The Spin‐Forbidden Reaction of Ground‐State Sulfur Atoms with Ethylene

Ground‐state S‐atoms (³P_J) were generated by pulsed laser photolysis of carbonyl sulfide (OCS) precursor and monitored by time‐resolved resonance fluorescence. The kinetics were studied over the temperature range of 291–1052 K. Below 900 K, the effective bimolecular rate constant k₁ was found to be independent of pressure and also to be in good accord with prior measurements made at 442 K and below. At higher temperatures, fall‐off curves were characterized. These demonstrate that the reaction is dominated by addition. The high‐pressure limit is summarized as k_∞ = 1.5 × 10^?11 exp(?8.4 kJ mol^?1/RT) cm³ molecule^?1 s^?1. The low‐pressure limiting rate constant is also obtained. The observation of formation of one or more adducts even at ～1000 K constrains their thermochemistry, and comparison with the computed reaction enthalpies for various candidates in the literature shows the addition products can only be accessed via intersystem crossing. Estimated Rice–Ramsperger–Kassel–Marcus (RRKM) addition rate constants at the low‐pressure limit for formation of vinylthiol and ethanethial are in accord with the observed kinetics assuming that the collisional efficiency near 1000 K is about 0.1.     

Abstraction of hydrogen by methylene

The photolysis of CD₂CO at 313 nm in the presence of neopentane was carried out over the temperature range 576–706 K. Analysis of the products and isotopic analysis of the methanes demonstrate abstraction of H from neopentane and D from CD₂CO by methylene. The relative kinetics of abstraction of H and D have been measured over the temperature range, and the absolute value for the collision yield of the abstraction of H from neopentane by CD₂ at 653 K has been been estimated to be about 1.5 × 10¹¹ mole^?1 cm³ sec^?1, a value 10³ times larger than the corresponding reaction of CH₃.     

Kinetics of OH radical reaction with phenanthrene: New absolute rate measurements and comparison with other PAHs

Using an in situ pulsed laser photolysis/pulsed laser‐induced fluorescence/technique, the OH reaction kinetics of a three‐ring polycyclic aromatic hydrocarbon (PAH), phenanthrene (and its deuterated form), was investigated over the temperature range of 373–1000 K. This study represents the first examination of the OH kinetics for phenanthrene at elevated temperatures using the absolute rate technique. The phenanthrene results indicate a temperature dependence similar to its isomer anthracene, reported previously in R. Ananthula, T. Yamada, and P. H. Taylor, J Phys Chem A 2006, 100, 3559–3566, over a similar temperature range. The phenanthrene rate constants are similar to anthracene at high temperature (ca. 1000 K) and a factor of ca. 2 lower at low temperatures (373–700 K). The rate measurements were best fitted by the following two‐parameter expression of the form ATⁿ: k₁(373–1000 K) = 4.98 ± 2.96 × 10^?6 * T^?1.97±0.10 (in units of cm³ molecule^?1 s^?1, error limits ±1σ). Rate measurements with deuterated phenanthrene below 725 K were indistinguishable from the phenanthrene rate measurements, within random error limits, providing strong evidence for an OH‐addition mechanism. The effects of PAH size on their reactivity with OH radicals based on selected data over the temperature range of 243–1200 K are discussed. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 629–637, 2007     

Rate of decomposition of hexafluoroazomethane and the absolute rate of recombination of trifluoromethyl radical at higher temperatures

The unimolecular homogeneous decomposition of hexafluoroazomethane was studied in a VLPP apparatus in the temperature range 720–1050 K and is consistent with the following Arrhenius parameters: at 900 K, where the A factor was assumed to be the same as for 2,2′-azoisobutane. The homogeneous rate of recombination of ·CF₃ radicals at temperatures around 1000 K was also studied under VLPP conditions and was found to be in the fall-off region, corresponding to k/k^∞ = 8.5 × 10^?3 when a rotational transition-state model was used. This model predicts an essentially constant value of k_r^∞ of 10^9.7 over the temperature range 300–1000 K.     

Concentration dependence of NaCl in a wide range of temperatures and pressures

We use our own and literature data on density, ultrasound propagation velocity, and isobaric heat capacity to study the concentration, temperature, and pressure dependences of solvation numbers in aqueous NaCl solutions. We show that, in the parameter range: m = 0–6.0 mol·kg^?1, p = 1–1000 bar, and T = 283.15–323.15 K, the solvation numbers decrease with increasing concentration, pressure, and temperature.     

