ALBERT

Notes: The decomposition of dimethyl peroxide (DMP) was studied in the presence and absence of added NO2 to determine rate constants k1 and k2 in the temperature range of 391-432°K: \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{rcl} {{\rm DMP}} & \stackrel{1}{\longrightarrow} & {2{\rm MeO}} \\ {{\rm MeO + DMP}} & \stackrel{2}{\longrightarrow} & {{\rm MeOH + CH}_{\rm 2} {\rm O} + {\rm MeO}} \\ \end{array} $$\end{document} The results reconcile the studies by Takezaki and Takeuchi, Hanst and Calvert, and Batt and McCulloch, giving log k1(sec-1) = (15.7 ± 0.5) - (37.1 ± 0.9)/2.3 RT and k2 ≈ 5 × 104M-1· sec-1. The disproportionation/recombination ratio k7b/k7a = 0.30 ± 0.05 was also determined: \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{rcl} {{\rm MeO} + {\rm NO}_2 (+ {\rm M})} \stackrel{7a}{\longrightarrow} & {{\rm MeONO}_{\rm 2} (+ {\rm M})} \\ {{\rm MeO} + {\rm NO}_2} \stackrel{7b}{\longrightarrow} & {{\rm CH}_{\rm 2} {\rm O} + {\rm HONO}} \\ \end{array} $$\end{document}When O2 was added to DMP mixtures containing NO2, relative rate constants k12/k7a were obtained over the temperature range of 396-442°K: \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{rcl} {{\rm CH}_{\rm 3} {\rm O} + {\rm O}_2} \stackrel{12}{\longrightarrow} & {{\rm CH}_2 {\rm O} + {\rm HO}_{\rm 2}} \\ \end{array} $$\end{document} A review of literature data produced k7a = 109.8±0.5M-1·sec-1, giving log k12(M-1·sec-1) = (8.5 ± 1.5) - (4.0 ± 2.8)/2.3 RT, where most of the uncertainty is due to the limited temperature range of the experiments.

Notes: By means of the technique of laser-induced fluorescence, the room-temperature vibrational relaxation of DF(v = 1) has been studied in the presence of several polyatomic chaperones. The rate coefficients obtained [in units of (μ;sec·torr)-1] are CH4, 0.22; C2H6, 0.61; C4H10, 1.26; C2H2, 4.0 × 10-2; C2H2F2, 1.86 × 10-2; C2H4, 0.175; CH3F, 0.36; CF3H, 1.95 × 10-2; CF4, 1.0 × 10-3; CBrF3, 5.6 × 10-4; NF3, 5.1 × 10-4; SO2, 1.27 × 10-2; and BF3, 7.1 × 10-3. Results are also reported for vibrational relaxation rate coefficients for HF(v = 1) in the presence of the following chaperones: CH4, 2.6 × 10-2; C2H6, 5.9 × 10-2; C3H8, 8.4 × 10-2; and C4H10, 0.128. A comparison of DF and HF results indicates that for deactivation by CnHn+2, rate coefficients for DF are approximately an order of magnitude larger than for HF. The deactivation rate coefficient of DF(v = 1) by CH4 was found to decrease with increasing temperature between 300 and 740°K.

Notes: The reactions between alizarin yellow G and six different bases B (including OH-) and between tropaeolin 0 and eight different bases have been investigated at 25°C and an ionic strength of 0.5M, using the temperature-jump method. From the form of the log kB versus ΔpK curves it is concluded that for alizarin yellow G the observed relaxation time is due chiefly to a diffusion-controlled reaction between the base and that fraction which is present in the “open” non-hydrogen-bonded form, whereas for tropaeolin 0 the base attacks the hydrogen bridge.The dissociation constants for the internally bound hydrogen have been measured under the same conditions of temperature and ionic strength, using a spectrophotometric method.

Notes: The reaction of 1,3-cyclopentadiene (CPD) with ground-state atomic oxygen O(3P), produced by mercury photosensitized decomposition of nitrous oxide, was studied. The identified products were carbon monoxide and the following C4H6 isomers: 3-methylcyclopropene, 1,3-butadiene, 1,2-butadiene, and 1-butyne. The yield of carbon monoxide over oxygen atoms produced (φCO) was equal to the sum of the yields of C4H6 isomers in any experiment. φCO was 0.43 at the total pressure of 6.5 torr and 0.20 at 500 torr. We did not succeed in detecting any addition products such as C5H6O isomers.It was found that 3-methylcyclopropene was produced with excess energy and was partly isomerized to other C4H6 isomers, especially to 1-butyne. The excess energy was estimated to be about 50 kcal/mol.The rate coefficient of the reaction was obtained relative to those for the reactions of atomic oxygen with trans-2-butene and 1-butene. The ratios kCPD+O/ktrans-2-butene+O= 2.34 and kCPD+O/k1-butene+O = 11.3 were obtained.Probable reaction mechanisms and intermediates are suggested.

Notes: The kinetics of chlorine atom abstraction from the chloroethanes (EClH) 1,1,2-C2Cl3H3, 1,1-C2Cl2H4, and 1,2-C2Cl2H4 by radiolytically generated cyclohexyl radicals was studied in the liquid phase by a competitive method. The chlorine atom abstraction data were put on an absolute basis by comparing the rates of the metathetical reactions with the known rate of addition of cyclohexyl radicals to C2Cl4. The following Arrhenius parameters were obtained: TextE(EClH)-TemperatureA(ECLH)E(CCl4)log A(EClH)E(EClH)RangelogEClHA(C2Cl4)(kcal/mol)(1.mol·sec)(kcal/mol)(°C)CHCL2CH2Cl0.03 ± 0.083.87 ± 0.178.98 ± 0.1411.17 ± 0.27150 - 250CHCL2CH30.13 ± 0.134.63 ± 0.278.18 ± 0.1911.93 ± 0.37130 - 250CHCL2CH2Cl0.50 ± 0.177.57 ± 0.359.18 ± 0.2314.87 ± 0.45150 - 250The error limits are the standard deviations from least mean square Arrhenius plots.The α and ß activation effects on the kinetics of Cl atom abstraction from chloroalkanes are discussed. From the linear relation between the relative reactivities of cyclohexyl radicals toward the XCCl3 and XCHCl2 series, ECl(c-C6H11· + CHCl2CHCl2) = 10.2 ± 1 kcal/mol and ECl(c-C6H11· + CHCl22CCl3) = 9.7 ± 1 kcal is derived.

Notes: Reactions of OH(v = 1) with HBr, O, and CO have been studied at 295°K using a fast discharge flow apparatus: The reaction O + HBr → OH(v = 1) + Br was used as a source of OH(v = 1), and subsequent chemical reactions of the excited radical were followed using EPR spectroscopy. Rate constants for reactions (2b), (3b), and (6b) were measured as (4.5 ± 1.3) × 10-11, (10.5 ± 5.3) × 10-11, and 〈5 × 10-12 cm3/molec·sec, respectively. The rate constant for physical deactivation of OH(v = 1) by CO was determined as 〈4 × 10-13 cm3/molec·sec.

Notes: The reactions have been studied by a mass-balance method involving the photolysis of small amounts of biacetyl in the presence of a large excess of isobutane containing a small proportion of the unsaturated substrate. The following Arrhenius parameters have been derived: TextTemperatureElog ArangeReaction(kcal/mol)(1./mol·sec)(°K)ĊH3 + C2H4 → Ċ3H77.3 ± 1.08.32 ± 0.5350 - 500ĊH3 + C2H2 → Ċ3H57.7 ± 1.58.79 ± 0.8379 - 487ĊH3 + C6H6 → C7H97.6 ± 1.08.79 ± 0.5372 - 484The results for methyl addition to ethylene are based on previous determinations by other techniques as well as the present studies. The results for methyl addition to acetylene and benzene are derived solely from the present experiments and are calculated relative to a rate constant of log k2(l./mol·sec) = 7.42 - (7.1/θ) for the reference reaction (2), ·H3 + (CH3)3CH → CH4 + ·4H9.

Notes: The thermal decomposition of propene in the presence of D2 was studied in a single-pulse shock tube in the temperature range of 1200-1400°K. The main decomposition products were methane, ethylene, allene, and propyne. Furthermore, deuterated species were observed of each product and of propene, with characteristic compositions that were dependent on propene conversion. Geometrical isomers of monodeuterated propene, as the result of H-D exchange, were analyzed by microwave spectroscopy. From these observations, the reactivities of n- and isopropyl radicals at high temperatures were determined. The former was found to be an intermediate of methane and ethylene and the latter was found to be responsible for the formation of the deuterated propene as follows: The rate constant ratio kn/ki was estimated to be 0.5-0.8, which was more than ten times greater than that obtained at room temperature. It was also found that allene or propyne was produced from allyl radicals and that acetylene was produced from vinyl radicals. In addition, the rate constant of the hydrogen abstraction by the hydrogen atom from C3H6 was found to be six times greater than that by the hydrogen atom from D2.

Notes: The oxidation of cerous ions by bromate ions in sulfuric acid medium was followed spectrophotometrically under various experimental conditions. The results were compared to the calculated predictions on the basis of a mechanism suggested by R. M. Noyes and collaborators. The computations were done by solving the complete set of the kinetic differential equations. The results of the computations show that the proposed mechanism explains adequately most of our and previous experimental data. In particular, the mechanism predicts the main features of the reaction, namely, the induction and the fast and slow reaction periods which occur during the oxidation.

Notes: The thermal decomposition of NO2 and its atom-transfer reactions with SO2 and CO have been studied behind incident shock waves using photometric detection methods. From the decomposition study it is possible to obtain information on the rate of the reaction 2NO2 → antisymmetric-NO3 + NO. The results on the reaction, NO2 + SO2 → NO + SO3 extend the earlier work of Armitage and Cullis to about 2000°K. The reaction with CO [NO2 +] [CO NO + CO2] at shock temperatures is somewhat faster than predicted from available low-temperature data and provides a modification of the rate-constant expression that is applicable over a wide temperature range.

Notes: The kinetics of the reaction of cis-(NO)2 with solid oxygen to form iso-N2O4 have been studied between 13 and 29 K. The overall reaction is pseudo first order in cis-(NO)2, and solid oxygen serves both as a reactant and the matrix. The pseudo-first-order rate constants are calculated to be k(14N) = 4.25 × 10-2 exp(-103/RT), and k(15N) = 3.00 × 10-2 exp(-105/RT) sec-1, based on temperature measurements from a thermocouple junction which may be at most three degrees lower than the actual reacting film. Most significantly, however, 14k/15k = 1.55 at∼13 K. The condensed phase reaction has been compared to that observed in the gas phase, and the extremely small pre-exponential factors and large isotope effects have been discussed in terms of tunneling corrections and orientational constraints. It is suggested that the form of the crystal plays an integral role in the observed process.

Notes: The flash photolysis-vacuum ultraviolet kinetic absorption spectroscopy technique has been used to measure the absolute rate constant for the reaction of ground state S(3P) atoms withnitric oxide,\documentclass{article}\pagestyle{empty}\begin{document}${\rm S}\left({^{\rm 3} P} \right) + {\rm NO}\mathop {\longrightarrow}\limits^{\rm M} {\rm SNO}\left({{\rm M} = {\rm CO}_2} \right)$\end{document} as a function of nitric oxide concentration and total pressure. The rateconstant was determined to be 1.9±0.1 × 1011 12/mol2.sec at 298°K, with a high-pressure limit of 9.3 ± 2.1×109 l/mol·sec-1. The observed kinetics are consistent with a termolecular energy transfer mechanism.

