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  • Wiley-Blackwell  (14)
  • Nature Publishing Group  (1)
  • 1
    ISSN: 0538-8068
    Keywords: Chemistry ; Physics Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The absolute rate constants have been measured for several gas-phase chlorine atom-molecule reactions at 25°C by resonance fluorescence. These reactions and their corresponding rate constants in units of cm3 mole-1 sec-1 are: The effects of varying the substrate pressure, total pressure, light intensity and chlorine-atom source on the value of the bimolecular rate constants have been investigated for all these reactions. Conditions under which no competing side reaction occurs were established and the reported rate constants were measured under these conditions. For reactions (2), (5), (6), (7), and 8, there is a discrepancy of a factor of two between the rate constants measured in this work and values in the literature; it is suggested that this is due to an error in the previously measured value of kCH4/kH2 upon which the relative measurements in the literature ultimately depend.
    Additional Material: 5 Ill.
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  • 2
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Using the technique of flash photolysis-resonance fluorescence, absolute rate constants have been measured for the reaction of S(3P) with propene and 1-butene. Variations in experimental conditions included the following: temperature (215-500°K); total pressure a factor of 10; olefin concentration, a factor of 6; flash intensity (S atom concentration), a factor of 10. It was found that over these variations in the experimental conditions only the temperature had a measureable effect on the bimolecular rate constant. The derived Arrhenius rate expressions for the reactions (2) and (3) were as follows: \documentclass{article}\pagestyle{empty}\begin{document}$$ k_2 = \left( {6.03 \pm 0.72} \right) \times 10^{ - 12} \exp \left( {\frac{{ - 0.38 \pm 0.09kcal/mol}}{{RT}}} \right) $$\end{document} temperature range 214-500°K \documentclass{article}\pagestyle{empty}\begin{document}$$ k_3 = \left( {7.41 \pm 1.15} \right) \times 10^{ - 12} \exp \left( {\frac{{ - 0.36 \pm 0.09kcal/mol}}{{RT}}} \right) $$\end{document} Units are cm3 molec-1 s-1.
    Additional Material: 2 Ill.
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  • 3
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The flash photolysis-resonance fluorescence technique has been used to measure the reaction of ground-state sulfur atoms with molecular oxygen as a function of both temperature and total pressure. The most suitable source of S(3P) for this study was found to be COS in the presence of CO2, as a diluent gas and with the photolysis flash filtered so as to remove all radiation of wavelengths below 1650 Å. Under these conditions, it was found that over the temperature range of 252-423°K the rate data could be fit to a simple Arrhenius-type equation of the form \documentclass{article}\pagestyle{empty}\begin{document}$$k_1 = (2.24 \pm 0.27) \times 10^{ - 12} {\rm exp}\left({\frac{{{\rm - 0}{\rm .00} \pm {\rm 0}{\rm .10 kcal/mole}}}{{RT}}} \right)$$\end{document} Units are cm3 molec-1 s-1. The small A-factor for this reaction, the lack of any pressure dependence, and the direct observation of the production of O(3P) with increasing reaction time suggest that the S(3P) atom attacks the O2(3Σ) molecule end-on forming SOO which rapidly falls apart to form SO (3Σ) and O(3P).
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  • 4
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Absolute rate constants for the reaction of S(3P) with ethylene were measured over an ethylene concentration range of 7, a total pressure of 50 to 400 torr, and a flash intensity range of 10. At 298°K, the bimolecular rate constant was found to be invariant over this range of variables and had a measured value of 4.96 × 10-13 cm3 molec-1 s-1. Over the temperature range of 218° to 442°K, the rate data could be fit to a simple Arrhenius equation of the form \documentclass{article}\pagestyle{empty}\begin{document}$$k_1 = (7.13 \pm 0.74) \times 10^{ - 12} {\rm exp}\left({\frac{{{\rm - 1}{\rm .58} \pm {\rm 0}{\rm .08 kcal/mole}}}{{RT}}} \right)$$\end{document} Units are cm3 molec-1 s-1. The dependence of the measured value of k1 on the concentration of the reaction product ethylene episulfide is discussed.