Absolute reaction rate of chlorine atoms with neopentane

The reaction of atomic chlorine with neopentane was studied in the gas phase with the Very Low Pressure Reactor (VLPR) technique over the temperature range 273–333 K. The absolute reaction rate was found to be temperature-independent, and the average rate constant was k₁ = (1.11± 0.13) × 10^?10 cm³ molecule^?1 s^?1 within experimental error. The reaction proceeds via metathesis of a hydrogen atom with no activation energy, and leads to the formation of HCl and neopentyl radical. © 1995 John Wiley & Sons, Inc.     

Analysis of nitromethane thermal decomposition at low temperatures

The thermal decomposition of nitromethane (NM) over the temperature range from 580 to 700 K at pressures of 4 Torr to 40 atm was analyzed. On the basis of literature data, with the use of theoretical transitional curves of the modified Kassel integral, the rate constants k of NM decomposition at the upper pressure limit were determined. The values thus obtained are in good agreement with the results of extrapolation of the high-temperature (1000–1400 K) k _{1, ∞} values to lower temperatures. The reasons for which the NM decomposition rate constants differ by two orders of magnitude at low temperatures are considered. A general expression for the NM decomposition rate constant at the upper pressure limit over the 580–1400 K temperature range was determined: k _{1, ∞} = (1.8 ± 0.7) × 10¹⁶ exp((?58.5 ± 2)/R _T ) s^?1. These data disprove the hypothesis that a nitro-nitrite rearrangement takes place during the NM decomposition at low temperatures.     

Modelling of the homogeneously catalyzed and uncatalyzed pyrolysis of neopentane: Thermochemistry of the neopentyl radical

The mechanism for neopentane (NpH) pyrolysis in the absence and presence of additives isobutene, HCl and HBr, in the temperature range 750–800 K, has been reinvestigated with the aid of computer simulation and sensitivity analysis techniques. With best values assigned to all rate constants in the kinetic chain, a basic mechanism comprising 18 reversible reactions involving 19 atomic, radical, and molecular species has been used to simulate pure neopentane pyrolysis data. Predictions of major and minor product yields provided quantitative agreement with experimental data against which the model was tested. The mechanism was supplemented by additional species and reactions in order to simulate experimental neopentane pyrolysis data in the presence of HCl and HBr additives. An apparent discrepancy between a recent direct measurement of k₅, the rate constant for thermal decomposition of the neopentyl radical [1], and that reported from studies of neopentane pyrolysis in the presence and absence of HCl [2], has been identified as being due to the use of an incomplete mechanism in the latter determination. Simulations of hydrogen halide catalyzed pyrolyses exhibit a high sensitivity to the thermochemical parameters associated with the neopentyl radical (Np). The influence of uncertainties in ΔH(Np) and S(Np) are evaluated and lead to suggested values ΔH(Np) = 8.7 ± 0.8 kcal mol^?1 and S(Np) = 78.8 ± 1.0 cal mol^?1 K^?1. © 1993 John Wiley & Sons, Inc.     

Shock tube pyrolysis of pyrrole and kinetic modeling

The kinetics of pyrolysis of pyrrole dilute in argon have been studied in a single pulse shock tube, using capillary column GC, together with GC/MS and FTIR for product identification, over the temperature range 1200–1700 K, total pressures of 7.5–13.5 atm and nominal mixture compositions of pyrrole of 5000 and 700 ppm (nominal concentrations of 5 × 10^?7 and 7 × 10^?8 mol cm^?3). Time-resolved measurements of the rate of disappearance of pyrrole behind reflected shock waves have been made by absorption spectroscopy at 230 nm, corresponding to the lowest ¹π* ← ¹π transition of pyrrole at pressures of 20 atm and mixture compositions between 1000–2000 ppm pyrrole (1.7–3.0 × 10^?7 mol cm^?3) over the temperature range of 1300 to 1700 K. At the lower end of the studied temperature range, the isomers of pyrrole, allyl cyanide and cis- and trans-crotononitrile, were the principal products, together with hydrogen cyanide and propyne/allene. At elevated temperatures, acetylene, acetonitrile, cyanoacetylene, and hydrogen became important products. The rate of overall disappearance of pyrrole, as measured by absorption spectrometry, was found to be first order in pyrrole concentration, with a rate constant k_dis(pyrrole) = 10^14.1±0.7 exp(?74.1 ± 3.0 kcal mol^?1/RT) s^?1 between 1350–1600 K and at a pressure of 20 atm. First order dependence of pyrrole decomposition and major product formation was also observed in the single pulse experiments over the range of mixture compositions studied. A 75-step reaction model is presented and shown to substantially fit the observed temperature profiles of the major product species and the reactant profile. In the model the initiation reaction is postulated to be the reversible formation of pyrrolenine, (2H-pyrrole). Pyrrolenine can undergo ring scission at the C2? N bond forming a biradical which can rearrange to form allyl cyanide and crotononitrile or undergo decomposition to form HCN and C₃H₄ or acetylene and a precursor of acetonitrile. The model predicts an overall rate of disappearance of pyrrole in agreement with the experimental measurements.     

