}_{\rm 2} \mathop {\hbox to 20pt{\rightarrowfill}}\limits^{1.0} {\rm HCHO + HCOCN + 2NO}_{\rm 2} + \left( {{\rm OH}} \right) $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ \left( {{\rm OH}} \right) + {\rm CH}_{\rm 2} = {\rm CHCH}_{\rm 2} {\rm CN + 2NO + 2O}_{\rm 2} \mathop {\hbox to 20pt{\rightarrowfill}}\limits^{0.8} {\rm HCHO + HCOCH}{\rm 2} {\rm CN + 2NO}_{\rm 2} + \left( {{\rm OH}} \right) $\end{document}, respectively. These results revealed that the reaction mechanism for these unsaturated organic cyanides are analogous to that of olefins.
High‐pressure range of the recombination O + O2 → O3
Authors: De Cobos A. E. Croce , Troe J.
Published: January 2005

The recombination reaction O + O2 → O3 was studied by laser flash photolysis of pure O2 in the pressure range 3–20 atm, and of N2OO2 mixtures in the bath gases Ar, N2, (CO2, and SF6) in the pressure range 3–200 atm. Fall‐off curves of the reaction have been derived. Low‐pressure rate coefficients were found to agree well with literature data. A high‐pressure rate coefficient of k∞ = (2.8 ± 1.0) × 10−12 cm3 molecule−1 s−1 was obtained by extrapolation.
On the temperature dependence of the activation enthalpy for sucrose hydrolysis
Authors: Ward J. Richard
Published: January 2005

Recent interest in the measurement and the interpretation of heat capacities of activation has led to more rigorous methods to detect temperature‐varient activation parameters. One such method devised by Blandamer and co‐workers was applied to the sucrose hydrolysis data of Moelwyn‐Hughes and Leininger and Kilpatrick. Both sets of investigators claimed that the energy of activation for sucrose inversion decreased with increasing temperature, while Heidt and Purvis and more recently, Kuhler's group contend that the energy of activation is constant. It was found that neither the data of Moelwyn‐Hughes nor of Leininger and Kilpatrick warrant the inclusion of a temperature‐dependent activation enthalpy.
Kinetics study of the reaction HO + HNO3
Authors: Connell Peter S. , Howard Carleton J.
Published: January 2005

The reaction
equation image
has been studied using a discharge‐flow tube with resonant fluorescence detection of HO. Measurements of k1 have been made at temperatures between 237 and 404 K. Our results and earlier work suggest that the rate constant has a minimum at T ≃ 500 K. Below room temperature our results are given by the expression k = (2.0 ± 0.4) × 10−14 exp[(430 ± 60)/T] cm3 molecule−1 s−1, where the error limits include an estimate of the measurement accuracy. No dependence of k1 on pressure at 300 K is observed in studies between 1‐ and 10‐torr helium. An upper limit of kb < 1% k1 at 300 K is given.
Decomposition of chemically activated dimethylcyclopropane molecules vibrationally excited to various extent
Authors: Bérces T. , Szilágyi I. , Zalotai L. , Márta F.
Published: January 2005

The photolyses of ketene (at 313 and 280 nm) and diazirine at 313 nm in the presence of cis‐butene‐2 were studied. Vibrational relaxation of chemically activated dimethylcyclopropane was shown to occur as a multistep process, and 17 ± 4 kJ mol−1 was obtained for the average energy transferred per collision with butene‐2 collider. Activated cis‐dimethylcyclopropane is formed in the reaction of singlet methylene and cis‐butene‐2 with broad energy distribution which originates from the energy partitioning in the photolytic act. About 30% of the energy released in the photolysis of the methylene source is carried by singlet methylene as vibrational energy at the time of reaction, and this fraction was found to be practically independent of the radical source.
Pyrolysis of 1‐chloro‐1,1‐difluoroethane in the absence and in the presence of CCl4 and mixtures of CCl4 + HCl
Authors: Huybrechts G. , Hubin Y.
Published: January 2005

The thermal dehydrochlorination CF2ClCH3 → CF2  CH2 + HCl has been studied in a static system between 637 and 758 K. It is a homogeneous, molecular first‐order reaction and its rate constant is given by

