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• Physical Chemistry  (766)
• 1975-1979  (477)
• 1970-1974  (289)
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• 1
Electronic Resource
New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: A kinetic study of the oxidation of allyl alcohol by potassium hexacyanoferrate (III) in the presence of palladium (II) chloride is reported. The reaction was observed by measuring the disappearance of the potassium hexacyanoferrate (III) spectrophotometrically. The reaction is first order with respect to allyl alcohol and palladium (II) chloride, inverse second order with respect to [Cl-], and zero order with respect to potassium hexacyanoferrate (III). The rate is found to increase linearly with hydroxyl ion concentration.
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• 2
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Mixtures of Cl2, CH4, and O2 were flash photolyzed at room temperature and pressures of ∽60-760 Torr to produce CH3O2. The CH3O2 radicals decay by the second-order process with k6 = (3.7 ± 0.3) × 10-13 cm3/sec in good agreement with other studies. This value ignores any removal by secondary radicals produced as a result of reaction (6), and therefore the true value might be as much as 30% lower. The value is independent of total pressure or the presence of H2O vapor. With SO2 also present, the CH3O2 decay becomes pseudo first order at sufficiently high SO2 pressure which indicates the reaction The value of (8.2 ± 0.5) × 10-15 cm3/sec at about 1 atm total pressure (mostly CH4) was found for CH3O2 removal by SO2, in good agreement with another recent measurement. This value can be equated with k1, unless the products rapidly remove another CH3O2 radical, in which case k1 would be a factor of 2 smaller.
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• 3
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The kinetics of chlorine transfer from CH2Cl2, CHCl3, CCl4, and CCl3CN to the triethylsilyl radical was studied in the liquid phase by a competitive method. Br abstraction from 1-bromopentane was used as a reference. The following Arrhenius parameters were determined:where the error limits are two standard deviations (2σ). Based on these results, the observed reactivity trends in the chlorine transfer reactions of Et3Si radicals appear to primarily reflect the variation in entropy of activation rather than in activation energies.
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• 4
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Methylperoxy radicals were generated by the flash photolysis of azomethane-oxygen mixtures. The observed broadband spectrum of the CH3O2 radical is similar, but not identical to those reported previously. The CH3O2 decay followed second-order kinetics at high CH3O2 concentrations with k4' = (2.5 ± 0.3) × 108 liter/mol·sec (23 ± 2°C); 2CH3O2 → products (4). Because of the potential loss of CH3O2 through the reactions with HO2 and CH3O radicals subsequently formed in this system, simulations suggest that the true k4 is in the range: 2.5 × 108 ≥ k4 ≥ 2.3 × 108 liter/mol·sec. Deviations from linearity of the plot of the reciprocal of the CH3O2 absorbance versus time were seen at long times and were attributed to the reaction (5) with an apparent rate constant k5' ⋍ (1.6 ± 0.4) × 105 liter/mol·sec; CH3O2 + Me2N2 → product (5). The CH3O2-SO2 reaction, CH3O2 + SO2 → products (16), was studied by observing CH3O2 decay in flashed mixtures of Me2N2, O2, and SO2. The results gave the apparent second-order rate constant k16' ⋍ (6.4 ± 1.4) × 106 liter/mol·sec. It appears likely that each occurrence of reaction (5) and (16) is followed by the loss of an additional CH3O2 radical and that k5 ⋍ k5'/2 and k16 ⋍ k16'/2. Our findings suggest that a significant fraction of the SO2 oxidation in a sunlight-irradiated NOx-RH-polluted atmosphere, may occur by reaction with CH3O2 as well as from the HO and HO2 reactions.
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• 5
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: It is shown that it is possible to obtain good data for the rate constant for the decomposition of alkoxy radicals [RO] by using nitric oxide as a radical trap. Two experimental systems have been used.The first system involves the use of dialkyl peroxides [(RO)2] as thermal sources of alkoxy radicals. The peroxide concentration was ∼10-4M, nitric oxide ∼2 × 10-4M, and the extent of reaction was ∼10%. The total pressure was altered using carbon tetrafluoride as an inert gas. The mechanism is Hence R2/R3 = k2[NO]/k3. Our previous studies show that k2 lies in the range 1010.3±0.2M-1·sec-1.The second system employs alkyl nitrites [RONO] as a thermal source of alkoxy radicals. The experimental conditions are very similar, except that we chose to use an atmosphere of nitric oxide for initial experiments. If anything nitric oxide appears to be superior to carbon tetrafluoride as an energy transfer agent. The mechanism is Hence R3 = k1'k3[RONO]/(k3 + k2 + k6 [NO]).Results are given for R = t-Am, s-Bu, t-Bu, i-Pr, Et, and Me. In addition the first unequivocal evidence is given for the pressure dependence of k3 when R = t-Bu. The implications for atmospheric chemistry and combustion are also discussed.