Notes: The title reaction has been investigated in the temperature range 667-715K. The only reaction products were trifluorosilyl iodide and hydrogen iodide. The rate law \documentclass{article}\pagestyle{empty}\begin{document}$$ - \frac{{d\left[{{\rm I}_2} \right]}}{{dt}} = \frac{{k\left[{{\rm I}_2} \right]^{1/2} \left[{{\rm F}_3 {\rm SiH}} \right]}}{{1 + k\prime \left[{{\rm HI}} \right]/\left[{{\rm I}_2} \right]}} $$\end{document} was obeyed over a wide range of iodine and trifluorosilane pressures. This expression is consistent with an iodine atom abstraction mechanism and for the step \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm I}^ \cdot + {\rm F}_3 {\rm SiH}\mathop {\longrightarrow}\limits^1 {\rm F}_3 {\rm Si}^\cdot + {\rm HI} $$\end{document} log k1(dm3/mol·sec) = (11.54 ± 0.17) - (130.5 ± 2.2 kJ/mol)/RT In 10 has been deduced. From this the bond dissociation energy D(F3Si—H) = (419 ± 5) kJ/mol (100.1 kcal/mol) is obtained. The kinetic andthermochemical implications of this value are discussed.

Notes: The recombination of bromine atoms at room temperature has been studied by flash photolysis in the range of 1-100 atm of the inert diluent He, leading to a value for the third-order rate constant of (1.5 ± 0.2) × 1015 cm6/mol2.sec. In the presence of NO the recombination is considerably accelerated. The falloff curve of the recombination Br + NO (+He) → BrNO (+He) was also measured resulting in a value for the limiting low-pressure rate constant of (3.4 ± 1.3) × 1015 cm6/mol2.sec. In experiments with excess NO, rate constants of (2.2 ± 1) × 1014 cm3/mol·sec for the reaction Br + BrNO → Br2 + NO, and (6.1 ± 0.4) × 109 cm6/mol2.sec for the reaction Br2 + 2NO → 2BrNO were obtained.

Notes: A previously developed model for active species concentration profiles in infinite cylindrical systems has been extended to include the spherical system. The model couples the processes of diffusion to and reaction at the wall. Predictions of time buildup under conditions of homogeneous production by light, and time decay after extinguishing the light source, are made for H atoms. Such predictions require a knowledge of the wall recombination coefficient and the binary diffusion coefficient for H in heat bath gas. The model is experimentally tested by measuring the first-order decay constants of H at room temperature in various pressures (10-1500 torr) of six heat bath gases. The atomic concentration is monitored by Lyman-α absorption photometry. The results show good agreement with model predictions in the various heat bath gases up to ∼400 torr and depend only on one parameter,γ, the recombi-nation coefficient. This should be contrasted with the earlier work where slight variation in γ was invoked. The rate constants at pressures higher than 400 torr are consistently higher than model predictions.

Notes: Atomic resonance absorption spectrometry with a nonreversed fluorine resonance lamp (∼95 nm) has been used to study the kinetics of elementary reactions of ground state F2PJ atoms in a discharge-flow system. The following rate constants (in cm3/molec·sec)All rate constants are given with 1.5 σ. were determined at 298° K: The reaction F 2PJ + HCl(1) was found to give J-excited Cl 2P1/2 atoms with a product branching ratio [Cl 2P1/2]/[Cl 2P3/2] = 0.10.

Notes: Equations for the average energy of chemically activated species are developed, and uncertainties in the various energy quantities involved are discussed. Various approaches to the energy distribution function of chemically activated species are discussed. Trial calculations on methylcyclobutane are presented.

Notes: The hydrogen-atom recombination reaction has been simulated using a molecular dynamics technique recently formulated by the authors [1]. The rate of recombination has been calculated over a range of temperatures and inert gas concentrations (He and Ar) and agrees well with available experimental data. The calculations reproduce the negative activation energy characteristic of an atom recombination process. Over the range of conditions studied recombination was found to proceed via the energy transfer mechanism only, no evidence of bound HAr or HHe species was observed. Recombination was found to occur through an intermediate metastable diatomic molecule which is in equilibrium with its environment and from which there is a bottleneck to the formation of a stable molecule. The initial formation of a metastable species is sensitive to the hydrogen-inert gas potential, but relaxation of the total energy is primary determined by the mass of the third-body and the collision frequency.

Notes: The title reaction, displaying peculiar characteristics as to relative rates and isomer distributions, has been studied in detail. Prior to this study, different mechanisms had been advanced by several groups. Kinetic features (isomer patterns, relative and absolute rates, reaction orders, influences of additives, H/D isotope effects) strongly point to a free-radical (chain) process, in which (1) is a crucial step. This abstraction reaction, endothermal by about 6 kcal/mol, apparently proceeds via a transition state closely resembling the free aryl radical. Relative rates and isomer distributions therefore reflect differences in stabilization energies, or in DH°(Ar - H). With high arene-Cl2 intake ratios or, more pronounced, with CCl4 as the reagent, aryl radicals also lead to biaryl, where arene successfully competes with the halogenating agent. This interpretation is quantitatively supported by our observation that “added,˝” recognizable aryl radicals yield the same chlorination-arylation product ratio, and by the results of competitive chlorination of benzene and chloroform over a temperature range of 200°C, where the latter study substantiates the value DH0(C6H5 - H) ≈ 109 kcal/mol.

Notes: The pyrolysis of ethylene-butene-2 mixtures has been studied in a static system over the temperature range of 689°-754°k and for initial pressures of each olefin of 20-200 torr. The two main addition products were cyclopentene and 3-methylpentene-1. Kinetic evidence indicated that cyclopentene was formed from radical processes while 3-methylpentene-1 was formed by the molecular “ene¨” addition of ethylene to butene-2 through a six-center transition state. The following rate constants were obtained: The pyrolysis of 3-methylpentene-1 has been studied over the same temperature range and for initial pressures of 20-100 torr. Kinetic evidence showed that the products ethylene and butenes were formed in both radical and molecular processes. Estimates of the rate constant k-1t and k-1c were, however, in reasonable agreement with the measurements of k1t and k1c. The mechanism of the ene reaction is discussed, and it is concluded that the transition state does not involve the formation of a biradical.

Notes: The pyrolysis of ethylene-propylene and ethylene-isobutene mixtures has been studied in a static system over the temperature range of 682°-754° K and for initial pressures of each olefin of 33-300 torr. The following molecular ene reactions were observed and the rate constants measured: Using thermodynamic data, rate constants for the corresponding retro-ene decomposition reactions were calculated and compared to kinetic data reported for similar compounds. Other products were formed by radical chain processes, the main higher molecular weight ones being cyclopentene and 1-methylcyclopentene. A mechanism involving addition of allyl radicals is suggested for the formation of these products.

Notes: A program system is described for the integration of the rate equations resulting from large systems of elementary reactions. The Gear integration method is used for this problem, which frequently may exhibit stiffness instability when other integration methds are employed. No usage of the quasi-steady-state approximation is necessary. Ease in varying the reaction mechanism and simplicity of input structure are coupled with efficient execution and minimal demands for program storage as key features. The input-output structure, method of operation, and implementation are summarized, along with core storage requirements and execution times for trials using an IBM 360/44 computer.

Notes: The thermal reaction of 2-pentene (cis or trans) has been performed in a static system over the temperature range of 470°-535°C at low extent of reaction and for initial pressures of 20-100 torr. The main products of decomposition are methane and 1,3-butadiene. Other minor primary products have been monitored: trans-2-pentene, trans- and cis-2-butenes, ethane, 1,3-pentadienes, 3-methyl-1-butene, propylene, 1-butene, hydrogen, ethylene, and 1-pentene. The initial orders of formation, 0.8-1.1 for most of the products and 1.5-1.8 for 1-pentene, increase with temperature. The formation of the products and the influence of temperature on their orders can be essentially explained by a free radical chain mechanism. But cis-trans or trans-cis isomerization and hydrogen elimination from cis-2-pentene certainly involve both molecular and free radical processes. The formation of 1-pentene mainly occurs from the abstraction of the hydrogen atom of 2-pentene by resonance stabilized free radicals (C5H9.).

Notes: The kinetics of the thermal bromination reaction have been studied in the range of 261°-391°C. The observed rate law is compatible with initiation by the step for which we obtain \documentclass{article}\pagestyle{empty}\begin{document}$$ \log k_6 (cm^3 /mol - \sec) = (13.41 \pm 0.26) - (11700 \pm 700)/\theta $$\end{document} where Θ = 2.303RT cal/mol. Using the above value of E6, we have \documentclass{article}\pagestyle{empty}\begin{document}$$ {D(C}_{\rm 6} {\rm F}_{{\rm 5}^{\rm -}} {\rm I)} \to {\rm 53.5}\ {\rm kcal/mol} $$\end{document}This result disagrees with values of D(C6F5-I) obtained in other ways and we conclude that reaction (3) probably does not involve initiation by reaction (6). Instead, initiation may involve an addition of Br to the ring in C6F5I followed by decomposition of the adduct to give C6F5Br. If correct, this implies that the Arrhenius parameters above refer to the addition reaction rather than to reaction (6).

Notes: The rate constants and modes of reaction of NO2+ and C2H5ONO2NO2+ with aromatic compounds and alkanes have been determined in a pulsed ion cyclotron resonance mass spectrometer. Both ions undergo competing charge transfer and substitution reactions (NO2+ + M → MO+ + NO; C2H5ONO2NO2+ + M → MNO2+ + C2H5ONO2) with aromatic molecules. In both cases, the probability that a collision results in charge transfer increases with increasing exothermicity of that process. The C2H5ONO2NO2+ ion does not undergo charge transfer with molecules having an ionization potential greater than about 212 kcal/mol (9.2 eV); this observation leads to an estimate of 13 kcal/mol for the binding energy between NO2+ and C2H5ONO2. The importance of the substitution reaction depends on the number of substituents on the aromatic ring and the molecular structure, and, in the case of C2H5ONO2NO2+ ions, on the energetics of the competing charge transfer process. Both NO2+ and C2H5ONO2NO2+ undergo hydride transfer reactions with alkanes. For both these ions, k(hydride transfer)/k (collision) increases with increasing exothermicity of reaction, but in both cases the rate constants of reaction are unusually low when compared with other hydride transfer reactions of comparable exothermicity which have been reported in the literature. This is interpreted as evidence that the attack on the alkane preferentially involves the nitrogen atom (where the charge is localized) rather than one of the oxygen atoms of NO2+.

Notes: A general competitive method is described for the study of the kinetics of the reactions of radicals with halogens and interhalogen compounds in the gas phase. The method is applied to the reactions over the temperature range of 48°-199°C. It is found that \documentclass{article}\pagestyle{empty}\begin{document}$$ \log (k_6 /k_5) = \log (k_\varepsilon /k_7) = (- 0.042 \pm 0.060) - (8700 \pm 1300)/\theta $$\end{document} where Θ=2.303RT J/mol. Also \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{l} A_7 = 1/2A_{5,} \,\,\,\,\,\,\,\,\,\,\,\,E_7 = E_5 \\ A_8 = 1/2A_{6,} \,\,\,\,\,\,\,\,\,\,\,\,E_8 = E_6 \\ \end{array} $$\end{document}There is no correlation between differences in activation energies and differences in enthalpy changes for these reactions, but polar effects may be important in reactions (7) and (8).