This reaction has also been studied in the presence of CCl4 and mixtures of CCl4 and HCl between 585 and 662 K. It is then accelerated and the initial rate increase is given by

with log10 (k′, L½ /mol½ · s) = −(41,650 ± 180)/4.576T + (10.84 ± 0.06) and log10 k″ = (7900 ± 180)/4.576T − (0.59 ± 0.06). A radical chain mechanism is shown to be consistent with these latter results.
The kinetic and mechanism of the gas phase pyrolysis of 1,1,1,2‐tetrachloropropane
Authors: Domínguez Rosa M. , Chuchani Gabriel
Published: January 2005

The gas phase pyrolysis of 1,1,1,2‐tetrachloropropane was studied in a static system and seasoned vessel over the temperature range of 393.0–452.8°C and pressure range of 27.5–118.5 torr. The reaction is homogeneous, unimolecular, follows a first‐order rate law, and is not affected by the presence of the free radical inhibitor, toluene, or propene. The main dehydrochlorination products are 1,1,1‐trichloro‐2‐propene and 1,1,2‐trichloro‐1‐propene. The temperature dependence of the rate coefficient is given by the Arrhenius equation

The Arrhenius parameters of this reaction are apparently low. Consequently, in estimating the transition state of A = 1013.5, the following expression is obtained

The partial rates and kinetic parameters for the parallel elimination products have been estimated and reported. The trichloromethyl substituent has been found to affect this elimination process through its electron withdrawing effect.
Pyrolysis of 2‐phenylethylamines heats of formation of aminomethyl radicals R2NCH2 · (R = H, CH3)
Authors: Grela M. A. , Colussi A. J.
Published: January 2005

A kinetic study of the very low‐pressure pyrolysis of ethylbenzene (I), 2‐phenylethylamine (II), and N,N‐dimethyl 2‐phenylethylamine (III)
equation image
above 900 K yields the heats of formation of aminomethyl (A) and N,N‐dimethylaminomethyl (B) radicals: ΔHƒ, 300 K(A) = 30.3 and ΔHƒ, 300 K(B) = 27.5 kcal/mol. The difference of stabilization energies Es, (relative to methyl radicals): Δ = Es(B) − Es(A) = (2 ± 1) kcal/mol, conforms to similar effects in methyl substituted alkyl and amino free radicals.
On the interaction of hydroperoxide and inhibitor molecules
Authors: Héberger K.
Published: January 2005

Decomposition of 1‐phenylethyl‐hydroperoxide has been studied in the presence of 2,6‐di‐tert‐butyl‐4‐methyl‐phenol inhibitor in ethylbenzene and chlorobenzene both in oxygen and nitrogen. The oxygen consumption and the inhibitor concentrations were measured against the initial inhibitor concentrations. Two methods were applied for the determination of the rate coefficients of the reaction:

Its value is about 3 × 10−4L × mol−1 × S−1, at 120°C. However, large experimental errors we deal with, the existence of a reaction yielding radicals, presumably an interaction between hydroperoxide and inhibitor molecules, can be established emphasizing the importance of measurements carried out with various initial concentrations of the inhibitor.
Disproportionation reactions between alkyl and fluoroalkyl radicals. III. A reassessment of Δ values for CFyH(3−y) radicals (y = 1,2,3) with C2H5 radicals
Authors: Pritchard G. O. , Johnson K. A. , Nilsson W. B.
Published: January 2005

New determinations of the disproportionation and combination ratios between CF2H and C2H5 radicals yield (the hydrogen acceptor radical is given first) Δ(CF2H, C2H5) = 0.068 ± 0.008, and Δ(C2H5, CF2H) = 0.37 ± 0.01. A reevaluation of the existing data on CFH2 and CF3 radicals leads to the following recommended values, Δ(CFH2, C2H5) = 0.038 ± 0.006, and Δ(CF3, C2H5) = 0.11 = ± 0.02.
Reactions of alkoxy radicals with O2. I. C2H5O radicals
Authors: Zabarnick Steven , Heicklen Julian
Published: January 2005