Self-inhibition or the lack of it in the pyrolyses of neopentane and n-hexane

Published data show that in its early stages (up to 3% decomposition), the pyrolysis of n-hexane in the ranges 723–823 K and 10–100 Torr is not inhibited by the olefin products, in contrast with neopentane pyrolysis which is very strongly inhibited in similar conditions. Detailed consideration of the chain mechanisms for the two pyrolyses shows that the reactivity of the chain terminating radical towards hydrogen abstraction from an allylic C? H bond in product olefin is the factor which determines whether or not observable self-inhibition occurs. Thus, n-hexane pyrolysis, whose chain decomposition is terminated by recombination and disproportionation of ethyl, is not significantly self-inhibited, whereas that of neopentane which is terminated by recombination of methyl is very strongly inhibited because methyl is 14× more reactive than ethyl. The implications for other alkanes are briefly discussed.     

Decane oxidation in a shock tube

The ignition delay of n‐decane and oxygen diluted in argon was investigated for a series of mixtures ranging from 0.49 to 1.5% decane and 4.16 to 23.25% O₂ diluted in argon. The temperature range was 1239–1616 K and the pressure range was 1.82–10.0 atm. All experiments were performed in a heated shock‐tube. An overall ignition delay equation was deduced for 144 experiments: τ = 10⁻¹² exp(+34240/RT)[C₁₀H₂₂]^0.60[O₂]^−1.305[Ar]^0.08 s. Product distribution from preignition periods were measured. Detailed simulation schemes available in the literature were checked and a corrected model is proposed that fits well our experiments. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 703–713, 2006     

The H+NO recombination reaction over a wide temperature range

Rate coefficients of the title reaction have been measured in a high‐temperature photochemistry (HTP) reactor using Ar as the bath gas. H atoms were generated by flash photolysis of NH₃ and their relative concentrations were monitored by resonance fluorescence. The data are best fitted by k(295–905 K) = 6.5 × 10^?34 (T/K)^0.206 exp(780K T) cm⁶ molecule^?2 s^?1, with ±2σ precision values varying from 16 to 36% and corresponding suggested accuracy levels of 29–42%. Using a literature value for the relative collision efficiencies of N₂ and Ar indicates that for N₂ as the third body the above rate coefficient expression should be multiplied by 1.6. This leads to good agreement with two recent near 1000 K measurements. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 374–380, 2003     

The thermodynamic properties of polytetrafluoroethylene

Polytetrafluoroethylenes of different crystallinity were analyzed between 220 and 700 K by differential scanning calorimetry. A new computer coupling of the standard DSC is described. The measured heat capacity data were combined with all literature data into a recommended set of thermodynamic properties for the crystalline polymer and a preliminary set for the amorphous polymer (heat capacity, enthalpy, entropy, and Gibbs energy; range 0–700 K). The crystal heat capacities have been linked to the vibrational spectrum with a θ₃ of 54 K, and θ₁ of 250 K, and a full set of group vibrations. C_v to C_p conversion was possible with a Nernst–Lindemann constant of A = 1.6 × 10^?3 mol K/J. The glass transition was identified as a broad transition between 160 and 240 K with a ΔC_p of 9.4 J/K mol. The room-temperature transitions at 292 and 303 K have a combined heat of transition of 850 J/mol and an entropy of transition of 2.90 J/K mol. The equilibrium melting temperature is 605 K with transition enthalpy and entropy of 4.10 kj/mol and 6.78 J/K mol, respectively. The high-temperature crystal from is shown to be a condis crystal (conformationally disordered), and for the samples discussed, the crystallinity model holds.     