Notes: 4-Methylhexyne-1, 5-methylhexyne-1, hexyne-1, and 6-methylheptyne-2 have been decomposed in comparative-rate single-pulse shock-tube experiments. Rate expressions for the initial decomposition reactions at 1100°K and from 2 to 6 atm pressure are \documentclass{article}\pagestyle{empty}\begin{document}$$ k({\rm HC} \equiv {\rm CCH}_{{\rm 2}^{{\rm -}}}s {\rm C}_{\rm 4} {\rm H}_{\rm 9} \to {\rm HC} \equiv {\rm CCH}_{\rm 2} \cdot + s{\rm C}_{\rm 4} {\rm H}_{\rm 9} \cdot) = 10^{15.9} \exp (- 35,000/T)\sec ^{- 1} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k({\rm HC} \equiv {\rm CCH}_{{\rm 2}^{{\rm -}}}i {\rm C}_{\rm 4} {\rm H}_{\rm 9} \to {\rm allene} + n{\rm C}_{\rm 4} {\rm H}_{\rm 8}) = 10^{12.9} \exp (- 28,000/T)\sec ^{- 1} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k({\rm HC} \equiv {\rm CCH}_{{\rm 2}^{{\rm -}}}i {\rm C}_{\rm 4} {\rm H}_{\rm 9} \to {\rm HC} \equiv {\rm CCH}_{\rm 2} \cdot + i{\rm C}_{\rm 4} {\rm H}_{\rm 9} \cdot) = 10^{16.1} \exp (- 36,700/T)\sec ^{- 1} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k({\rm HC} \equiv {\rm CCH}_{{\rm 2}^{{\rm -}}}i {\rm C}_{\rm 4} {\rm H}_{\rm 9} \to {\rm allene} + i{\rm C}_{\rm 4} {\rm H}_{\rm 8}) = 10^{2.3} \exp (- 27,500/T)\sec ^{- 1} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k({\rm HC} \equiv {\rm CCH}_{{\rm 2}^{{\rm -}}}n {\rm C}_{\rm 3} {\rm H}_{\rm 7} \to {\rm HC} \equiv {\rm CCH}_{\rm 2} \cdot + n{\rm C}_{\rm 3} {\rm H}_{\rm 7} \cdot) = 10^{15.9} \exp (- 36,300/T)\sec ^{- 1} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k({\rm HC} \equiv {\rm CCH}_{{\rm 2}^{{\rm -}}}n {\rm C}_{\rm 3} {\rm H}_{\rm 7} \to {\rm allene} + n{\rm C}_{\rm 3} {\rm H}_{\rm 6}) = 10^{12.7} \exp (- 28,400/T)\sec ^{- 1} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k({\rm CH}_3 {\rm C} \equiv {\rm CCH}_{2^{-}}i {\rm C}_4 {\rm H}_9 \to {\rm CH}_3 {\rm C}) \equiv {\rm CCH}_{\rm 2} \cdot + i{\rm C}_{\rm 4} {\rm H}_{\rm 9} \cdot) = 10^{16.2} \exp (- 36,800/T)\sec ^{- 1} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k({\rm CH}_3 {\rm C} \equiv {\rm CCH}_{2^{-}}i {\rm C}_4 {\rm H}_9 \to 1,2-butadiene + i{\rm C}_{\rm 4} {\rm H}_{\rm 8}) = 10^{12.3} \exp (- 28,700/T)\sec ^{- 1} $$\end{document} In combination with previous results, rate expressions for propargyl C—C bond cleavage are related to that for the alkanes by the expression \documentclass{article}\pagestyle{empty}\begin{document}$$ k_{\rm B} (alkyne) = \frac{1}{{3 \pm 1.5}}\exp (+ 4.25/T)k_{\rm B} (alkane) $$\end{document} These results yield a propargyl resonance energy of D(nC3H7-H) - D(C3H3-H) = 36 ± 2 kJ, in excellent agreement with a previous shock-tube study. They also lead to D(CH3C≡CCH2-H) - D(C3H3-H) = 0.6 ± 3 kJ, D(sC4H9-H) - D(iC3H7-H) = 0 ± 3 kJ, D(iC4H9-H) - D(nC3H7-H) = 2 ± 3 kJ, and D(nC3H7-H) - D(iC3H7-H) = 13.9 ± 3 kJ (all values are for 300°K). The systematics of the molecular decomposition process are explored.

Notes: The reactions of hydroxyl radicals with eight substituted aromatic hydrocarbons and four olefins were studied utilizing the flash photolysis-resonance fluorescence technique. The rate constants were measured at 298°K using either Ar or He as the diluent gas. The values of the rate constants (k × 1012) in the units of cm3/molec. sec are (a) OH + o-xylene → products: (12.9±3.8), 20 torr He; (13.0±0.3), 20 torr Ar; (12.4±0.1), 200 torr He;(b) OH + m-xylene → products: (15.6±1.4), 3 torr Ar; (19.4±0.8), 20 torr Ar; (21.4±0.2), 20 torr He; (20.3±1.9), 200 torr Ar; (20.6±1.3), 200 Torr He;(c) OH + p-xylene → products: (8.8±1.2), 3 torr Ar; (10.1±1.0), 20 torr He; (10.5±0.6), 200 torr He;(d) OH + ethyl benzene → products: (7.50±0.38), 3 torr He; (7.06±0.26), 20 torr He; (7.95±0.28), 200 torr He;(e) OH + n-propylbenzene → products: (6.40±0.36), 20 torr He; (5.86±0.16), 200 torr He;(f) OH + isopropylbenzene → products: (7.79±0.40), 200 torr He;(g) OH + hexafluorobenzene → products: (0.221±0.020), 20 torr He; (0.219±0.016) 200 torr He;(h) OH + n-propyl pentafluorobenzene → products: (2.52±0.54), 3 torr He; (3.01±0.76), 20 torr He; (3.06±0.24), 200 torr He;(i) OH + propylene → products: (25.6±1.2), 20 torr He; (26.3±1.2), 200 torr He;(j) OH + 1-butene → products: (29.6±1.9), 3 torr He; (29.4±1.4), 20 torr He;(k) OH + cis-2-butene → products: (43.2±4.1), 3 torr He; (42.6±2.5), 20 torr He;(l) OH + tetramethylethylene → products: (56.9±1.3), 20 torr He.

Notes: The first-order kinetics and hydrogen kinetic isotope effect of the decarboxylation of oxalic acid in acetophenone were studied in the temperature range of 109.6°-150.0°C. The rate constants, activation parameters, and hydrogen kinetic isotope effect were calculated. Detailed comparison and discussion of the results were made with the data reported in the literature. Kinetic isotope effects and solvent effects on rates should be considered similar in mechanistic and/or theoretical studies in the sense that kinetic isotope effects result from a small perturbation of the reaction coordinate, while the solvent effect causes a general overall variation on the potential energy surface (thereby resulting in a change in the reaction coordinate).

Notes: The mechanism of the photolysis of formaldehyde was studied in experiments at 3130 Å and in the pressure range of 1-12 torr at 25°C. The experiments were designed to establish the quantum yields of the primary decomposition steps (1) and (2), CH2O + hν → H + HCO (1): CH2O + hν → H2 + CO (2), through the effects of added isobutene, trimethylsilane, and nitric oxide on ΦCO and ΦH2. The ratio ΦCO/ΦH2 was found to be 1.01 ± 0.09(2σ) and (ΦH2 + ΦCO)/2 = 1.10 ± 0.08 over the range of pressures and a 12-fold change in incident light intensity. Isobutene and nitric oxide additions reduced ΦH2 to about the same limiting value, 0.32 ± 0.03 and 0.34 ± 0.04, respectively, but these added gases differed in their effects on ΦCO. With isobutene addition ΦCO/ΦH2 reached a limiting value of 2.3; with NO addition ΦCO exceeded unity. The addition of small amounts of Me3SiH reduced ΦH2 to 1.02 ± 0.08 and lowered ΦCO to 0.7. These findings were rationalized in terms of a mechanism in which the “nonscavengeable,” molecular hydrogen is formed in reaction (2) with φ2 = 0.32 ± 0.03, while the “free radical” hydrogen is formed in reaction (1) with φ1 = 0.68 ± 0.03. In the pure formaldehyde system these reactions are followed by (3)-(5): H + CH2O → H2 + HCO (3); 2HCO → CH2O + CO (4); 2HCO → H2 + 2CO (5). The data suggest k4/k5 ≅ 5.8. Isobutene reduced ΦH2 by the reaction H + iso-C4H8 → C4H9 (20), and the results give k20/k3 ≅ 43 ± 4, in good agreement with the ratio of the reported values of the individual constants k3 and k20.

Notes: The oxidative cleavage of some aliphatic ketoximes by thallium(III) acetate was studied in the temperature range of 20-40°C. The reactions were followed by determination of the rates of disappearance of thallium(III) acetate for variations in [substrate], [Tl(III)], [H+], ionic strength, temperature, etc. The reactions were found to be totally second order-first order with respect to each reactant. The second-order rate constants and thermodynamic parameters were evaluated and discussed. The mechanism proposed involves one-electron oxidation to the iminoxy radical followed by an another one-electron oxidation to the hydroxynitroso compound which dimerizes and decomposes to give the carbonyl compounds and hyponitrous acid.

Notes: The rate of disappearance of C2N2 in the presence of a large excess of H atoms has been measured in a discharge-flow system at pressures near 1 torr and temperatures in the range of 282-338 K. Under these conditions the reaction has a small negative temperature coefficient. A transition from second-order to third-order kinetics with decreasing pressure occurs at pressures near 1 torr. The results are discussed in terms of the mechanism where k7 = (1.5 ± 0.2) × 10-15 cm3/molec1·sec is found for the forward rate of reaction (7). The results also give k7k8/k-7 = 3.7 × 10-31 cm6/molec2·sec and k7k9/k-7 = 3.0 × 10-32 cm6/molec2·sec, the first being probably an upper limit and the second probably a lower limit; hence k8/k9 = 12 is found as an upper limit.

Notes: Oxidative kinetics of diethyl ketone in perchloric acid media in the presence of mercuric acetate have been studied by using N-bromosuccinimide (NBS) as oxidant in the temperature range of 25°-50°C. It has been found that the order with respect to NBS is zero while with respect to diethyl ketone and [H+], it is unity. Succinimide, sodium perchlorate, and mercuric acetate have an insignificant effect on the reaction rate, while the dielectric effect was negative. A solvent isotope effect (k0D2O/k0H2O = 1.6-1.8) at 35°C has been observed. On the basis of the available evidences a suitable mechanism consistent with the experimental results has been proposed in which it is suggested that the mechanistic route for NBS oxidation in an acidic medium is through the enol form of the ketone. The magnitude of the solvent effect also supports the mechanism. Various activation parameters have been calculated, and the 1,2-dicarbonyl compound has been identified as the end product of the reaction.

Notes: The oxidation of substituted benzyl alcohols by bis(2,2′-bipyridyl) copper(II) permanganate (BBCP), leading to the corresponding benzaldehydes is first-order with respect to BBCP. Michaelis-Menten type kinetics were observed with respect to the alcohols. The oxidation of a,a-dideuteriobenzyl alcohol indicated the presence of a substantial kinetic isotope effect. The rates of oxidation of meta- and para-substituted benzyl alcohols were correlated in terms of Charton's triparametric LDR equation whereas ortho- substituted benzyl alcohols were correlated with a four parametric LDRS equation. The results of correlation analyses point to an electron-deficient reaction center in the transition state. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 9-16, 1997.

Notes: By conducting an excimer laser photolysis (193 and 248 nm) behind shock waves, three elementary reactions important in the oxidation of H2S have been examined, where, H, O, and S atoms have been monitored by the atomic resonance absorption spectrometry. For HS + O2 → products (1), the rate constants evaluated by numerical simulations are summarized as: k1 = 3.1 × 10-11exp|-75 kJ mol-1/RT| cm3molecule-1s-1 (T = 1400-1850 K) with an uncertainty factor of about 2. Direct measurements of the rate constants for S + O2 → SO + O (2), and SO + O2 → SO2 + O (3) yield k2 = (2.5 ± 0.6) × 10-11 exp|-(15.3 ± 2.5) kJ mol-1/RT| cm3molecule-1s-1 (T = 980-1610 K) and, k3 = (1.7 ± 0.9) × 10-12 exp|-(34 ± 11) kJ mol-1/RT| cm3molecule-1s-1 (T = 1130-1640 K), respectively. By summarizing these data together with the recent experimental results on the H(SINGLE BOND)S(SINGLE BOND)O reaction systems, a new kinetic model for the H2S oxidation process is constructed. It is found that this simple reaction scheme is consistent with the experimental result on the induction time of SO2 formation obtained by Bradley and Dobson. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 57-66, 1997.

Notes: Rate constants have been measured for the reaction of OH radicals with four amides, R1N(CH3) - C(O)R2 (R1 = H or Methyl, R2 = Methyl or Ethyl), at 300 and 384 K using flash photolysis/resonance fluorescence. Reactants are introduced under slow flow conditions and are controlled by two independent methods, gas saturation and continuous injection. It turns out that the reactivities of the amides are considerably lower than those of the corresponding amines. The pattern of rate constants obtained at 300 K: 14, 21, 5.2, and 7.6 · 10-12 cm3/s for N,N-Dimethylacetamide (dmaa), N,N-Dimethylpropionamide (dmpa), N-Methylacetamide (maa), and N-Methylpropionamide (mpa), respectively, indicates a single, dominating reaction center and strong electronic effects of the substituents at both sides of the amide function. Correspondingly, the observed negative temperature dependence (E/R = - 400 to - 600 K) excludes a direct abstraction mechanism. © 1997 John Wiley & Sons, Inc.