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• 6
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The thermal decomposition of azomethane in the presence of propene has been investigated in the range of 568-638°K at reactant partial pressures of up to about 7 torr in the presence of at least 170 torr of argon. The elementary reactions taking place in such conditions are discussed in detail. It is shown that a situation approaching equilibrium is attained between the processes Values are obtained for the equilibrium constant K2, which can be described by the equation \documentclass{article}\pagestyle{empty}\begin{document}$${\rm logK}_{\rm 2} \left({{\rm atm}} \right){\rm = 7}{\rm .66 - 26}{\rm .1kcal/mol/(2}{\rm .3RT)}$$\end{document} Using the best available thermodynamic parameters for methyl and propene, it is concluded that those for s-butyl are in need of adjustment. We recommend the values ΔHf0 (300°K) = 13.8 ± 1.0 kcal/mol and S3000 (1 atm standard state) = 75.6 ± 3.0 cal/mol°K together with group additivity values of the heat capacity. A comparison of measured values of K2 with values calculated from independent measurements of k2 and k-2 shows a discrepancy of about a factor of 3.5.
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• 7
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The removal of *UF6 (A state) molecules by selected alkanes has been investigated at 25°C. The following rate constants (units of 1011 l/mol·sec) were evaluated: iso-C4F10, 0.0432 ± 0.0115; n-C4F10, 0.0764 ± 0.020; C2F6, 0.0192 ± 0.0052; CH4, 0.0612 ± 0.0061; C2H6, 3.78 ± 0.60; C3H8, 5.08 ± 0.60; n-C4H10, 5.05 ± 0.78; iso-C4H10, 4.17 ± 1.15; neo-C5H12, 6.59 ± 0.93; CF3—CH3, 0.0385 ± 0.0056; CF2H—CF2H, 0.0729 ± 0.0074; and CF2H—CFH2, 0.149 ± 0.015. The perfluoro-alkane quenching of *UF6 proceeds via a physical mechanism. The other alkane quenching reactions are consistent with a chemical mechanism also contributing in varying degrees which may involve removal of two hydrogens from the alkane.
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• 8
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The cyclization of the 5-hexenyl radical to form the cyclopentylmethyl radical has been reexamined by kinetic EPR spectroscopy at temperatures between 183 and 232°K in cyclopropane solvent. The rate constant, kc for this important radical rearrangement can be represented by \documentclass{article}\pagestyle{empty}\begin{document}$$\log k_c (\sec ^{ - 1}) = (9.5 \pm 1.1) - (6.1 \pm 1.1)/\theta$$\end{document} where Θ = 2.3RT kcal/mol.
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• 9
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Rate, equilibrium, and thermodynamic data for reaction (1) of 2,6-diphenyl-4R-phenoxyl radicals, where R==OCH3 (I), Ph (II), OC2H5 (III), O-n-C18H37 (IV), and 2,6-dicyclohexyl-4-phenylphenoxyl radical (V), in various solvents are obtained. The k1 values of radicals I to V are within (5.5 ± 1.0) × 107-(1.4 ± 0.3) × 109M-1·sec-1 in propanol. The solvent effect on k1 for radicals I and II was studied. The dimerization of radical I is diffusion-controlled in all solvent studies. The dimerization of radical II is viscosity-dependent but not diffusion-controlled. Plots of k1 against ET have a V shape. Specific solvent-solute interactions are seeming to be responsible for numerical k1 values of radicals I and II. The solvent effect is more pronounced for “slow” dimerization of radicals II than for “fast” dimerization of radicals I. The minimum k1 values correspond to pyridine and chloroform. The reaction (1) rate strongly depends upon the composition of a chloroform (S)-cosolvent binary mixture. Besides reaction (1) the following reactions proceed in binary mixture: \documentclass{article}\pagestyle{empty}\begin{document}$$K_{14} = 0.18 \pm 0.05M^{ - 1},k_{15} = (2.0 \pm 1.0) \times 10^8 M^{ - 1} \cdot \sec ^{ - 1}$$\end{document} (radical I, S-CCL4 mixture) \documentclass{article}\pagestyle{empty}\begin{document}$$K_{14} = 0.9 \pm 0.2M^{ - 1},k_{15} = (1.2 \pm 0.5) \times 10^7 M^{ - 1} \cdot \sec ^{ - 1}$$\end{document}(radical II, S-C6H14 mixture) \documentclass{article}\pagestyle{empty}\begin{document}$$K_{14} = 0.45 \pm 0.10M^{ - 1},k_{15} = (9.0 \pm 2.0) \times 10^6 M^{ - 1} \cdot \sec ^{ - 1}$$\end{document}(radical II, S-CCL4 mixture)In all cases k16 ≪ k15. Factors influencing dimerization rates in strongly nonideal mixtures CH3OH-CCL4 and CH3OH-CHCl3 are discussed.