C2H5ONO was photolyzed with 366 nm radiation at −48, −22, −2.5, 23, 55, 88, and 120°C in a static system in the presence of NO, O2, and N2. The quantum yield of CH3CHO, Φ{CH3CHO}, was measured as a function of reaction conditions. The primary photochemical act is
equation image
and it proceeds with a quantum yield ϕ1a = 0.29 ± 0.03 independent of temperature. The C2H5O radicals can react with NO by two routes
equation image
The C2H5O radical can also react with O2 via
equation image
Values of k6/k2 were determined at each temperature. They fit the Arrhenius expression: Log(k6/k2) = −2.17 ± 0.14 − (924 ± 94)/2.303 T. For k2 ≃ 4.4 × 10−11 cm3/s, k6 becomes (3.0 ± 1.0) × 10−13 exp{−(924 ± 94)/T} cm3/s. The reaction scheme also provides k8a/k8 = 0.43 ± 0.13, where
equation image
Primary photochemical processes in the photolysis of alkyl nitrites at 366 NM and 23°c in the presence of 15NO
Authors: Morabito Paul , Heicklen Julian
Published: January 2005

The alkyl nitrites, C2H5ONO, n‐C3H7ONO, n‐C4H9ONO, and i‐C4H9ONO were photolyzed at 23°C in the presence of 15NO at 366‐nm incident radiation. The quantum yields of the corresponding isotopically‐enriched alkyl nitrites were measured by mass spectrometry. The results indicated that only part of the absorption leads to photodecomposition. The remainder forms an electronically excited state which isotopically exchanges with 15NO. The indicated reactions of the electronically excited state RONO*, are
equation image
where k3/k2 = 0.50 ± 0.10, 0.62 ± 0.20, 0.42 ± 0.06, and 0.24 ± 0.03 torr, and that k2a/k2 = 1.0, 1.0, 0.64 ± 0.04, and 0.56 ± 0.03, respectively, for C2H5ONO, n‐C3H7ONO, n‐C4H9ONO, and i‐C4H9ONO.
Autocatalysis and bistability in the reaction between nitric acid and thiocyanate
Authors: Bazsa Gyöurgy , Epstein Irving R.
Published: January 2005

The reaction between nitric acid and thiocyanate has been studied both in batch and flow configurations. The batch reaction is autocatalytic with an induction period which is decreased by the addition of HNO2. At the nitric acid concentrations employed (1–10 M), a red NOSCNH+ intermediate is formed. The reaction in a flow reactor exhibits bistability. A model involving competitive reactions of SCN− and NOSCNH+ with NO2 is suggested, and computer simulations with this model give good agreement with both the batch and flow experiments.
Direct comparison of methods for extracting the rate from first order data with background
Authors: McKinnon G. H. , Backhouse C. J. , Kalantar A. H.
Published: January 2005

Many methods involving a lag or retardation can linearize A exp(−kt) + Z data, allowing k to be obtained from the slope. A classification scheme is found in which the efficiencies are related to the classes of methods. The methods yielding k with the smallest standard deviations (σk) are compared quantitatively. The resulting error factors for k and the lags are tabulated for each of the four methods compared, for use by the experimenter. This is done for various ranges, backgrounds, and kinds of random noise. Effects on k and σk due to correlation, incorrect weighting, choice of lag, and the distribution of the plotted data are detailed. Effects at high noise levels are discussed for the (usually) best direct method, due to Guggenheim. These include the onset and extent of bias in k and failure of the method to yield any k.
Extent of H‐atom abstraction from the reaction of the OH radical with 1‐butene under atmospheric conditions
Authors: Atkinson Roger , Tuazon Ernesto C. , Carter William P. L.
Published: January 2005

Products of the reaction of OH radicals with 1‐butene have been investigated in the presence of NO in one atmosphere of air at room temperature using gas chromatography and in situ long pathlength Fourier transform infrared absorption spectroscopy. The major product observed was propionaldehyde, with a formation yield (after allowing for its subsequent loss processes) of 0.94 ± 0.12. Minor yields of organic nitrates (RONO2) and of peroxypropionyl nitrate, a secondary product arising from propionaldehyde, were also observed. However, none of the products expected from the reactions subsequent to H‐atom abstraction from 1‐butene by OH radicals were observed, allowing an upper limit of 10% for this process to be derived. These data are compared with the available literature results and the implications are discussed.
Kinetics of reversible recombination of aromatic C‐centered radicals
Authors: Margulis L. A. , Khudyakov I. V. , Kuzmin V. A. , Prokof'ev A. I. , Yasmenko A. I. , Smets G.
Published: January 2005