Notes: The kinetics of the reactions between sodium nitrite and phenol or m-, o-, or p-cresol in potassium hydrogen phthalate buffers of pH 2.5-5.7 were determined by integration of the monitored absorbance of the C-nitroso reaction products. At pH 〉 3, the dominant reaction was C-nitrosation through a mechanism that appears to consist of a diffusion-controlled attack on the nitrosatable substrate by NO+/NO2H2+ ions followed by a slow proton transfer step; the latter step is supported by the observation of basic catalysis by the buffer which does not form alternative nitrosating agents as nitrosyl compounds. The catalytic coefficients of both anionic forms of the buffer have been determined. The observed order of substrate reactivities (o-cresol ≈ m-cresol 〉 phenol ≫ p-cresol) is explained by the hyperconjugative effect of the methyl group in o- and m-cresol, and by its blocking the para position in p-cresol. Analysis of a plot of ΔH# against ΔS# shows that the reaction with p-cresol differs from those with o- and m-cresol as regards the formation and decomposition of the transition state. The genotoxicity of nitrosatable phenols is compared with their reactivity with NO+/NO2H2+. © 1997 John Wiley & Sons, Inc.

Notes: For a number of hydrofluorocarbons (HFCs), EHez has been found to have a linear correlation with each of the following: (i) log (k/n); (ii) A/n; and (iii) Ea/R, where EH = HOMO energy of the molecule, z = average fractional positive charge on the abstractable hydrogen atom in the molecule, k = rate constant of the gas-phase H abstraction reaction of the molecule with OH radical at 298 K, n = number of abstractable H atoms in the molecule, A = preexponential factor, and Ea/R = activation temperature of the said reaction. These correlations have been used to estimate the temperature dependent rate constants for the reactions of OH radical with CF3CF2CH2CH2CF2CF3, CF3CH2CF2CH2CF3, CF3CF2CH2CH2F, CF3CH2CH3, CF3CH2CHF2, CF3CHFCH2F, and CHF2CHFCHF2 as {6.97 × 10-13 exp(1481/T)}, {5.43 × 10-13 exp(1754/T)}, {7.95 × 10-13 exp(l308/T)}, {8.0 × 10-13 exp(1300/T)}, {7.03 × 10-13 exp(1470/T)}, {7.33 × 10-13 exp(1417/T)}, and {8.09 × 10-13 exp(1285/T)}, respectively. These have not yet been measured experimentally. Linear correlation between EHez and log (k/n) has also been observed for nine halogen substituted acetaldehydes. On the other hand, EH is found to have a better linear correlation with log (k/n) than EHez in the case of fluorinated ethers and alcohols where the available experimental data are at present limited. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 187-194, 1997.

Notes: The reaction between the radical cation derived from 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and phenols follows a kinetic law given by \documentclass{article}\pagestyle{empty}\begin{document}$$ d[ABTS^{\buildrel{+}\over{\cdot}}]/dt=k [ABTS^{\buildrel{+}\over{\cdot}}]^2[PhOH]/[ABTS] $$\end{document} with stoichiometric coefficients between one and two. The rate constant is almost unrelated to the structure of the phenol, while the number of ABTS radicals scavenged by each phenol molecule increases with para-substitution. These results are explained in terms of a fast, reversible electron transfer \documentclass{article}\pagestyle{empty}\begin{document}$$ ABTS^{\buildrel{+}\over{\cdot}}\,+PhOH {\buildrel{\longrightarrow}\over{\longleftarrow}} ABTS + PhO\bullet+H^{+} $$\end{document} followed by the self-combination of the phenoxy radicals and/or their reaction with another ABTS derived radical action. The relative rate of these processes determine the value of the stoichiometric coefficient. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 219-224, 1997.

Notes: A continuous flow-through reactor with a thin layer of solid particles (size ranging from 100 to 300 μm) was used to obtain a deeper knowledge on the mechanism of dissolution of UO2 under oxidizing conditions. Using this methodology the dissolution rate of uranium dioxide was determined at three different oxygen partial pressures (5, 21, and 100% in nitrogen) and as a function of pH (between 3 and 12) in a noncomplexing medium.From the results of these experiments the following rate equation was derived: \documentclass{article}\pagestyle{empty}\begin{document}$$ (3 〈 pH 〈 6.7)\,r\,(mol\cdot s^{-1}\cdot m^{-2})\,=\,(3.5 \pm 0.8) \cdot 10^{-8} \cdot [H^{+}]^{0.37\pm 0.01}\cdot[O_2]^{0.31\pm 0.02} $$\end{document} In addition, XPS characterizations were performed to determine the U(IV)/U(VI) ratio on the solid surface at different experimental times and conditions. These results showed that at acidic conditions (pH below 6.7) the final solid surface presents a stoichiometry close to UO2, while at alkaline conditions the final solid surface average composition is close to UO2.25. This information was integrated with the results of the leaching experiments to present a model for the mechanism of dissolution of uranium dioxide under the experimental conditions. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 261-267, 1997.

Notes: The kinetics of the gas-phase reactions of OH radicals, NO3 radicals, and O3 with indan, indene, fluorene, and 9,10-dihydroanthracene have been studied at 297 ± 2 K and atmospheric pressure of air. The rate constants, or upper limits thereof, for the O3 reactions were (in cm3 molecule-1 s-1 units): indan, 〈 3 × 10-19; indene, (1.7 ± 0.5) × 10-16, fluorene, 〈 2 × 10-19; and 9,10-dihydroanthracene, (9.0 ± 2.0) × 10-19. Using a relative rate method, the rate constants for the OH radical and NO3 radical reactions, respectively, were (in cm3 molecule-1 s-1 units): indan, (1.9 ± 0.5) × 10-11 and (6.6 ± 2.0) × 10-15; indene, (7.8 ± 2.0) × 10-11 and (4.1 ± 1.5) × 10-12; fluorene, (1.6 ± 0.5) × 10-11 and (3.5 ± 1.2) × 10-14; and 9,10-dihydroanthracene, (2.3 ± 0.6) × 10-11 and (1.2 ± 0.4) × 10-12. These kinetic data were used to assess the relative contributions of the various reaction pathways. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 299-309, 1997.

Notes: A laser-flash photolysis/UV absorption technique has been used to study the temperature dependence (from T = 300 - 470 K) of the self-reaction kinetics of representative primary secondary and tertiary β-hydroxyperoxy radicals \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{lclr} 2\,\rm{HOCH}_2\rm{CH}_2\rm{O}_2 & \longrightarrow & 2\,\rm{HOCH}_2\rm{CH}_2\rm{O}\,+\,\rm{O}_2 & (1\rm{a})\\ & \longrightarrow & \rm{HOCH}_2\rm{CH}_2\rm{OH}\,+\rm{HOCH}_2\rm{CH}_2\rm{O}\,+\,\rm{O}_2 & (1\rm{b})\\ 2\,\rm{HOCH}(\rm{CH}_3)\rm{CH}(\rm{CH}_3)\rm{O}_2 & \longrightarrow & 2\,\rm{HOCH}(\rm{CH}_3)\rm{CH}(\rm{CH}_3)\rm{O}\,+\,\rm{O}_2 & (2\rm{a})\\ & \longrightarrow & \rm{HOCH}(\rm{CH}_3)\rm{CH}(\rm{CH}_3)\rm{OH} & \\ & &+\rm{HOCH}(\rm{CH}_3)\rm{CH}(\rm{CH}_3)\rm{O}+\rm{O}_2 & (2\rm{b})\\ 2\,\rm{HOC}(\rm{CH}_3)_2\rm{C}(\rm{CH}_3)_2\rm{O}_2 & \longrightarrow & 2\,\rm{HOC}(\rm{CH}_3)_2 \rm{C}(\rm{CH}_3)_2\rm{O}\,+\,\rm{O}_2 & (3)\\ \end{array} $$\end{document} The following Arrhenius expressions were derived for the rate coefficients of reactions (1)-(3) (in cm3 molecule -1s-1) and for the product branching ratios of reactions (1) and (2) as a function of temperature (all errors 1σ) \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{l}k_1=(6.9_{+2.1}^{-1.5})\times 10 ^{-14}\,\exp[(1040\pm 100)/\rm{T}]\\ \beta_1=(3100_{+3700}^{-1700})\,\exp[(-2400\pm 280)/\rm{T}] (\hbox{ where } \beta_1=k_{1a}/k{1\rm{b}})\\ k_2=(7.7_{+12.8}^{-4.8})\times 10 ^{-15}\,\exp[(1330\pm 350)/\rm{T}]\\ \beta_2=(4.0_{+0.2}^{-0.1})\times 10 ^{4}\,\exp[(-3600\pm 100)/\rm{T}]\\ k_3=(4.7_{+6.5}^{-2.7})\times 10 ^{-13}\,\exp[(-1420\pm 320)/\rm{T}]\\ \end{array} $$\end{document} The calculated rate coefficients for reactions (1)-(3) at 298 K are therefore (in 10-13 cm3molecule -1s -1 23 ± 2, 6.7 ± 1.3, and 0.040 ± 0.012, respectively which compare well with the values measured elsewhere at this temperature using a similar technique. The product branching ratios and the Arrhenius parameters are compared with those for other substituted and unsubstituted peroxy radical self reactions. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 323-331, 1997

Notes: The gas-phase reactivities of W(a5DJ, a7S3) with N2O, SO2, and NO in the temperature range of 295-573 K are reported. Tungsten atoms produced by the photodissociation of W(CO)6. The tungsten atoms were detected by a laser-induced fluorescence technique. The removal rate constants for the 6s25d4 a5Dl states were found to be pressure dependent for all of the reactants. Removal rate constants for the 6s15d5 a7S3 state were found to be fast compared to the a5DJ states and often approached the gas kinetic rate constant. The reaction rates for all the states were found to be pressure independent with respect to the total pressure. Results are discussed in terms of the different electronic configurations of the states of tungsten © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 367-375 1997

Notes: Real-time kinetic measurements are reported for the Cl + CH3CO → CH2CO + HCl reaction. The experiments utilize infrared spectroscopy to determine the time dependence of the ketene formed via this reaction and of the CO produced from the subsequent rapid reaction between chlorine atoms and ketene. The reaction is investigated over a pressure range of 10-200 torr and a temperature range of 215-353 K. Within experimental error the rate constant under these conditions is k5a = (1.8 ± 0.5) × 10-10 cm3 s-1. We have also examined the Cl + CH2CO reaction and found it to have a rate constant of k6 = (2.5 ± 0.5) × 10-10 cm3 s-1 independent of temperature. © John Wiley & Sons, Inc. Int J Chem Kinet 29: 421-429, 1997.