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• 10
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: An algorithm for the automatic sensitivity analysis of kinetic mechanisms based on the Fourier amplitude sensitivity test (FAST) method of Shuler and co-workers is reported. The algorithm computes a measure of the relative sensitivity of each concentration to each parameter of interest, such as rate constants, Arrhenius parameters, stoichiometric coefficients, and initial concentrations. Arbitrary variations in the magnitude of the parameters are allowable. The algorithm is illustrated for the simple example of computing the sensitivity of the concentration of species A to variation of the two Arrhenius parameters for the hypothetical reaction A + A →.
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• 11
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The reactions of ground-state oxygen atoms with carbonothioicdichloride, carbonothioicdifluoride, and tetrafluoro-1,3-dithietane have been studied in a crossed molecular jet reactor in order to determine the initial reaction products and in a fast-flow reactor in order to determine their overall rate constants at temperatures between 250 and 500 K. These rate constants arek(O + C2CS) =(3.09 ± 0.54) × 10-11 exp(+115 ± 106 cal/mol/RT),k(O + F2CS) = (1.22 ± 0.19) × 10-11 exp(-747 ± 95 cal/mol/RT), andk(O + F4C2S2) = (2.36 ± 0.52) × 10-11 exp(-1700 ± 128 cal/mol/RT) cm3/molec·sec. The detected reaction products and their rate constants indicate that the primary reaction mechanism is the electrophilic addition of the oxygen atom to the sulfur atom contained in the reactant molecule to form an energy-rich adduct which then decomposes by C-S bond cleavage.
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• 12
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: 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 \documentclass{article}\pagestyle{empty}\begin{document}$${log k(sec}^{{ - 1}} {) = 17}{.3 - 80}{.8/}\theta { at 1000 K }$$\end{document} are consistent with δHf0(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.
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• 13
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The products of the heterogeneous reactions of chlorine atoms and chlorine oxide radicals with acid coated Pyrex walls have been directly determined for the first time. Contrary to the usual assumption that chlorine atoms recombine to form Cl2, we find that the major product is HCl, with small amounts of perchlorate also formed. Similarly, ClO radicals form HCl rather than Cl2. The source of hydrogen for these reactions is probably the water always found in this type of vacuum system. These results may change the interpretation of flow tube experiments with chlorine atoms. Application to the H + HCl reaction is discussed as an example.
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• 14
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The reactions of S + OH → SO + H (1) and SO + OH → SO2 + H (2) were studied in a discharge flow reactor coupled to an EPR spectrometer. The rate constants obtained under the pseudo-first-order conditions with an excess of S or SO were found to be k1 = (6.6 ± 1.4) × 10-11 and k2 = (8.4 ± 1.5) × 10-11 at room temperature. Units are cm3/molec·sec. Besides no reactivity was observed between S and CO2 at 298 K and between CIO and SO2 up to 711 K.
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• 15
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
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• 16
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The rate constant for the bimolecular combination of benzyl radicals in cyclohexane and toluene is determined as a function of temperature. Further, it is studied in cyclohexane-toluene mixtures of different compositions. In the entire range covered, 9.8 × 108 ≤ 2kt ≤ 9.0 × 109M-1·sec-1, the data are very well described by the Smoluchowski equation for a diffusion-controlled reaction to ground-state products using a spin statistical factor of 1/4, a temperature- and solvent-independent reaction distance, and the known diffusion coefficient of toluene.