The kinetics of the reversible recombination of the 2‐phenyl‐ (I), 2‐p‐methoxyphenyl‐(II), and 2‐p‐nitrophenyl‐3‐oxo‐2,3‐dihydrobenzothiophene‐2‐yl (III) radicals
equation image
have been investigated. Recombination rate constants of R(I–III) have been determined in different solvents (2k1 ∼ 109 M−1 s−1). The rate of reaction (I) with R(I–III) decreases with increasing solvent viscosity η. In the toluene‐vaseline oil mixture (2 ≲ η ≲ 120 cP) the recombination of R(I–III) is molecular mobility limited. The thermodynamic parameters of reaction (I) have been determined: ΔH0 = 20–30 kcal/mol. Activation volumes ΔV for recombination of R(II) have been measured. In n‐propanol ΔV is equal to the viscous flow activation volume of the solvent ΔV. In toluene and chloroform ΔV < ΔV. For the last two solvents the activation volumes of the cage reaction have been estimated ΔV = −(2–3) cm3/mol. Visible‐range absorption spectra and ESR spectra have been recorded for R(I–III). The role of cage effect in the reactivity anisotropy averaging of R(I–III) is discussed. The potential of the high‐pressure tests for deriving information about the elementary act of a fast bimolecular reaction is considered.
Pyrolysis of 2‐methylbut‐1‐ene‐3‐yne between 375 and 450°c
Authors: Chanmugathas C. , Heicklen Julian
Published: January 2005

The pyrolysis of 2‐methylbut‐1‐ene‐3‐yne (C5H6) has been studied from 375 to 450°C in a quartz reaction vessel in the absence and presence of O2 or NO. From 375 to 425°C, the rates of disappearance of reactant and of formation of dimers are second order in C5H6. The major product is polymer, with the dimers accounting for about 3% of the C5H6 consumed. In addition, toluene and p‐xylene are produced, their production coming, at least in part, from decomposition of the C5H6 dimers (C10H12). Also, trace amounts of CH4, C2H4, C2H6, are formed. The rate coefficients for C5H6 removal and C10H12 formation in the absence of O2 or NO are

where the uncertainties are one standard deviation. The reaction mechanism for dimer formation is analogous to that in vinyl acetylene (C4H4) pyrolysis (5), except that in the C4H4 system cyclooctatetraene is seen as an unstable product that isomerizes to styrene, whereas in the C5H6 system, the dimethylcyclooctatetraene apparently is too unstable to be detected. The dimers detected were 2,6‐dimethylstyrene (P4), p‐isopropenyltoluene (P5), and two other unidentified dimers (P3) with nearly identical gas chromatographic retention times. From the effect of the radical scavengers and by comparison of the C4H4 and C5H6 systems, the following mechanistic characteristics were determined: (1) The direct formation of styrene in the C4H4 system comes from a head‐to‐head modified Diels‐Alder six‐member cycloaddition that proceeds through a diradical intermediate. (2) There is no positive evidence for a direct head‐to‐tail modified Diels‐Alder six‐member cycloaddition. However, if it does occur, it does not involve diradicals but must be concerted. (3) Cyclooctatetraene is formed in concerted, non‐free‐radical mechanisms that may proceed both by head‐to‐head and head‐to‐tail eight‐member cycloadditions. For the C5H6 system, the head‐to‐head adduct isomerizes to P3, whereas the head‐to‐tail adduct isomerizes to P3, P4, and/or P5. and/or P5. Kinetic data suggest that P3 is not produced from the cyclooctatetraene intermediate, in which case, head‐to‐head addition would not occur. It appears that the head‐to‐head additions are free radical in nature and proceed mainly through a six‐membered ring intermediate, while head‐to‐tail additions are a concerted molecular process and proceed mainly through an eight‐membered ring intermediate.
On the mechanism of thermal oxidation of methane
Authors: Vardanyan I. A. , Nalbandyan A. B.
Published: January 2005