Notes: The kinetics of oxidation of indigo carmine (IC) by N-sodio-N-bromotoluenesulfonamide or bromamine-T (BAT) in pH 5 buffer medium has been investigated at 30°C using spectrophotometry at 610 nm. The reaction rate shows dependencies of first-order on [IC]0 second-order on [BAT]0, fractional order on [H+], and inverse first-order on [ρ-toluenesulfonamide]. The addition of chloride and bromide ions, and the variation of ionic strength of the medium have no influence on the reaction rate. There is a negative effect of the dielectric constant of the solvent. Activation parameters have been calculated. A single-pathway mechanism for the reaction, consistent with the kinetic data, has been proposed. © John Wiley & Sons, Inc. Int J Chem Kinet 29: 453-459, 1997

Notes: The Cl- and Br- initiated oxidations of CHCl(DOUBLEBOND)CCl2 in 700 torr of air at 296 K have been studied using a Fourier transform infrared spectrometer. Rate constants k(Cl+CHCl(DOUBLEBOND)CCl2)=(7.2±0.8)×10-11 and k(Br+CHCl(DOUBLEBOND)CCl2)=(1.1±0.4)×10-13 cm3 molecule-1 s-1 were determined using a relative rate technique with ethane and ethylene as references, respectively. The major products observed were CHXClC(O)Cl, (X=Cl or Br), CHClO, and CCl2O. Combining results obtained for the Cl-initiated oxidation of CHCl2(SINGLEBOND)CHCl2, we deduced that Cl-addition on trichloroethylene occurs via channel 1a, Cl+CHCl(DOUBLEBOND)CCl2→ CHCl2(SINGLEBOND)CCl2, (100±12)%. Self-reaction of the subsequently generated peroxy radicals CHCl2(SINGLEBOND)CCl2O2 leads to CHCl2CCl2O radicals which were found to decompose via channel 8a, CHCl2C(O)Cl+Cl, (91±11)% of the time, and channel 8b, CHCl2+CCl2O, (9±2)%. The reaction Br+CHCl(DOUBLEBOND)CCl2→CHBrCl(SINGLEBOND)CCl2 (17a) accounted for ≥(96±11)% of the total reaction. Decomposition of the CHBrCl(SINGLEBOND)CCl2O radicals proceeds (≥93±11)% via CHBrClC(O)Cl+Cl. As part of this work, k(Cl+CHCl2C(O)Cl)=(3.6±0.6)×10-14 and k(Cl+CHCl2(SINGLEBOND)CHCl2)=(1.9±0.2)×10-13 cm3 molecule-1 s-1 were measured. Errors reported above include statistical uncertainties (2σ) and estimated systematic uncertainties. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet: 29: 695-704, 1997.

Notes: The kinetics of oxidation of the aliphatic primary amines, n-propylamine, n-butylamine, and isoamylamine, by N-sodio-N-bromobenznesulfonamide or bromamine-B (BAB), in the presence of osmium(VIII), has been studied in alkaline medium at 35°C. In the presence of the catalyst, the experimental rate law for the oxidation of the amine substrate (S) takes the form, rate=k[BAB][OsO4][OH-]x, which in the absence of the catalyst changes to the form, rate=k[BAB][S][OH-]y, where x and y are less than unity. Additions of halide ions and the reduction product of BAB (benzenesulfonamide), and the variation of ionic strength of the solvent medium have no effect on the reaction rate. Activation parameters have been evaluated. The proposed mechanism assumes the formation of a complex intermediate between the active oxidant species, PhSO2NBr-, and the catalyst, OsO4, in the rate determining step. This complex then interacts with the substrate amine in fast steps to yield the end products. The average value for the deprotonation constant of monobromamine-B, forming PhSO2NBr-, is evaluated for the Os(VIII) catalyzed reactions of the three amines in alkaline medium as 9.80×103 at 35°C. The average value for the same constant for the uncatalyzed reactions is 1.02×104 at 35°C. © 1997 John Wiley & Sons, Inc.

Notes: Relative rate coefficients for the reaction of acetyl (CH3CO) radicals with O2 (k4) and Cl2 (k7) have been obtained at 298 K and 228 K as a function of total pressure, using FTIR/environmental chamber techniques. Measured values of k4/k7 were placed on an absolute basis using k7=2.8×10-11 exp(-47/T) cm3 molec-1 s-1. At 298 K, the value of k4 is constant ((7±2)×10-13 cm3 molec-1 s-1) at pressures from 0.1 to 2 torr, then increases to a high pressure limiting value of (3.2±0.6)×10-12 cm3 molec-1 s-1, which is approached at pressures above 300 torr. At 228 K, the low-pressure value of k4 increases by about 20-30%, while the high pressure value remains unchanged. Experiments designed to elucidate the products of reaction (4) as a function of pressure at 298 K indicate that the reaction occurs via a concerted mechanism in which CH3CO radicals combine with O2 to give an excited acetylperoxy radical (CH3COO2*) which is increasingly stabilized at high pressure at the expense of a low pressure decomposition channel. The yield of acetylperoxy radicals from reaction (4) decreases from 〉95% at pressures above 100 torr, to about 90% at 60 torr, and 50% at 6 torr. Indirect evidence for formation of OH radicals from the low pressure decomposition is presented, although the carbon-containing coproduct(s) of this channel could not be identified. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 655-663, 1997.

Notes: The sodium-hydrogen ion exchange constant for the system sodium 1-dodecanesulfonate-hydrochloric acid in aqueous acetonitrile has been determined from the pseudo-phase ion exchange model for surfactant catalytic effects. The results indicate that the micellar system behaves similarly for the aqueous and the aqueous acetonitrile (2.106 M) solvent systems.The influence of substrate molecular structure on micellar catalysis by perfluorooctanoic acid of the hydrolysis of hydroxamic acids (R - CO - NHOH) in aqueous acetonitrile has been explored. Data for substrate structures of fifteen compounds with R=alkyl, aralkyl, alicyclylalkyl, phenylalkyl, alkyl-substituted phenylalkyl, and with chain branching at the α, β, and γ positions are compared. Relative binding constant values indicate that substrates with aromatic groups are less well solubilized in the perfluoro micellar environment than are substrates with saturated groups.There is now evidence for specific micellar effects on the reaction rate as well as general micellar catalysis. © 1997 John Wiley & Sons, Inc.

Notes: It is shown experimentally that pentafluoroethane undergoes rapid protium-deuterium exchange with water in the presence of hydroxide ion. Addition of dimethylsulfoxide enhances the rate at least by a factor of 100. The first measured fractionation factor data are presented for the temperature range of 50-120°C. These values are compared with the theoretical estimations calculated by using isotopic reduced partition function ratios based on molecular vibrational frequencies. Although catalytic exchange is slow at ambient temperature, the reaction rate becomes measureable above around 60°C because of large activation energy (92 kJ/mole). Comparisons are made with similar data available for various halomethane and haloethane systems. © 1997 John Wiley & Sons, Inc.

Notes: Experimental kineticists are always faced with the problem of reducing kinetic data to extract physically meaningful information. A particularly vexing problem arises when different models reproduce the data but yield different values for the physical parameters. For over forty-five years Monte Carlo simulation techniques have been used to study the statistical behavior of parameters extracted from data. Not only do these simulations provide realistic uncertainties, correlation coefficients, and confidence envelopes, but they also provide insight into the nature of the model. These insights may be obtained by viewing two-dimensional scatter plots of the fractional changes of the parameters and one-dimensional histograms of the distributions of the changes in the parameters. Monte Carlo simulations are illustrated with examples from OH+CH4 → CH3+H2O and the high-pressure rate coefficient for methyl-methyl association. A more complex problem involves models for pressure-dependent rate coefficients in the falloff region. We have modeled methyl-methyl association with five of the most current analytic approximations for behavior in the falloff region. All of these reproduce the data to within their uncertainties. However, when Monte Carlo techniques are applied the correlations between the parameters and the nonlinear nature of their behavior become evident. We postulate that the statistical behavior of the parameters of a model may be used to distinguish one model from another and, thereby, identify those analytic approximations that hold promise for further investigation and utilization. Finally, the recent advent of high-speed workstations implies that Monte Carlo simulations should become a routine part of the analysis of kinetic data. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 803-817, 1997

Notes: Rate constants for three dimethylbenzaldehydes and two trimethylphenols have been determined for the OH reactions at 298±2 K and atmospheric pressure using a relative rate method. The OH reaction rate constants were placed on an absolute basis using the literature rate constant for 1,2,4-trimethylbenzene of (3.25±0.5)×10-11 cm3 molecule-1s-1). The measured rate constants were (in units of cm3 molecule-1 s-1) 2,4-dimethyl-benzaldehyde, (4.32±0.67)×10-11; 2,5-dimethylbenzaldehyde, (4.37±0.68)×10-11; 3,4-dimethylbenzaldehyde, (2.14±0.34)×10-11; and 2,3,5- trimethylphenol, (12.5±1.9)×10-11, 2,3,6-trimethylphenol, (11.8±1.8)×10-11. Using an average OH concentration of 8.7×105 molecule cm-3, the estimated atmospheric lifetimes are ca. 7.5 h for 2,4- and 2,5-dimethylbenzaldehydes, ca. 15 h for 3,4-dimethylbenzaldehyde, ca. 2.5 h for 2,3,5- and 2,3,6-trimethylphenols. The reactivities of the trimethylphenols exceed those of the dimethyl-benzaldehydes by more than a factor of 3. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 523-525, 1997.

Notes: The kinetics of the oxidation of formate, oxalate, and malonate by |NiIII(L1)|2+ (where HL1 = 15-amino-3-methyl-4,7,10,13-tetraazapentadec-3-en-2-one oxime) were carried out over the regions pH 3.0-5.75, 2.80-5.50, and 2.50-7.58, respectively, at constant ionic strength and temperature 40°C. All the reactions are overall second-order with first-order on both the oxidant and reductant. A general rate law is given as - d/dt|NiIII(L1)2+| = kobs|NiIII(L1)2+| = (kd + nks |R|)|NiIII(L1)2+|, where kd is the auto-decomposition rate constant of the complex, ks is the electron transfer rate constant, n is the stoichiometric factor, and R is either formate, oxalate, or malonate. The reactivity of all the reacting species of the reductants in solution were evaluated choosing suitable pH regions. The reactivity orders are: kHCOOH 〉 kHCOO-; kH2ox 〉 kHox- 〉 kox2-, and kH2mal 〉 kHmal- 〈 kmal2- for the oxidation of formate, oxalate, and malonate, respectively, and these trends were explained considering the effect of hydrogen bonded adduct formation and thermodynamic potential. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 225-230, 1997.

Notes: Na2(Mo2vO4EDTA).4H2O crystals have been prepared in pure form. Kinetics for the oxidation of the compound by S2O82- have been studied spectrophotometrically in dilute sulphuric acid medium. The effects of hydrogen ion concentration, metal ion concentration, S2O82- ion concentration, and temperature on the process have been studied. Rate equations have been derived to explain the experimental observations. On the basis of the observations, suitable mechanisms have been suggested. The kinetic parameters E*, ΔH≠, and ΔS≠ of the process have also been determined. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 269-274, 1997

Notes: The rates of gas-phase elimination reactions of methyl benzoylformate (1) and 3-hydroxy-3-methyl-2-butanone (2) were obtained at T = 600 K. The two substrates undergo unimolecular first-order elimination for which the Arrhenius equations are, respectively, log k = 13.2 - 53270/(4.574 × 600) for (1) and log k = 12.4 - 53060/(4.574 × 600) for (2). The products of pyrolysis of (1) are benzaldehyde, formaldehyde and CO, while those of (2) are acetaldehyde and acetone. The kinetics of the elimination reactions show benzoylformic acid to be 106-fold more reactive than (1), and pyruvic acid ca. 105-fold more reactive relative to (2); an indication of the rate-controlling part played by the acidity of the hydrogen atom involved in the elimination process of the present compounds in this particular type of reaction. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 295-298, 1997.