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  • 5
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The third order rate coefficients for the addition reaction of Cl with NO2, Cl + NO2 + M → ClNO2 (ClONO) + M; k1, were measured to be k1(He) = (7.5 ± 1.1) × 10-31 cm6 molecule-2 s-1 and k1(N2) = (16.6 ± 3.0) × 10-31 cm6 molecule-2 s-1 at 298 K using the flash photolysis-resonance fluorescence method. The pressure range of the study was 15 to 500 torr He and 19 to 200 torr N2. The temperature dependence of the third order rate coefficients were also measured between 240 and 350 K. The 298 K results are compared with those from previous low pressure studies.
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  • 6
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Homogeneous films comprised of mixtures of polystyrene and poly(vinyl methyl ether) can be obtained by evaporation from a ternary solution containing toluene as the solvent. Heterogeneous films result when the solvent is trichloroethylene. The possibility that a heterogeneous film cast from trichloroethylene can be transformed to a homogeneous one by physical means is a logical expectation when the polymer-polymer interaction is favorable, though as yet no comprehensive report has appeared in the literature. We have accomplished the transformation by increasing the temperature. Optical microscopy and glass transition experiments were employed to observe the effects.
    Additional Material: 8 Ill.
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  • 7
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Rate parameters for the reaction of ground-state atomic sulfur, S(3P), with the olefins cis-2-butene and tetramethylethylene have been determined over a temperature range of ∽280°K. A major finding of this study was that the rate constants for both reactions showed negative temperature dependencies. When k is expressed in the form of an Arrhenius equation, this necessarily leads to negative activation energies: k1 = (4.68 ± 0.70) × 10-12 exp (+0.23 ± 0.09 kcal/mole)/RT (219°-500°K) k2 = (4.68 ± 1.70) × 10-12 exp (+1.29 ± 0.23 kcal/mole)/RT (252°-500°K) Units are cm3 molec-1s-1. When a threshold energy of 0.0 kcal/mole is assumed for reaction (2), the temperature dependence of the preexponential term has a value of T-2. Making the usual simplifying assumptions, neither collision theory nor transition state theory leads to a preexponential factor with a strong enough negative temperature dependence. A comparison of these results with those derived from studies of the reactions of atomic oxygen, O(3P), with the same olefins shows that in both studies simple bimolecular processes were being examined. Also discussed are the possible experimental and theoretical ramifications of these new results.
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  • 8
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Absolute rate constants for the reaction of S(3P) with ethylene episulfide were measured over a C2H4S concentration range of 5, a total pressure of 20-200 tort, and a flash intensity range of ˜4. Over this range of variables, the bimolecular rate constant was found to be invariant. Because of limitations imposed by the physical properties of the reactant C2H4S, temperature variations were necessarily held to the range 298-355°K. The bimolecular rate constant was found to be invariant over this limited temperature range, having a value of (4.47 ± 0.26) × 10-11 cm3 molec.-1 sec-1. The possible influence of this reaction in studies of the S(3P)-ethylene system are discussed.
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  • 9
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Using the technique of flash photolysis-resonance fluorescence, absolute rate constants have been measured for the reaction H + O2 + M → HO2+M over a temperature range of 220-360°K. Over this temperature range, the data could be fit to an Arrhenius expression of the following form: \documentclass{article}\pagestyle{empty}\begin{document}$$k_{{\rm Ar}} = (6.75{\rm } \pm {\rm }1.1){\rm } \times {\rm }10^{ - 33} \exp {\rm }[685{\rm } \pm {\rm }128{\rm cal/mole]/}RT$$\end{document} The units for kAr are cm6/mole-s. At 300°K the relative efficiencies for the third-body gases Ar:He:H2:N2:CH4 were found to be 1.0:0.93:3.0:2.8:22. Wide variations in the photoflash intensity at several temperatures demonstrated that the reported rate constants were measured in the absence of other complex chemical processes.
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  • 10
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    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.
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