Using the method of freezing radicals in conjunction with ESR spectroscopic measurements, the kinetics of the thermal oxidation of methane has been studied under atmospheric pressure depending on the temperature, composition of the mixture, and nature of the surface of the reaction vessel. It has been shown that in a reactor treated with boric acid, the intermediates methylhydroperoxide and hydrogen peroxide are responsible for chain branching. It has been established that the leading active centers of the reaction are the HO2 radicals, while chain branching occurs as a result of the decomposition of peroxy compounds—methylhydroperoxide and hydrogen peroxide. In reactors treated with potassium bromide, the concentrations of radicals and peroxy compounds were found to be lower than the sensitivity of the method of measurement. Computations were performed for the scheme of methane oxidation at 738 K for a reactor treated with boric acid. Satisfactory agreement was found between the experimental and computed kinetic curves of accumulation of main intermediates CH2O, H2O2, CH3OOH. The influence of their addition on the kinetics of the reaction has been considered. It has been shown that the addition of formaldehyde does not lead to chain branching, however; it contributes to the formation of those peroxy compounds that bring about chain branching. Mathematical modeling confirmed conclusions made on the basis of experimental data concerning the nature of the leading active centers and the products that are responsible for the degenerate chain branching.
A continuous stirred tank reactor investigation of the gas‐phase reaction of hydroxyl radicals and toluene
Authors: Gery Michael W. , Fox Donald L. , Jeffries Harvey E. , Stockburger Leonard , Weathers Walter S.
Published: January 2005

A continuous stirred tank reactor (CSTR) was used to study the gas‐phase reaction between HO⋅ and toluene. HO⋅ was generated by the in situ photolysis of nitrous acid. Flow reactor operation at steady‐state conditions with a residence time of 20 min allowed investigation of primary and very rapid secondary reactions. CSTR and batch reactor experiments were also performed with selected products. Both gas‐phase and aerosol products were identified by chromatography and mass spectroscopy, with total product yields between 55 and 75% of reacted carbon. Toluene reaction products included cresols, nitrocresols, nitrotoluenes, 3,5‐dinitrotouluene, benzaldehyde, benzyl nitrate, nitrophenols, methyl‐p‐benzoquinone, glyoxal, methylglyoxal, formaldehyde, methyl nitrate, PAN, and CO. The fraction of HO⋅ methyl hydrogen abstraction was calculated to be 0.13 ± 0.04. The ratio of reaction rate constants for nitrotoluene versus cresol formation from the HO⋅‐adduct was calculated to be about 3.3 × 104. Also, the ratio of cresol formation versus O2 addition to the HO⋅‐adduct was estimated to be ≥0.5 for atmospheric conditions. Comparisons of these measurements with previous values and the implications with respect to photochemical kinetics modeling of the atmosphere are discussed.
Mechanism and kinetics of the silane decomposition in the presence of acetylene and in the presence of olefins
Authors: Erwin J. W. , Ring M. A. , O'Neal H. E.
Published: January 2005

Kinetic data and product studies are reported for the silane pyrolysis in the presence of olefins and acetylene. The kinetics of silane loss in the presence of acetylene was found to be identical to the initial gas phase silane decomposition step (SiH4 + M → SiH2 + H2 + M) when corrected for pressure fall‐off effects. This result and the absence of methane or ethane from the pyrolysis of SiH4 in the presence of 1‐butene or 1‐pentene demonstrate that silyl radicals and H atoms are not involved in silane‐olefin or silane‐acetylene reactions. Qualitative aspects and kinetic data from the SiH4 pyrolysis in the presence of propylene are in accord with propylsilane formation via propylsilylene formed by silylene addition to propylene.
Comments on the linear relation between reaction rate and affinity
Authors: Boudart Michel , Löffler Daniel G. , Gottifredi Juan Carlos
Published: January 2005

In the case of catalytic dehydrogenation of cyclohexane, the linear relation between reaction rate and affinity holds at an appreciable distance away from equilibrium on both sides. In fact, in order to explain this observation, it is necessary to invoke a high value of three for the stoichiometric number of the rate determining step. This in turn can be explained by a reasonable mechanism for the reaction.
Kinetics and mechanism of electron transfer via bridge metal‐ion
Authors: Maletin Y. A. , Strizhakova N. G.
Published: January 2005