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• 17
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Initial rates of formation of primary products have been measured in the pyrolysis of ethylene at 500°C, and a mechanism for the reaction is proposed based on the isomerization of the n-hexyl radical. Additions of oxygen in amounts less than 0.1% markedly increased the rate of formation of all products, but oxygen was not completely consumed in the reaction. It is shown that secondary initiation processes are important at very low conversions, and butene-1 is the most reactive product. Bimolecular reactions between olefins and with oxygen are important steps in the mechanism.
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• 18
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The reaction between NO(g) at concentrations between 0.1 and 1.0 Torr in 1-atm N2 and aqueous solutions of NaClO has been studied over the pH range of 6-12 and hypochlorite concentrations between 0.01 and 1.0M. A very rapid and efficient reaction occurs leading to the production of about 30%-40% of the NO as NO2 and with conversions of NO up to 98% at about 1-sec contact time. It is shown that a fast chain reaction initiated by the endothermic step can account for the data. The very exothermic reaction NO + ClO- → NO2 + Cl- is shown to be at least 30-fold slower than i. The overall reaction seems very promising as a method of reducing NO and NO2 emissions from the exhausts of industrial plants.
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• 19
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The reaction between tris(acetylacetonato)magnanese(III) and hexa(N,N-dimethylformamide)iron(III) perchlorate in acetonitrile proceeds in two stages. The first stage corresponds to the reaction of pentacoordinated Fe(DMF)53+ with Mn(acac)3, and the rate-determining step of the second stage consists mainly in the elimination of a DMF ligand from Fe(DMF)63+ to yield Fe(DMF)53+ which reacts rapidly with the manganese complex. The formation of Fe(DMF)53+ is catalyzed by Mn(acac)3, this catalytic effect being decreased by manganese products. The rate-determining step for the formation of Fe(acac)3 is the transfer of the first acetylacetonate to yield Fe(acac)2+. The final products of iron depend on the ratio of reactant concentrations. With Mn or Fe in excess, Fe(acac)3 or Fe(acac)2+ are mainly produced.
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• 20
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New York, NY : Wiley-Blackwell
International Journal of Chemical Kinetics 11 (1979), S. 1071-1080
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The thermal unimolecular decomposition of hex-1-ene has been investigated over the temperature range of 915-1153 K using the technique of very low-pressure pyrolysis (VLPP). The reaction proceeds via the competitive pathways of C3-C4 fission and retro-ene elimination, with the latter dominant at low temperatures and the former at high temperatures. This behavior results in an isokinetic temperature of 1035 K under VLPP conditions (both reactions in the unimolecular falloff regime). RRKM calculations, generalized to take into account two competing pathways, show that the experimental unimolecular rate constants are consistent with the high-pressure Arrhenius parameters given by log k1 (sec-1) = (12.6 ± 0.2) -(57.7 ± 1.5)/θ for retro-ene reaction, and log k2 (sec-1) = (15.9 ± 0.2) - (70.8 ± 1.0)/θ for C-C fission, where θ = 2.303 RT kcal/mol. The A factors were assigned from the results of a recent shock-tube study of the decomposition in the high-pressure regime, and the activation energies were found by matching the RRKM calculations to the VLPP data. The parameters for C-C fission are consistent with the known thermochemistry of n-propyl and allyl radicals. A clear measure of the importance of the molecular pathway in the decomposition of a mono-olefin has been obtained.