Notes: A differential method for analyzing first-order kinetic data is presented. While the essence of this approach has been known for almost a century, the use of computers to collect, store, and manipulate data has reenergized this innovative idea. Based on the equation ln |dA1/dt| = ln |k(Ao - A(infinity))| - kt, plots of ln |dAt/dt| vs. t were found to be lienar for both simulated kinetic data and data collected for the reaction of [(en)2Co(SCH2CH2NH2)]2+ with acrylamide. The rate constants for the reaction obtained by this method are identical to those obtained by the infinite-time method of analysis but do not require infinite-time measurements in their evaluation. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 333-338, 1997

Notes: Relative rate constant measurements have been carried out on the Cl-atom reactions with benzene, chlorobenzene, toluene, xylene, and styrene in 740 torr of air at room temperature (295 K), using the photochemical reactor-FTIR spectroscopy technique. The Cl atoms were generated by the UV photolysis of Cl2, and the reference compounds were CHF, Cl for benzene and chlorobenzene and isobutane for toluene xylene and styrene. Using the absolute rate constant for these two reference compounds reported in the literature, the following kinetic data were obtained for the study compounds (in units of cm3s-1). \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{ll} {\rm Benzene} & (1.3\pm 0.3)\times 10 ^{-15}\\ {\rm Chlorobenzen} & (9.8\pm 2.4)\times 10 ^{-16}\\ {\rm Toluene} & (5.9\pm 0.5)\times 10 ^{-11}\\ o-{\rm Xylene} & (1.5\pm 0.1)\times 10 ^{-10}\\ m-{\rm Xylene} & (1.4\pm 0.1)\times 10 ^{-10}\\ p-{\rm Xylene} & (1.5\pm 0.1)\times 10 ^{-10}\\ {\rm Styrene} & (3.6\pm 0.3)\times 10 ^{-10}\end{array} $$\end{document} The quoted error bars are for ± 2σ. The present kinetic results are compared with available literature data to update and expand the kinetics database for Cl-atom reactions of organic compounds. The results are also analyzed to provide insights into the reaction mechanism for the Cl-atom initiated oxidation of benzene under atmospheric conditions. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 349-358, 1997

Notes: The initiation reaction of the thermal decomposition of silicon tetrachloride \documentclass{article}\pagestyle{empty}\begin{document}$$ SiCl_4\,+\,M\,{\buildrel{k_1}\over{\longrightarrow}} SiCl_3\,+Cl\,+M \eqno(R1) $$\end{document} was studied behind reflected shock waves at temperatures between 1550 K and 2370 K and pressures between 1 and 1.5 bar. Atomic resonance absorption spectrometry (ARAS) was applied for time-resolved measurements of H atoms at the Lα-line in SiCl4/H2/Ar systems. Additional experiments were performed in the SiCl4/Ar system following the absorption of SiCl4 at the Lα-line. Rate coefficients for the reaction (RI) were determined to be: \documentclass{article}\pagestyle{empty}\begin{document}$$ k_1=4.8\times 10^{16}\exp(-40954 K/T) cm^3 mol^{-1} s^{-1}. $$\end{document} The choice between two possible alternatives of the first decomposition step, namely elimination of either Cl2 or Cl, has been made in favor of the second reaction on the basis of kinetic and energetic considerations. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 415-420, 1997.

Notes: Mixtures of cyclopentadiene diluted with argon were used to investigate its decomposition pattern in a single pulse shock tube. The temperatures ranged from 1080 to 1550 K and pressures behind the shock were between 1.7-9.6 atm. The cyclopentadiene concentrations ranged from 0.5 to 2%. Gas-chromatographic analysis was used to determine the product distribution. The main products in order of abundance were acetylene, ethylene, methane, allene, propyne, butadiene, propylene, and benzene. The decomposition of cyclopentadiene was simulated with a kinetic scheme containing 44 species and 144 elementary reactions. This was later reduced to only 36 reactions. The ring opening process of the cyclopentadienyl radical was found to be the crucial step in the mechanism. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 505-514, 1997.

Notes: Rate constants for the reactions of OH, NO3, and O3 with pinonaldehyde and the structurally related compounds 3-methylbutanal, 3-methylbutan-2-one, cyclobutyl-methylketone, and 2,2,3-trimethyl-cyclobutyl-1-ethanone have been measured at 300±5 K using on-line Fourier transform infrared spectroscopy. The rate constants obtained for the reactions with pinonaldehyde were: kOH=(9.1±1.8)×10-11 cm3 molecule-1 s-1, kNO3=(5.4±1.8)×10-14 cm3 molecule-1 s-1, and kO3=(8.9±1.4)×10-20 cm3 molecule-1 s-1. The results obtained indicate a chemical lifetime of pinonaldehyde in the troposphere of about two hours under typical daytime conditions, [OH]=1.6×106 molecule cm-3. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 527-533, 1997.

Notes: CF3O2CF3 was photolyzed at 254 nm in the presence of CO in 760 torr N2 or air at 296 K in a static reactor. In N2, the products CF3OC(O)C(O)OCF3 and CF3OC(O)O2C(O)OCF3 were detected by FTIR spectroscopy. In air, the only observed products were CF2O and CO2 and a chain process, initiated by CF3O, was invoked for the conversion of CO to CO2. From both product studies, a mechanism for the CF3O initiated oxidation of CO was derived, involving the addition reaction CF3O2 + CO → CF3OC(O). The rate constant for the reaction CF3O + CO at 296 K at a total pressure of 760 torr air was determined to be k(CF3O + CO) = (5.0 ± 0.9) × 10-14 cm3 molecule-1 s-1. © 1997 John Wiley & Sons, Inc.

Notes: The relative rate technique has been used to measure the hydroxyl radical (OH) reaction rate constant of ethyl 3-ethoxypropionate (EEP, CH3CH2(SINGLE BOND)O(SINGLE BOND)CH2CH2C(O)O(SINGLE BOND)CH2CH3). EEP reacts with OH with a bimolecular rate constant of (22.9±7.4)×10-12 cm3 molecule-1s-1 at 297±3 K and 1 atmosphere total pressure. In order to more clearly define EEP's atmospheric reaction mechanism, an investigation into the OH+EEP reaction products was also conducted. The OH+EEP reaction products and yields observed were: ethyl glyoxate (EG, 25±1% HC((DOUBLE BOND)O)C((DOUBLE BOND)O)(SINGLE BOND)O(SINGLE BOND)CH2CH3), ethyl (2-formyl) acetate (EFA, 4.86±0.2%, HC((DOUBLE BOND)O)(SINGLE BOND)CH2(SINGLE BOND)C((DOUBLE BOND)O)(SINGLE BOND)O(SINGLE BOND)CH2CH3), ethyl (3-formyloxy) propionate (EFP, 30±1%, HC((DOUBLE BOND)O)(SINGLE BOND)O(SINGLE BOND)CH2CH2(SINGLE BOND)C((DOUBLE BOND)O)(SINGLE BOND)O(SINGLE BOND)CH2CH3), ethyl formate (EF, 37±1%, HC((DOUBLE BOND)O)O(SINGLE BOND)CH2CH3), and acetaldehyde (4.9±0.2%, HC((DOUBLE BOND)O)CH3). Neither the EEP's OH rate constant nor the OH/EEP reaction products have been previously reported. The products' formation pathways are discussed in light of current understanding of oxygenated hydrocarbon atmospheric chemistry. © 1997 John Wiley & Sons, Inc.

Notes: Pseudo-first-order rate constants (k1 obs) for the reaction of MeNHOH with NCPH obey the relationship: k1 obs=k′b[MeNHOH]T2 where [MeNHOH]T represents total concentration of N-methylhydroxylamine buffer. The rate constants, k1 obs obtained at different total concentration of acetate buffer ([Buf]T) in the presence of 0.004 mol dm-3 MeNHOH follow the relationship: k1 obs=kb[Buf]T. The values of acetate buffer-catalyzed rate constant (kb) at different pH reveal the occurrence of both general base- and general acid- or general base-specific acid-catalysis in the reaction of MeNHOH with NCPH. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 647-654, 1997.

Notes: The temperature dependence of the rate coefficients for the OH radical reactions with iso-propyl acetate (k1), iso-butyl acetate (k2), sec-butyl acetate (k3), and tert-butyl acetate (k4) have been determined over the temperature range 253-372 K. The Arrhenius expressions obtained are: k1=(0.30±0.03)×10-12 exp[(770±52)/T]; k2=(109±0.14)×10-12 exp[(534±79)/T]; k3=(0.73±0.08)×10-12 exp[(640±62)/T]; and k4=(22.2±0.34)×10-12 exp[-(395±92)/T] (in units of cm3 molecule-1 s-1). At room temperature, the rate constants obtained (in units of 10-12 cm3 molecule-1 s-1) were as follows: iso-propyl acetate (3.77±0.29); iso-butyl acetate (6.33±0.52); sec-butyl acetate (6.04±0.58); and tert-butyl acetate (0.56±0.05). Our results are compared with the previous determinations and discussed in terms of structure-activity relationships. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet: 29: 683-688, 1997.

Notes: The processes of vibrational relaxation and unimolecular dissociation of the perfluoromethyl halides CF3Cl, CF3Br, and CF3I have been studied in the shock tube with the laser-schlieren technique. Vibrational relaxation was resolved in pure CF3Cl and CF3Br (400-484 K and 400-500 K, respectively), and in the mixtures; 2% CF3Cl/Kr (500-1000 K), 10% CF3Cl/Kr (440-670 K), 4% CF3Br/Kr (450-850 K), and 2% CF3I/Kr (620-860 K). Relaxation in the pure gases is extremely rapid, but shows a well-resolved, accurately exponential decay which provides very precise relaxation times in close agreement with ultrasonic results. Relaxation times as short as 0.1 μs-atm can be resolved, showing the method has a resolution within a factor 2-3 of the best ultrasonic methods. Relaxation dilute in rare gas shows a complex double exponential behavior consistent with a two-stage series process. Rates of CF3(SINGLEBOND)X fission in these mixtures were measured over 1800-3000 K, P〈0.55 atm, for CF3Cl; 1600-2500 K, P〈0.55 atm, in CF3Br; and 1260-2100 K, P〈0.34 atm, in CF3I. Rates for dissociation were derived from a full profile modeling using a secondary mechanism of six CF3 reactions. RRKM analysis showed all dissociations to lie near the low pressure limit. Using literature barriers, these rates are best fit with (ΔE)all=-270 cm-1 for CF3Cl, 〈ΔE〉down=0.3 T for CF3Br, and 〈ΔE〉down=800 cm-1 for CF3F. All these transfers are on the large side, similar to those found in other halogenated methanes. © 1997 John Wiley & Sons, Inc.

Notes: The temperature dependence of the rate constant for the exchange reaction between oxygen atoms and dioxygen molecules has been studied using the oxygen isotopes 16O and 18O. The reaction was studied by VIS-photolysis of ozone in the presence of isotopic dioxygen and with nitrogen as a bath gas at five different temperatures, 143 K, 173 K, 203 K, 253 K, and 295 K. High-resolution microwave spectroscopy was used to measure the composition of the ozone isotopomer mixtures and mass-spectrometry was used to determine the abundances of the isotopomeric dioxygen species formed during the reaction. The rate constant was determined to be kexchange=(2.66±0.78)×10-12 (T/300 K)-(0.88±0.26) cm3s-1 (±2σ) or as the ratio between rate constants for exchange and for ozone formation, (4.67±1.3)×1021 (T/300 K)(1.74±0.19) cm-3 (±2σ). © 1997 John Wiley & Sons, Inc.

Notes: The rate coefficient of the reaction CH+O2 → products was determined by measuring CH-radical concentration profiles in shock-heated 100-150 ppm ethane/1000 ppm O2 mixtures in Ar using cw, narrow-linewidth laser absorption at 431.131 nm. Comparing the measured CH concentration profiles to ones calculated using a detailed kinetics model, yielded the following average value for the rate coefficient independent of temperature over the range 2200-2600 K:\documentclass{article}\pagestyle{empty}\begin{document}$$ k_{\rm{CH}+\rm{O}_{2}} = 10^{(13.99 \pm 0.12)} \hbox{ cm}^{3} \hbox{ mol}^{-1} \hbox{ s}^{-1} $$\end{document}The experimental conditions were chosen such that the calculated profiles were sensitive mainly to the reactions CH+O2 → products and CH3+M → CH+H2+M. For the methyl decomposition reaction channel, the following rate-coefficient expression provided the best fit of the measured CH profiles:\documentclass{article}\pagestyle{empty}\begin{document}$$ k_{\rm{CH}_{3}+\rm{M}\rightarrow \rm{CH}+\rm{H}_{2}+\rm{M}} = 10^{(16.00 \pm 0.12)} \hbox{ exp($-$42900 K/\it T \rm) cm}^{3} \hbox{ mol}^{-1} \hbox{ s}^{-1} $$\end{document}Additionally, the rate coefficient of the reaction CH2+H→CH+ H2 was determined indirectly in the same system:\documentclass{article}\pagestyle{empty}\begin{document}$$ k_{\rm{CH}_{2}+\rm{H}} = 10^{14.15(+0.2,-0.6)} \hbox{ cm}^{3} \hbox{ mol}^{-1} \hbox{ s}^{-1} $$\end{document}© 1997 John Wiley & Sons, Inc.