The kinetics and mechanism of electron transfer between stable verdazyl radicals via bridge Mn(II), Co(II), Ni(II), Cu(I), and Zn ions have been studied in the range 280–330 K using the stopped‐flow technique. It was found that the kinetic features of the reactions could be described in terms of the Marcus theory. The reorganization energy of the inner coordination sphere (ICS) of intermediate complexes was estimated from the reported data on the energy of release of various ligands from the ICS of similar complexes. The rest of the kinetic parameters (solvent reorganization energy, transmission coefficients, enthalpy, and entropy of activation) were determined from Marcus equations and from plots of rate constant versus temperature, “standard” free energy, and polarity of the medium. It was also found that the reactions under consideration are nonadiabatic and the transmission coefficient value depends on the mean lifetimes of ligands in the ICS.
Kinetics of the gas phase reaction of OH radicals with pyrrole and thiophene
Authors: Wallington Timothy J.
Published: January 2005

Absolute rate constants for the gas phase reaction of OH radicals with pyrrole (k1) and thiophene (k2) have been measured over the temperature ranges 298–440 and 274–382 K, respectively, using the flash photolysis‐resonance fluorescence technique. The rate constants obtained were independent of the total pressure of argon diluent over the range 25–100 torr andwere fit by the Arrhenius expressions

and

with rate constants at 298 ± 2 K of k1 = (1.03 ± 0.06) × 10−10 cm3 molecule−1 s−1 and k2 = (8.9 ± 0.7) × 10−12 cm3 molecule−1 s−1. [These errors represent two standard deviations (systematic errors could constitute an additional ca. 10% uncertainty)]. These results are discussed with respect to the previous literature data and the atmospheric lifetimes of pyrrole and thiophene.
Temperature dependence of the quasiclassical reactivity for vibrationally excited hydrogen molecules colliding with hydrogen atoms
Authors: Laganà A.
Published: January 2005

A discussion of reactants vibrational energy and temperature dependence of reactive rate constants for the hydrogen atom hydrogen molecule reaction is presented for a matrix of values calculated at 0 < v <10 and temperatures in the range from 300 K to 4000 K. A parametrization ofthe results is attempted. A comparison with rate constant values obtained from an approximate quantum treatment is also reported.
The Heterogeneous Reaction of Ozone on Carbonaceous Surfaces
Authors: Stephens Sherry , Rossi Michel J. , Golden David M.
Published: January 2005

Ozone, O3, reacts with a carbon sample at room temperature. Clean carbon samples show a half to one and a half order of magnitude increased initial rate constant (k0) for O3 loss relative to repetitively exposed carbon samples. The ozone loss rate and therefore the rate constant reaches steady state (kss) on the time scale of tens of minutes, upon exposure to a characteristic dose of 8 × 1017 molecules for a 30‐mg carbon sample independent of the flow rate. This characteristic dose closely corresponds to a monolayer of adsorbed ozone molecules on the carbon sample. Both k0 and kss decrease with increasing flow rate of O3 into the reactor, and the loss rate is found to depend on [O3]. When the loss rate is plotted against the steady state concentration of O3, a saturation plot results which is proportional to the surface coverage, θ, at a given [O3].This interpretation rests upon a Langmuir type kinetics model with an assumed first‐order dependence of the loss rate constant. The “sticking coefficients” track the rate constants and are on the order of 10−3 to 10−5 depending on the carbon sample, dose, and flow rate. Furthermore, ko depends on the length of the dark period (absence of O3 exposure) and is larger the longer time the sample has had to recuperate from previous O3 exposures up to a period of 150 s. This surface relaxation is thought of as a time‐dependent change in surface coverage taking place in the dark period and is therefore an indication of a slow surface diffusion/reaction that can be separated from the adsorption‐desorption kinetics. The mass balance shows that for every ozone molecule that is lost on the surface, an oxygen molecule is found. This adsorbed odd oxygen is then responsible for product formation, which comprises the volatile components CO and CO2 to an extent of 20 to 40% of the odd oxygen deposited on the surface. The difference is thought to be in a preoxidized state on the carbon sample, which evolves CO and CO2 upon heat treatment.
Kinetic evidence for the occurrence of trianionic tetrahedral intermediate in the hydroxide ion‐catalyzed cleavage of 1, 2‐benzisothiazolin‐3‐one‐1, 1‐dioxide (saccharin)
Authors: Khan M. Niyaz , O M. S. O.
Published: January 2005