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• 21
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
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• 22
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New York, NY : Wiley-Blackwell
International Journal of Chemical Kinetics 11 (1979), S. 1183-1196
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: By allowing dimethyl peroxide (10-4M) to decompose in the presence of nitric oxide (4.5 × 10-5M), nitrogen dioxide (6.5 × 10-5M) and carbon tetrafluoride (500 Torr), it has been shown that the ratio k2/k2′ = 2.03 ± 0.47: CH3O + NO → CH3ONO (reaction 2) and CH3O + NO2 → CH3ONO2 (reaction 2′). Deviations from this value in this and previous work is ascribed to the pressure dependence of both these reactions and heterogeneity in reaction (2). In contrast no heterogeneous effects were found for reaction (2′) making it an ideal reference reaction for studying other reactions of the methoxy radical. We conclude that the ratio k2/k2′ is independent of temperature and from k1 = 1010.2±0.4M-1 sec-1 we calculate that k2′ = 109.9±0.4M-1 sec-1. Both k2 and k2′ are pressure dependent but have reached their limiting high-pressure values in the presence of 500 Torr of carbon tetrafluoride. Preliminary results show that k4 = 10.9.0±0.6 10-4.5±1.1/ΘM-1 sec-1 (Θ = 2.303RT kcal mole-1) and by k4 = 108.6±0.6 10-2.4±1.1/ΘM-1 sec-1: CH3O + O2 → CH2O + HO2 (reaction 4) and CH3O + t-BuH → CH3OH + (t-Bu) (reaction 4′).
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• 23
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New York, NY : Wiley-Blackwell
International Journal of Chemical Kinetics 11 (1979), S. 1167-1182
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The homogeneous gas-phase decomposition kinetics of silane has been investigated using the single-pulse shock tube comparative rate technique (T = 1035-1184˚K, Ptotal ≍ 4000 Torr). The initial reaction of the decomposition SiH4 \documentclass{article}\pagestyle{empty}\begin{document}${\rm SiH}_{\rm 4} \mathop \to \limits^1 {\rm SiH}_{\rm 2} + {\rm H}_{\rm 2}$\end{document} SiH2 + H2 is a unimolecular process in its pressure fall-off regime with experimental Arrhenius parameters of logk1 (sec-1) = 13.33 ± 0.28-52,700 ± 1400/2.303RT. The decomposition has also been studied at lower temperatures by conventional methods. The results confirm the total pressure effect, indicate a small but not negligible extent of induced reaction, and show that the decomposition is first order in silane at constant total pressures. RRKM-pressure fall-off calculations for four different transition-state models are reported, and good agreement with all the data is obtained with a model whose high-pressure parameters are logA1 (sec-1) = 15.5, E1(∞) = 56.9 kcal, and ΔE0±0(1) = 55.9 kcal. The mechanism of the decomposition is discussed, and it is concluded that hydrogen atoms are not involved. It is further suggested that silylene in the pure silane pyrolysis ultimately reacts with itself to give hydrogen: 2SiH2 → (Si2H4)* → (SiH3SiH)* → Si2H2 + H2. The mechanism of H ↔ D exchange absorbed in the pyrolysis of SiD4-hydrocarbon systems is also discussed.
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• 24
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New York, NY : Wiley-Blackwell
International Journal of Chemical Kinetics 11 (1979), S. 1211-1229
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Intrinsic spectral and kinetic parameters have been measured for the ethylperoxy radical, which was formed in the gas phase by the flash photolysis of azoethane in the presence of an adequate excess of oxygen. Absolute values of the extinction coefficient ∊(λ) were derived from complementary measurements of the yield of nitrogen and the absorbance of an equivalent concentration of ethylperoxy radicals. The absorption spectrum is broad, structureless and comparatively weak; ∊(236) = 1.02 × 103 liter mole-1 cm-1 at the maximum, and the oscillator strength is 3.4 × 10-2. This spectrum resembles the spectrum of the methylperoxy radical closely in form, but it is less intense; the ratio of the values of oscillator strength is 0.5. The bimolecular reactions of mutual interaction of ethylperoxy radicals are not exclusively terminating, and ethoxy and hydroperoxy radicals are formed in kinetically significant quantities. A computer program was designed to simulate the rise and fall of the concentration of each radical species, and to perform the related kinetic analysis. This program predicted that a second-order plot of the decline of the absorbance of the ethylperoxy radical during the dark period would not show a significant departure from linearity, a conclusion which was confirmed by experiment. Accordingly, the gradient of each such plot yielded a value of k'/∊(λ), where k' is the apparent value of the rate constant for the collective reactions of mutual interaction. This rate constant was evaluated from the product of corresponding values of k'/∊(λ) and ∊(λ); individual values are independent of the wavelength of measurement, and the mean value is k' = (6.6 ± 0.5) × 107 liter mole-1 sec-1. Further kinetic analysis yielded the corresponding absolute value: k = (6.0 ± 0.6) × 107 liter mole-1 sec-1. This value fits the pattern of a relationship between rate constant and structure shown by the methylperoxy, isopropylperoxy, and tert-butylperoxy radicals. Adequate sensitivity for the characterization of the spectrum of the ethylperoxy radical was achieved by the use of a pulsed xenon arc as the monitoring light source in conjunction with a dual beam detection system with twin cells and balanced photomultipliers, and the apparatus is described in detail.