Notes: Two analytical models are presented to approximate the temperature dependent, rotationally-averaged vibrational-state-specific dissociation rate coefficient for collisions between diatomic molecules and rare gas atoms at combustion temperatures. The new models are derived by making simplifying approximations to a more detailed theoretical model recently reported in the literature. For accuracy, the first model requires, for a given collision pair, knowledge of the maximum vibrational quantum number, a single vibrational-rotational energy and an interaction parameter for dissociation, all of which are tabulated in this article for collisions of Ar with p-H2, O2, N2, and CO. This is in contrast to the recently reported theoretical model, which requires knowledge of all vibrational-rotational energies below the dissociation threshold, in addition to the interaction parameter for dissociation. The second model is simpler and more general than the first, but less accurate. To completely specify this model, knowledge of only the hard sphere cross section, and the characteristic temperatures for vibration and dissociation is required. The two analytical models are shown to agree well with the published theoretical values, with the accuracy of each model increasing with increasing temperature. The present models provide an accurate and efficient means of computing thousands or millions of rate coefficients for use in numerical simulations of combustion processes that couple kinetic equations with the governing equations of fluid dynamics. © 1997 John Wiley & Sons, Inc.

Notes: A reaction mechanism for the photooxidation of dimethyldisulfide (DMDS) in aqueous acetonitrile has been established by kinetic modeling the UV absorbance vs. time curves under continuous irradiation. The model, built according to the known solution reactivity of oxysulfur radicals [1], consists of 22 steps involving 6 radical and 10 nonradical species. The first steps of the mechanism are the homolytic cleavage of the DMDS S - S bond with formation of methanethiyl radicals (CH3S·) followed by addition of these radicals to molecular oxygen. There are photoequilibria between thiyl (CH3S·), sulfinyl (CH3S·), and sulfonyl (CH3SO2·) radicals and the corresponding molecular species (methyl methanethiosulfinate CH3S(O)SCH3 or MMTSI, methyl methanethiosulfonate CH3S(O)2SCH3 or MMTS and meth-anesulfinic acid CH3S(O)OH or MSIA) which appear as long lived intermediates. Reactions of sulfonyl radicals with oxygen lead to methanesulfonic acid (CH3S(O)2OH) or MSA. Cleavage of sulfonyl radicals gives SO2 and CH3·, the parent compounds of sulfuric (H2SO4) and methanoic (HCOOH) acids. The predictive power of the model was tested at higher initial concentration of DMDS in anhydrous and aqueous acetonitrile. In these conditions, the proposed mechanism gives a semiquantitative description of the course of the reaction and reproduces the kinetic behavior of the long lived intermediates. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 825-834, 1997

Notes: The reaction \documentclass{article}\pagestyle{empty}\begin{document}$\rm {H + HI}\mathop\rightarrow\limits ^{1}\rm {H}_{2}+\rm {I}$\end{document} was studied at 298 K and millitorr pressures employing the “Very Low Pressure Reactor” (VLPR) kinetic technique. H-atoms were generated by dissociating H2 molecules (of a H2/Ar mixture) in a microwave discharge cavity that preceded the very low pressure well-mixed reaction vessel. Quadrupole mass spectrometry was used to analyze molecules and atoms. The mass signal intensities of I and HI were measured at both 20 and 40 eV ionizing potentials while those of H and H2 were measured at 40 eV due to the very weak signal of these species at lower ionization potentials. Three different exit flow orifices were utilized in the reported VLPR experiments of about 2, 3, and 5 mm inner diameter to vary the species concentration under steady-state reaction conditions. A rate constant of k1=(2.1±0.2)×10-11 cm3/molecule.s was determined for the forward reaction at 298 K, which lies between the two previously reported values directly measured at 298 K. Satisfactory mass balance relations were obtained for the iodine atoms (from the HI and I species) which were better than 90% for most of the experiments. The value of the reported rate constant (k1) is 14.3% higher than the value measured by Umemoto et al. [6], and 33.3% lower than the value measured by Lorenz et al. [4]. Based on this comparison, the activation energy E1 of the forward reaction probably lies between those two previously reported values of 580 and 720 cal/mol. Transition State Calculations of A1 and A2 for the reaction of \documentclass{article}\pagestyle{empty}\begin{document}$\rm {H + I}_{2}\mathop\rightarrow\limits ^{2}\rm {HI + I}$\end{document} are in good agreement with the data on both reactions and suggest an activation energy of about 500±100 cal/mol for E2.© 1997 John Wiley & Sons, Inc. Int J Chem Kinet: 29: 915-925, 1997.

Notes: Computer calculations of the kinetics of the ferric ion catalyzed decomposition of H2O2 by Walling and Weil are not in contradiction to the “complex mechanism.” The examination of their results reveals that their simulations correspond to the terminal state of the system in which the secondary complex between Fe3+ and H2O2 becomes stabilized.

Notes: The unimolecular decomposition of chemically activated methylallylether (MAE) formed by the cross combination of methoxymethyl and vinyl radicals was studied in the gas phase. The experimentally determined rate constant was found to be 1.11 × 108 sec-1 at 9.6°C for the decomposition of MAE into propene and formaldehyde. The decomposition of MAE via the six-center retro-“ene” type transition state is analyzed by using the RRKM unimolecular reaction theory. For the molecular parameter assignments of energized MAE, a model which contains one internal rotational mode is supported, and MAE decomposition is characterized by a tight complex model. The best agreement between experimental and theoretical results was found when a critical energy of 40.1 kcal/mol was used.

Notes: The reaction H + CH3OOH was investigated under conditions of excess atomic hydrogen concentration using a flow reactor attached to a photoionization mass spectrometer. The rate coefficient of the reaction was determined as \documentclass{article}\pagestyle{empty}\begin{document}$$ k = (2.8 \pm 0.9) \times 10^{- 13} {\rm exp\,}[- (1860 \pm 190){\rm cal}/RT \cdot {\rm mol\,}]\,{\rm cm}^3 /{\rm molec} \cdot {\rm sec} $$\end{document} The three important reaction channels were found to be with the individual contributions determined as indicated. The product methoxy and methylperoxy radicals react mainly with atomic hydrogen under the employed experimental conditions according to where the estimates for the percentage contributions of the various channels were derived from the measured product yields.

Notes: The application of modern theories of energy transfer to unimolecular reactions taking place at very high temperatures is discussed. It is shown that the efficiency of energy transfer for both reactant-reactant and reactant-inert diluent collisions may be substantially smaller than the values determined experimentally at lower temperatures. Consequently at high temperatures unimolecular falloff effects, particularly in some shock-tube measurements, may be greater than has been believed hitherto.The application of these calculations to the unimolecular reactions of cyclopropane, cyclobutane, and cyclohexene at temperatures around 1300°K is discussed, and it is shown that under shock-tube conditions the apparent first-order rate coefficient may be at least ten times less than the high-pressure limiting value.

Notes: The kinetics of the gamma radiation induced free radical chain decomposition of BrCH2CN in liquid cyclohexane (RH) was investigated over the temperature range of 60-170°C. In addition competitive experiments in the presence of CCl4 were carried out between 80 and 180°C. For the reactions the following Arrhenius expressions were derived: \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{l} {\rm log}k_3 /(2k_4)^{1/2} ({\rm l}^{{\rm 1/2}} /({\rm mol} \cdot {\rm sec})^{1/2}) = 4.07 \pm 0.35 - (11.96 \pm 0.63)/\theta \\ {\rm log}k_2 /k_5 = - 0.699 \pm 0.167) + (2.69 \pm 0.31)/\theta \\ \end{array} $$\end{document} where θ = 2.303RT in kcal/mol.The effect of CN substitution on the activation energies of reactions (2) and (3) was evaluated based on the present and previously published results. The CN group effect on halogen atom abstraction [reaction (2)] is discussed in terms of inductive and enthalpic factors.The differences E3 - E(CH3 + RH) and E(CCl2CN + RH) - E(CCl3 + RH), which yield a value of about 5.5 kcal/mol, are considered to reflect the cyano stabilization effect at the radical center confirming D(CH2(CN)-H) ∼ 93 kcal/mol.

Notes: Nanosecond flash photolysis of 1,2- and 1,8-dinitronaphthalenes (1,2-DNO2N; 1,8-DNO2N) in nonpolar and polar solvents shows transient species with absorption maxima and lifetimes dependent on solvent polarity. In deaerated n-hexane the absorption maxima and lifetimes (1/K) are 490 nm and 1.0 μsec for 1,2-DNO2N and 550 nm and 2.5 μsec for 1,8-DNO2N. In deaerated ethanol the corresponding values are 550 nm and 4.3 μsec for 1,2-DNO2N and 590 nm and 5.3 μsec for 1,8-DNO2N. The transient absorptions are attributed to the lowest triplet excited states T1 of the 1,2- and 1,8-DNO2N. The observed red shifts in the absorption maxima of the T1 states are indicative of the extent to which electronic charge is transferred intramolecularly during the T1 → Tn transitions. Furthermore, the increased lifetime of the T1 states with increasing solvent polarity indicates the intramolecular charge transfer character of the T1 states. Changes of dipole moments accompanying the T1 → Tn transitions as well as rate constants for electron or proton transfer and hydrogen abstraction reactions involving the T1 states of 1,2- and 1,8-DNO2N and tributyl tin hydride (Bu3SnH) as the hydrogen donor were determined together with the activation energy of the hydrogen abstraction reaction for the case of 1,2-DNO2N. The spectroscopic and kinetic data obtained in this work demonstrate that the triplet states of 1,2- and 1,8-DNO2N behave like n → π* states in nonpolar media while in polar solvents the n → π* character of these states is reduced with a simultaneous increase in their intramolecular charge transfer character.

Notes: Using the technique of molecular modulation spectrometry, we have measured directly the rate constants of several reactions involved in the oxidation of methyl radicals at room temperature: k1 is in the fall-off pressure regime at our experimental pressures (20-760 torr) where the order lies between second and third and we obtain an estimate for the second-orderlimit of (1.2 ± 0.6) × 10-12 cm3/molec · sec, together with third-order rate constants of (3.1 ± 0.8) × 10-31 cm6/molec2 · sec with N2 as third body and (1.5 ± 0.8) × 10-30 with neopentane; we cannot differentiate between k2a and k2c and we conclude k2a + (k2c) = (3.05 ± 0.8) × 10-13 cm3/molec · sec and k2b = (1.6 ± 0.4) × 10-13 cm3/molec · sec; k3 = (6.0 ± 1.0) × 10-11 cm3/molec · sec.

Notes: The reactions between SO2 and O2 were carried out in the presence of TiO2 and NiO under various partial pressures of SO2 and O2 at temperatures from 240 to 330°C. TiO2 and NiO were pretreated by applying an annealing effect from which the catalysts would have the different activity. The rates are the highest for TiO2 pretreated at high temperature in the region of 400 to 600deg;C in vacuum, 1.21 × 10-4 mmHg. In contrast, the rates are the lowest for NiO pretreated at high temperaturefrom 350 to 550°C. The data have been correlated with 1.4 and first-order kinetics for TiO2 and NiO, respectively. A reaction mechanism to explain the data was suggested.The quantities of anionic vacancies in TiO2 surfaces and of positive holes in NiO appeared to be paramount in determining the type of kinetics.

Notes: The general problem of eliciting reliable rate constants from experimental data is considered in detail for consecutive reactions. Practical aspects are emphasized.

Notes: The room temperature photolysis of 1,1-dichloroethane at 147 nm in the pressure range of 1.34-196.2 torr is characterized almost entirely by the molecular elimination of HCl, Cl2, and small quantities of H2. Acetylene is also produced. While it is possible that the C2H2 arises, in part, from the decomposition of vibrationally excited ground states of C2H3Cl and/or C2H4, in this particlar case serious consideration has to be given to alternative explanations where the products of the primary processes are formed in electronically excited states. The ±, elimination of molecular chlorine is not inconsistent with an increased degree of Cl—Cl interaction predicted for a «Rydberg «state of 1,1-C2H4Cl2. Varying small yields of CH4 are observed in the presence and absence of NO. The effect of large pressures of CF4 on the quantum yields of the major products is extremely small. The extinction coefficient for 1,1-C2H4Cl2 at 147 nm and 296°K is 246 ± 29 cm-1 ± atm-1.