Very-low-pressure pyrolysis (VLPP) of group IV (A) tetramethyls: Neopentane and tetramethyltin

The decomposition of neopentane was studied using the very-low-pressure pyrolysis (VLPP) technique at temperatures from 1000 to 1260 K. The derived Arrhenius parameters are consistent with δH_f⁰(t-butyl) = 8.4 kcal/mol. Using the above A factor, data on the decomposition of tetramethyltin yield DH⁰(Sn(CH₃)₃ - CH₃) = 69 ± 2 kcal/mol.     

Kinetics of the gas phase reaction of Cl atoms with a series of organics at 296 ± 2 K and atmospheric pressure

Using a relative rate technique, rate constants have been determined for the gas phase reactions of Cl atoms with a series of organics at 296 ± 2 K and atmospheric pressure of air. Using a rate constant of 1.97 × 10^?10 cm³ molecule^?1 s^?1 for the reaction of Cl atoms with n-butane, the following rate constants (in units of 10^?11 cm³ molecule^?1 s^?1) were obtained: ethane, 6.38 ± 0.18; propane, 13.4 ± 0.5; isobutane, 13.7 ± 0.2; n-pentane, 25.2 ± 1.2; isopentane, 20.3 ± 0.8; neopentane, 11.0 ± 0.3; n-hexane, 30.3 ± 0.6; cyclohexane, 31.1 ± 1.4; 2,3-dimethylbutane, 20.7 ± 0.6; n-heptane, 34.1 ± 1.2; acetylene, 6.28 ± 0.18; ethene, 10.6 ± 0.3; propene, 24.4 ± 0.8; benzene, 1.5 ± 0.9; and toluene, 5.89 ± 0.36. These data are compared and discussed with the available literature values.     

Vapor–liquid equilibria of 2-butanol + aromatic hydrocarbons at 308.15 k

Vapor–liquid equilibria (VLE) data of 2-butanol?+?benzene or toluene or o- or m- or p-xylene measured by static method at 308.15?±?0.01?K over the entire composition range are reported. The excess molar Gibbs free energies of mixing (G ^E) for these binary systems have been calculated from total vapor pressure data using Barker's method. The G ^E for these binary systems are also analyzed in terms of the Mecke–Kempter type of association model with a Flory contribution term using two interaction parameters and it has been found that this model describes well the G ^E values of binary systems benzene or toluene.     

Dependence of the pure quadrupole resonance frequency on temperature for KBrO3

The pure quadrupole resonance frequency of KBrO₃ in the temperature range 4.17–300.16 K was determined experimentally and compared with the model developed by Stahl which contains three adjustable constants. Excellent agreement between the experimental data and the model was obtained when considering only the temperature range 4.17–52 K. As a result of the comparison, the following values are suggested for KBrO₃: the resonance frequency at 0 K is 179.50373 MHz, the Debye temperature, Θ_d, is 108 K, and the rotational energy, Iω_l², of each of the first two modes of oscillation of the BrO₃ group is 1.707 × 10^?18 kg m². Here I is the moment of inertia and ω_l is the lattice vibration frequency. Comparison of model and experimental data over the entire temperature range from 4.17 to 300.16 K shows that the suggested theory reflects very well the general trend of the experimental data but lacks in some detail. Copyright © 2003 John Wiley & Sons, Ltd.     

Standard reactions for comparative rate studies: Experiments on the dehydrochlorination reactions of 2‐chloropropane,chlorocyclopentane, and chlorocyclohexane

Single pulse shock tube studies of the thermal dehydrochlorination reactions (chlorocyclopentane → cyclopentene + HCl) and (chlorocyclohexane → cyclohexene + HCl) at temperatures of 843–1021 K and pressures of 1.4–2.4 bar have been carried out using the comparative rate technique. Rate constants have been measured relative to (2‐chloropropane → propene + HCl) and the decyclization reactions of cyclohexene, 4‐methylcyclohexene, and 4‐vinylcyclohexene. Absolute rate constants have been derived using k(cyclohexene → ethene + butadiene) = 1.4 × 10¹⁵ exp(?33,500/T) s^?1. These data provide a self‐consistent temperature scale of use in the comparison of chemical systems studied with different temperature standards. A combined analysis of the present results with the literature data from lower temperature static studies leads to