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• 25
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New York, NY : Wiley-Blackwell
International Journal of Chemical Kinetics 11 (1979), S. 1271-1278
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Experimental evidence is presented for a unimolecular gas-phase Wagner-Meerwein shift in neopentyl chloride pyrolysis. In the decomposition of α,α-neopentyl chloride-d2 at 445°C, maximally inhibited by cyclohexene, the initial products were isotopically pure 2-methyl-1-butene-d2 and 2-methyl-2-butene-d1. Rearrangement, accompanied by loss of either α- or γ-hydrogen in the formation of hydrogen chloride, is consistent with an incipient ion-pair type of transition state. The cyclohexene maximally inhibited pyrolysis of neopentyl chloride was also examined over the temperature range 424-478°C and Arrhenius parameters of E, 258.7 kJ/mole and logA/sec-1, 13.78, were determined.
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• 26
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New York, NY : Wiley-Blackwell
International Journal of Chemical Kinetics 11 (1979), S. 1279-1286
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: 4-Chloro-1-butene, 5-chloro-1-pentene, and 6-chloro-1-hexene have been shown to decompose, in a static system, mainly to hydrogen chloride and the corresponding alkadienes. In packed and unpacked clean Pyrex vessels the reactions were significantly heterogeneous. However, in a vessel seasoned with allyl bromide these reactions were homogeneous, unimolecular, and follow a first-order law. The working temperature range was 389.6-480.0°C and with a pressure range of 53-221 Torr. The rate constants for the homogeneous reactions were expressed by the following Arrhenius equations: 4-chloro-1-butene: logk(sec-1) = (13.79 ± 0.17) - (223.8 ± 2.1)kJ/mole/2.303RT; 5-chloro-1-pentene: logk(sec-1) = (14.25 ± 1.20) - (238.4 ± 12.7)kJ/mole/2.303RT; and 6-chloro-1-hexene: logk(sec-1) = (12.38 ± 0.22) - (209.6 ± 2.9)kJ/mole/2.303RT. The olefinic double bond has been found to participate in the rate of dehydrohalogenation of 4-chloro-1-butene. The insulation of the CH2=CH in chlorobutene by one or two methylene chains to the reaction center does not indicate neighboring group participation. The three-membered conformation is the most favored structure for anchimeric assistance of the double bond in gas phase pyrolysis of alkenyl chlorides. The heterolytic nature of these eliminations is also supported by the present work.
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• 27
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Notes: The oxidation of fluorene by vanadium(V) in aqueous acetic acid containing sulfuric acid (1.0M) at 50°C produces fluorenone and 2-hydroxy diphenyl 2′-carboxaldehyde. The order with respect to each reactant is found to be 1. The order dependence on sulfuric acid concentration is 4, indicating that V(OH)23+ could be the active species. An increase in the acetic acid percentage in the solvent medium increases the rate of the reaction. The effect of solvent variation has been discussed in the light of the acidity function and the polarity of the medium. The effect of substituents on the rate has been studied for seven substituted fluorenes, and a linear relationship exists between log k versus σ values with the slope ρ = -3.2. A small isotope effect is observed for the oxidation of the parent compound (kH/kD = 1.2). The effect of temperature on the rate of the reaction has been studied, and the activation parameters are discussed. A mechanism involving the rate-limiting formation of a cation-radical intermediate is proposed.
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• 28
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Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
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• 29
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Source: Wiley InterScience Backfile Collection 1832-2000
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Notes: The Arrhenius parameters for the title reaction have been measured in a very-low-pressure pyrolysis apparatus in the temperature range 644-722 K and are given by log k2 (M-1 · sec-1) = 9.68 - 2.12/θ, where θ = 2.303RT in kcal/mol. Together with the published Arrhenius parameters for the reverse reaction from iodination studies, they result in a standard heat of formation of the t-butyl radical of 8.4 kcal/mol, accepting S0(C4H9·) = 72.2 e.u. at 300 K from other kinetic data, and thus confirm the accepted value for ΔHf0(t-C4H9·), at variance with recent investigations which yielded significantly higher values. This value for ΔHf0(t-C4H9·) results in a bond-dissociation energy (BDE) for isobutane of 92.7 kcal/mol.