Notes: NO Abstract.

Notes: 1,2-Fluorochloroethane was photolyzed at 147 nm in the pressure range of 3.8-20.9 torr. The effects of added NO, H2S, and large pressures of CF4 were also investigated. The exponential extinction coefficient at 147 nm and 296°K was found to be 147 ± 4 atm-1 · cm-1.The photochemistry in some respects is similar to that of ethyl chloride. The primary processes again appear to involve at least two excited states. One of these yields ethylene by FCl elimination (Φ ≃ 0.3) and has a lifetime of ∼3.2 × 10-10 sec, with respect to an internal conversion to the vibrationally excited ground state or, more probably, a collisionally induced crossover to a state decomposing mainly by carbon—halogen bond fission. The molecular elimination of HCl, H2, and small amounts of HF also occurs but not apparently from the same state as does FCl. The quantum yields of products with radical precursors, however, are not large, and hence little, if any, of the FCl and probably none of HCl, H2, and HF subsequently dissociates. The vinyl fluoride and vinyl chloride, accompanying the elimination of HF and HCl, are postulated as possible sources of the secondary production of acetylene.

Notes: Electron pulse radiolysis at ⋍298°K of 2 atm H2 containing 5 torr O2 produces HO2 free radical whose disappearance by reaction (1), HO2 + HO2 →H2O2 + O2, is monitored by kinetic spectrophotometry at 230.5 nm. Using a literature value for the HO2 absorption cross section, the values k1 = 2.5×10-12 cm3/molec·sec, which is in reasonable agreement with two earlier studies, and G(H) G(HO2) ⋍13 are obtained. In the presence of small amounts of added H2O or NH3, the observed second-order decay rate of the HO2 signal is found to increase by up to a factor of ⋍2.5. A proposed kinetic model quantitatively explains these data in terms of the formation of previously unpostulated 1:1 complexes, HO2 + H2O ⇋ HO2·H2O (4a) and HO2 + NH3⇋ HO2·NH3 (4b), which are more reactive than uncomplexed HO2 toward a second uncomplexed HO2 radical. The following equilibrium constants, which agree with independent theoretical calculations on these complexes, are derived from the data: 2×10-20≲K4a≲6.3 × 10-19 cm3/molec at 295°K and K4b = 3.4 × 10-18 cm3/molec at 298°K. Several deuterium isotope effects are also reported, including kH/kD = 2.8 for reaction (1). The atmospheric significance of these results is pointed out.

Notes: Rate constants have been estimated as a function of temperature for seven reactions of the type W + XYZ = WX + YZ, where W, X, Y, and Z are H and O atoms. From transition state theory and estimates of the heat capacities of activation, \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm int\, k/[cm}^{\rm 3} {\rm (mol} \cdot {\rm sec)] = 10}^{{\rm 15}{\rm .87}} \exp (\Delta S_{298}^{\circ _ \ne} /R)T^{0.75} \exp [- (\Delta H_{298}^{\circ _ \ne} + 0.74)/RT] $$\end{document} where int k is the rate constant per transferable atom for the forward and reverse reactions in the exothermic direction, and where ΔH°≠298 is in kcal/mol. Values of ΔS°≠298 and ΔH°≠298 were obtained from the above equation and previously measured and evaluated rate constants at 298°K. The results are summarized in a table. Rate constants were calculated at temperature from 250 to 2000 K. The estimated rate constants were compared with recommended values. The results for ΔH°≠298 for reactions (15), (16), (17), and (19), in which a stable intermediate may precede the transition state, together with similar results previously found for reactions X + YZ = XY + Z, suggests that many such reactions may have values of ΔH°≠298 that are close to zero. The result for the reaction O + O3 = O2 + O2 is however, an exception to the foregoing perhaps because it is the reaction of a singlet with a triplet.ΔS°≠298 for the same reaction is unexpectedly low.

Notes: Mixtures of N2O, H2, O2, and trace amounts of NO and NO2 were photolyzed at 213.9 nm, at 245°-328°K, and at about 1 atm total pressure (mostly H2). HO2 radicals are produced from the photolysis and they react as follows:Reaction (1b) is unimportant under all of our reaction conditions. Reaction (1a) was studied in competition with reaction (3) from which it was found that k1a/k31/2 = 6.4 × 10-6 exp { z-(1400 ± 500)/RT} cm3/2/sec1/2. If k3 is taken to be 3.3 × 10-12 cm3/sec independent of temperature, k1a = 1.2 × 10-11 exp {-(1400 ± 500)/RT} cm3/sec. Reaction (2a) is negligible compared to reaction (2b) under all of our reaction conditions. The ratio k2b/k1 = 0.61 ± 0.15 at 245°K. Using the Arrhenius expression for k1a given above leads to k2b = 4.2 × 10-13 cm3/sec, which is assumed to be independent of temperature. The intermediate HO2NO2 is unstable and induces the dark oxidation of NO through reaction (-2b), which was found to have a rate coefficient k-2b = 6 × 1017 exp {-26,000/RT} sec-1 based on the value of k1a given above. The intermediate can also decompose via Reaction (10b) is at least partially heterogeneous.

Notes: Tertiary-amyl amine has been decomposed in single-pulse shock-tube experiments. Rate expressions for several of the important primary steps are \documentclass{article}\pagestyle{empty}\begin{document}$$ k(t{\rm C}_5 {\rm H}_{11 - {\rm NH}_2} \to t{\rm C}_5 {\rm H}_{11}\!\!\cdot + {\rm NH}_2\cdot) = 10^{15.9} \exp (-39,700/T)\sec ^{- 1} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k({\rm C}_2 {\rm H}_5- {\rm C}({\rm CH}_3)_2{\rm NH}_2 \to {\rm C}_2 {\rm H}_5 \cdot + \cdot{\rm C}({\rm CH}_3)_2{\rm NH}_2) = 10^{16.5} \exp (- 38,500/T)\sec ^{- 1} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k(t{\rm C}_5 {\rm H}_{11} {\rm NH}_2 \to {\rm C}_5 {\rm H}_{10} + {\rm NH}_3) 〈10^{14.5} \exp (- 37,200/T)\sec ^{- 1} $$\end{document}This leads to D(CH3—H) - D(NH2—H) = -10.5 kJ and D[(CH3)3C—H] - D[(CH3)2NH2C—H] = + 6 kJ.The present and earlier comparative rate single-pulse shock-tube data when combined with high-pressure hydrazine decomposition results-(after correcting for fall off effects through RRKM calculations) gives \documentclass{article}\pagestyle{empty}\begin{document}$$ [k_r^2 (t{\rm C}_5 {\rm H}_{11} \cdot,{\rm NH}_2 \cdot)/k_r (t{\rm C}_5 {\rm H}_{11} \cdot,t{\rm C}_5 {\rm H}_{11} \cdot)k_r ({\rm NH}_2 \cdot,{\rm NH}_2 \cdot)]^{1/2} \sim 2\,{\rm at}\,1100^o {\rm K} $$\end{document} where kr(…) is the recombination rate involving the appropriate radicals. This suggests that in this context amino radical behavior is analogous to that of alkyl radicals. If this agreement is exact, then \documentclass{article}\pagestyle{empty}\begin{document}$$ k_\infty ({\rm N}_2 {\rm H}_4 \to 2{\rm NH}_2 \cdot) = 10^{16.25} \exp (- 32,300/T)\sec ^{- 1} $$\end{document} Rate expressions for the primary step in the decomposition of a variety of primary amines have been computed. In the case of benzyl amine where data exist the agreement is satisfactory. The following differences in bond energies have been estimated: \documentclass{article}\pagestyle{empty}\begin{document}$$ D(i{\rm C}_3 {\rm H}_7 {-\!-} {\rm H}) {-\!-} D[{\rm CH}_3 ({\rm NH}_2){\rm CH} {-\!-} {\rm H}] = 14.3\,{\rm kJ} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ D({\rm C}_2 {\rm H}_5 {-\!-} {\rm H}) - D({\rm NH}_2 {\rm CH}_2 {-\!-} {\rm H}) = 15.9\,{\rm kJ} $$\end{document}

Notes: The thermal decomposition of F5SOOSF5, P, in the presence of CO has been investigated between 130.1° and 161.9°C at total pressures between 50 and 600 torr. The reaction is homogeneous, and the only final products formed are CO2 and S2F10. The rate of reaction is proportional to the pressure of P. The partial pressures of CO and O2 and the total pressure have no influence on the course of reaction: \documentclass{article}\pagestyle{empty}\begin{document}$$ - \frac{{d\left[P \right]}}{{dt}} = k\left[P \right] $$\end{document}The results are explained by the following mechanism:

Notes: The unimolecularity of the thermal dehydrogenation of cyclopentene has been confirmed using the technique of very low-pressure pyrolysis (VLPP). Application of RRKM theory shows that the experimental unimolecular rate constants obtained over the temperature range of 942°-1152°K are consistent with the high-pressure Arrhenius parameters given by\documentclass{article}\pagestyle{empty}\begin{document}$$ \log (k/\sec ^{-1}) = 13.35 - 61/\theta $$\end{document} where θ = 2.303 RT kcal/mol. These parameters are in good agreement with static and shock tube studies. No firm evidence could be found for any side reactions or reversibility under the experimental conditions used.

Notes: The thermal decomposition of isopropyl peroxide in solvents is shownto be a competition between unimolecular homolysis (kr) and an electrocyclic reaction yielding H2 plus acetone (kH). The value of kH increases markedly with increasing solvent polarity: PhCH3 〈 i-PrOH 〈 MeOH 〈 H2O. Log kH correlates linearly with Et (or Z). The effect on kr is similar but less pronounced. Log kr's for both i-Pr2O2 and t-Bu2O2 are shown to correlate with the molar solubility parameter δ. The negligible contribution of the electrocyclic reaction to thermal decompositions of peroxides in the vapor phase is thus not due to peculiar behavior of that reaction, which clearly has a polartransition state. It is argued that the transition state for unimolecular homolysis has no polar character despite the apparent sensitivity of homolysis rates to solvent polarity.

Notes: The kinetics of the gas-phase decomposition of 1-methylcyclohex-1-ene has been studied over the temperature range of 1000°-1180° K in a single-pulse shock tube using a comparative-rate technique. The retro Diels-Alder reaction to ethylene and isoprene accounts for the bulk of the products with a rate constant given by \documentclass{article}\pagestyle{empty}\begin{document}$$ k = 10^{15.57} \exp \left({- 35,000/T} \right)\sec ^{- 1} $$\end{document}

Notes: The decomposition of acetonyl bromide, isopropenylmethylether, and hexanedione-2,5 was studied using the very-low-pressure pyrolysis (VLPP) technique. The acetonyl radical is a product of each reaction. Arrhenius parameters determined are or acetonyl bromide ← acetonyl + Br: \documentclass{article}\pagestyle{empty}\begin{document}$$ \log k\left({\sec ^{- 1}} \right) = 16.0 - 62.5/\theta\,{\rm at}\,300^{\rm o} {\rm K} $$\end{document} and for isopropenylmethylether ← acetonyl + CH3: \documentclass{article}\pagestyle{empty}\begin{document}$$ \log k\left({\sec ^{- 1}} \right) = 15.8 - 66.3/\theta\,{\rm at}\,300^{\rm o} {\rm K} $$\end{document} These lead to values of acetonyl stabilization energy (SE) of 0.8 and -4.0 kcal/mol, respectively. Comparison of the pyrolyses of hexanedione-2,5 and 2,5-dimethylhexane indicate a value of SE ∼ 2 kcal/mol. The total of these results is taken, along with previous work, to indicate that 0 ≲ SE ≲ 2 kcal/mol.