The kinetics of hydrolytic cleavage of saccharin has been studied at 60°C within the [ŌH] range of 0.1 to 3.0 M. The observed pseudo first‐order rate constants, kobs, follow an empirical relationship: kobs = B[ŌH] + [C[ŌH]]2. The B and C terms are attributed to the formation of dianionic and trianionic tetrahedral intermediates on the reaction path. It is concluded that the ionized form of saccharin is the major reacting species under the present experimental conditions. The positive ionic strength effect and the negative effect of 1,4‐dioxan on the rate of hydrolysis favor the proposed reaction mechanism. The analysis of the observed activation parameters indicates that the increase in the contribution of C term to kobs causes the slight increase in both ΔH* and ΔS*. A significantly large negative value of ΔS* favors the proposed mechanism.
Transient kinetic studies involving exciplex formation. Methods of analysis
Authors: Richer Jacques , Lessard Ginette , Belletěte Michel , Durocher Gilles
Published: January 2005

In this paper, rate parameters are extracted from fluorescene decay data in the framework of Feedback‐Type Kinetics (k8 < k4). The exciplex dissociation (k4) and fluorescene decay rate constants (k8) have been obtained for the five following systems:
equation image
For this task we have added to the straight line method of Ware which is valid in certain cases only at high perturber concentrations, a new but similar Taylor series method applicable at low concentrations. Thereafter, a safer and more general method of kinetic analysis based on a quasi‐linear χ2 minimization procedure has been developed and applies to data in any range of concentration.
An FTIR spectroscopic study of the kinetics and mechanism for the NO2‐initiated oxidation of tetramethyl ethylene at 298 K
Authors: Niki H. , Maker P. D. , Savage C. M. , Breitenbach L. P. , Hurley M. D.
Published: January 2005

The kinetics and mechansim for the NO2‐initiated oxidation of tetramethyl ethylene (TME) have been studied using the FTIR spectroscopic method in mixtures containing NO2 and TME (0.1−1.0 Torr) and N2O2 (700 Torr) at 298 ± 2 K. While TME decayed according to ‐d[TME]/dt = kobs[NO2][TME], NO2 exhibited a complex kinetic behavior. Furthermore, values of kobs were dependent on [O2]. Among the products were (CH3)2CO and at least three NO2‐containing compounds. These results indicate the formation of a nitro‐alkylperoxy radical via reactions (1), (−1), and (2), and its subsequent reactions leading to the observed products.
equation image
The [O2]‐dependence of kobs yielded k1 = (1.07 ± 0.15) × 10−20 cm3 molecule−1 S−1 and k−1/k2 = (3.54 ± 0.61) × 1018 molecule cm−3.
Kinetics and mechanism of electron transfer from phenolate anion to hexacyanoferrate (III) in aqueous alkaline media
Authors: Panda Pradeepta K. , Panda Rama Krushna , Murti P. S. Radhakrishna
Published: January 2005

A kinetic reinvestigation of the title redox system in aqueous alkaline media at 35°C and an ionic strength of 0.5 mol dm−3shows that the reaction follows a pseudosecond‐order Fe(CN)disappearance. While varying [phenol]0and [OH−] exhibit a linear influence on the pseudo‐second‐order rate constant, varying[Fe(CN)]0and [Fe(CN)]0, initially taken, have a complicated inhibitory effect on the same. The major phenoloxidation products isolated under a chosen condition are 2,2′‐ and 4,4′‐ dihydroxydiphenyl. Results are interpreted in terms of a probable mechanism which envisages a reversible formation, by the first one‐electron transfer, of a reactive phenoxy radical (PhO˙) which on the second one‐electron transfer forms a less reactive ion‐pair intermediate (stabilized by the Fe(CN)produced) to decompose rate‐determiningly to phenoxonium cation (PhO+) and Fe(CN), the product‐formation steps being very rapid and kinetically indistinguishable.
Investigation of the gas phase reaction of dinitrogen pentoxide with water vapor
Authors: Sverdrup George M. , Spicer Chester W. , Ward Gerald F.
Published: January 2005