• k(2‐chloropropane) = 10^{(13.98±0.08)} exp(?26, 225 ± 130) K/T) s^?1; 590–1020 K; 1–3 bar
• k(chlorocylopentane) = 10^{(13.65 ± 0.10)} exp(?24,570 ± 160) K/T) s^?1; 590–1020 K; 1–3 bar
• k(chlorocylohexane) = 10^{(14.33 ± 0.10)} exp(?25,950 ± 180) K/T) s^?1; 590–1020 K; 1–3 bar

Including systematic uncertainties, expanded standard uncertainties are estimated to be about 15% near 600 K rising to about 25% at 1000 K. At 2 bar and 1000 K, the reactions are only slightly under their high‐pressure limits, but falloff effects rapidly become significant at higher temperatures. On the basis of computational studies and Rice–Ramsperger–Kassel–Marcus (RRKM)/Master Equation modeling of these and reference dehydrochlorination reactions, reported in more detail in an accompanying article, the following high‐pressure limits have been derived:

• k_∞ (2‐chloropropane) = 5.74 × 10⁹T^1.37 exp(?25,680/T) s^?1; 600–1600 K
• k_∞ (chlorocylopentane) = 7.65 × 10⁷T^1.75 exp(?23,320/T) s^?1; 600–1600 K
• k_∞ (chlorocylohexane) = 8.25 × 10⁹T^1.34 exp(?25,010/T) s^?1; 600–1600 K

© 2011 Wiley Periodicals, Inc.

1 This article is a U.S. Government work and, as such, is in the public domain of the United States of America.

Int J Chem Kinet 44: 351–368, 2012     

Detailed kinetic modeling of 1,3‐butadiene oxidation at high temperatures

The high‐temperature kinetics of 1,3‐butadiene oxidation was examined with detailed kinetic modeling. To facilitate model validation, flow reactor experiments were carried out for 1,3‐butadiene pyrolysis and oxidation over the temperature range 1035–1185 K and at atmospheric pressure, extending similar experiments found in the literature to a wider range of equivalence ratio and temperature. The kinetic model was compiled on the basis of an extensive review of literature data and thermochemical considerations. The model was critically validated against a range of experimental data. It is shown that the kinetic model compiled in this study is capable of closely predicting a wide range of high‐temperature oxidation and combustion responses. Based on this model, three separate pathways were identified for 1,3‐butadiene oxidation, with the chemically activated reaction of H^· and 1,3‐butadiene to produce ethylene and the vinyl radical being the most important channel over all experimental conditions. The remaining uncertainty in the butadiene chemistry is also discussed. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 589–614, 2000     

Compressibility of Gas Hydrates

Experimental data on the pressure dependence of unit cell parameters for the gas hydrates of ethane (cubic structure I, pressure range 0–2 GPa), xenon (cubic structure I, pressure range 0–1.5 GPa) and the double hydrate of tetrahydrofuran+xenon (cubic structure II, pressure range 0–3 GPa) are presented. Approximation of the data using the cubic Birch–Murnaghan equation, P=1.5B₀[(V₀/V)^7/3?(V₀/V)^5/3], gave the following results: for ethane hydrate V₀=1781 ų, B₀=11.2 GPa; for xenon hydrate V₀=1726 ų, B₀=9.3 GPa; for the double hydrate of tetrahydrofuran+xenon V₀=5323 ų, B₀=8.8 GPa. In the last case, the approximation was performed within the pressure range 0–1.5 GPa; it is impossible to describe the results within a broader pressure range using the cubic Birch–Murnaghan equation. At the maximum pressure of the existence of the double hydrate of tetrahydrofuran+xenon (3.1 GPa), the unit cell volume was 86 % of the unit cell volume at zero pressure. Analysis of the experimental data obtained by us and data available from the literature showed that 1) the bulk modulus of gas hydrates with classical polyhedral structures, in most cases, are close to each other and 2) the bulk modulus is mainly determined by the elasticity of the hydrogen‐bonded water framework. Variable filling of the cavities with guest molecules also has a substantial effect on the bulk modulus. On the basis of the obtained results, we concluded that the bulk modulus of gas hydrates with classical polyhedral structures and existing at pressures up to 1.5 GPa was equal to (9±2) GPa. In cases when data on the equations of state for the hydrates were unavailable, the indicated values may be recommended as the most probable ones.