The gas phase reaction of N2O5 with water vapor was investigated in a 17.3‐m3 Teflon lined chamber. Temporal concentration profiles for ozone, total nitrogen oxides, and nitrogen dioxide were measured. Concentration profiles for N2O5 and HNO3 were calculated from a combination of measurements of nitrogenous species. A kinetic mechanism with an adjustable value for the rate constant of N2O5 + H2O was used to model the experiments. From this analysis an upper limit value of k ⩽ 4 × 10−7 ppm−1 min−1 for the gas phase reaction N2O5 + H2O → 2HNO3 was derived.
Direct and sensitized photolysis of bicyclo[4.2.0]octa‐2,4‐diene in the gas phase
Authors: Greathead John M. , Orchard S. Walter
Published: January 2005

The direct photolysis of bicyclo[4.2.0]octa‐2,4‐diene in the gas phase at 280–300 nm produces mainly 1,3,5‐cyclooctatriene and benzene plus ethylene. The yield of the former product is enhanced by added gases, and it is proposed that it is formed in a vibrationally excited state which can revert to bicyclooctadiene unless the excess energy is removed in collisions. Computer modelling of the direct photolysis yielded quantitative agreement with the experimental results, but only when large, arbitrary adjustments were made to the calculated rate constants for the interconversion of cyclooctratriene and bicyclooctadiene. The Hg(63P1) sensitized reaction of bicyclooctadiene produces mainly benzene plus ethylene, a process which is also enhanced by added gases.
Cross‐reaction and cross‐combination ratios
Authors: Arthur Neville L. , Christie John R.
Published: January 2005

A simple collision theory model for reaction between two different radicals shows that the cross‐reaction ratio, ϕ*, is 2 only if the masses and collision diameters of the radicals are identical; for all other combinations of mass and size, ϕ* is greater than 2. The value of ϕ* is shown to depend simply on the ratios of the masses and diameters of the two radicals: which of the two is the heavier or larger is unimportant.

Calculated and experimental values of ϕ* are compared for several systems involving small alkyl and fluoroalkyl radicals, and the relationship between ϕ* and ϕ, the cross‐combination ratio, is discussed.
Decomposition of the t‐butoxy radical — I. Studies over the temperature range 402–443 K
Authors: Batt L. , Robinson G. N.
Published: January 2005

By allowing the t‐butoxy radical to decompose in the presence of nitric oxide, it has been possible to determine rate constants for decomposition by the measurements of the relative rates (2) and (3)
equation image
Process (3) is clearly pressure dependent. The value of k3(∞) has been determined in the presence of several inert gases (CF4, SF6, N2, and Ar) and a value of k3 interpolated for atmospheric conditions. The results may be compared with those for other relevant alkoxy radicals at room temperature. Extrapolated values for k3 in the presence of CF4 lead to the result
Artificial‐intelligence‐based interpretation of feature sensitivities of the Belousov‐Zhabotinsky reaction
Authors: Györgyi L. , Deutsch T. , Kőrös E.
Published: January 2005

A new approach is presented for analyzing kinetic models of relaxation‐type oscillatory systems on the basis of numerical data. Feature sensitivities of the length of the two kinetic states of the Belousov‐Zhabotinsky (BZ) reaction with respect to the rate constants of the model are explained by means of a logic‐based inference system. The main kinetic roles of the individual reaction steps on the relaxing components are revealed, and a consistent interpretation of the kinetic states is given by this process. Both the high and the low set of rate constants were studied. According to our analysis, the bromous acid‐hypobromous acid reaction is an important Br− producing step of the model, and in the case of the low set, the bromate‐bromous acid reaction is not the rate‐determining step of the bromous acid autocatalysis.
Kinetics of the gas‐phase thermal elimination of N‐alkyl‐pyrazoles
Authors: Perez Jorge Daniel , Phagouape Leonardo Miguel
Published: January 2005

The kinetic study of the gas‐phase thermal elimination reactions of N‐ethyl‐3,5 dimethyl‐pyrazole (I), N‐ethyl‐pyrazole (II), N‐sec‐butyl‐pyrazole (III), and N‐tert‐butyl‐pyrazole (IV) using a flow system is reported. After obtaining activation parameters for I we carried out competitive reactions with II, III and IV using I as internal standard to obtain their Ea. The values of Δ(ΔH) calculated for II, III and IV agree with the little differences in Ea experimentally found.