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• 30
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International Journal of Chemical Kinetics 11 (1979), S. 1045-1053
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Using dimethyl peroxide as a thermal source of methoxy radicals overthe temperature range of 110-160°C, and the combination of methoxy radicals and nitrogen dioxide as a reference reaction: a value was determined of the rate constant for the reaction of methoxy radicals with oxygen: is independent of nitrogen dioxide or oxygen concentration and added inert gas (carbon tetrafluoride). No heterogeneous effects were detected. The value of k4 is given by the expression \documentclass{article}\pagestyle{empty}\begin{document}$${\rm log }k_4 {\rm = 9}{\rm .0} \pm {\rm 0}{\rm .6 - 4}{\rm .8 } \pm {\rm 1}{\rm .1/}\theta {\rm (M}^{{\rm - 1}} \cdot \sec ^{ - 1})$$\end{document} In terms of atmospheric chemistry, this corresponds to a value of 105.6 M-1·sec-1 at 298 K. Extrapolation to temperatures where the combustion of organic compounds has been studied (813 K) produces a value of 107.7 M-1·sec-1 for k4. Under these conditions, reaction (4) competes with hydrogen abstraction or disproportionation reactions of the methoxy radical and its decomposition (3): In particular k3 is in the falloff region under these conditions. It is concluded that reaction (4) takes place as the result of a bimolecular collision process rather than via the formation of a cyclic complex.
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• 31
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International Journal of Chemical Kinetics 11 (1979), S. 1097-1108
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: A portable program package, MACKSIM, for mass action chemical kinetics simulation, is discussed. As these kinetics are readily expressed in explicit mathematical terms, such a package contains two major and distinct modules, the numerical analysis and the user interface. For the first, MACKSIM uses the latest proven developments incorporating sparse matrix techniques in the backward difference predictor corrector methods originated by Gear for the integration of stiff ordinary differential equations, and thus requires minimal computing time to solve large systems of equations. For the second, the program provides a flexible interface which permits simple specification and variation of reactions, requires no special character input, and has no limit on the number of reactions or species involved other than that imposed by the size of the computer. The technology of these components is discussed briefly, the use of the package for standard reactions is illustrated, and current applications are mentioned.
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• 32
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International Journal of Chemical Kinetics 11 (1979), S. 1133-1133
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
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• 33
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International Journal of Chemical Kinetics 11 (1979), S. 1163-1166
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The structure of t-Bu3SiċH2, (I), suggested that it might be a persistent primary alkyl radical since it has (i) a bulky group to protect the radical center; (ii) no β-hydrogens, so that a radical-radical disproportionation reaction is impossible; (iii) a β-silicon atom, which should prevent β-scission of tert-butyl as a unimolecular decomposition pathway. However, the self-reaction of (I) in isooctane was found to be a diffusion controlled process with log(A/M-1 sec-1) = 10.7 ± 0.3 and E = 2.5 ± 0.2 kcal mole-1. Hence (I) is not persistent and it is concluded that a persistent primary alkyl will only be observed when the - ĊH2 moiety is deeply buried among sterically protecting groups.
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• 34
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• 35
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International Journal of Chemical Kinetics 11 (1979), S. 1263-1269
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The gamma-radiation-induced free-radical chain reactions in liquid CCl4—C2Cl4—c—C6H12 mixtures were studied in the temperature range of 363-448°K. The main products in this system are chloroform, hexachloropropene and chlorocyclohexane. These products are formed via reactions (1)-(5): with G values (molec/100 eV) of the order of magnitude of 102 and 103 at the lowest and highest temperatures, respectively. Values of k2/k1 were determined from the product distribution. In turn, these values gave the following Arrhenius expression for k2/k1 (θ = 2.303RT, in kcal/mol): \documentclass{article}\pagestyle{empty}\begin{document}$${\rm log }\,k_2 /k_1 = ( - 1.21 + 0.10) + (1.59 \pm 0.27)/\theta$$\end{document} From this result and the previously determined Arrhenius parameters of reaction (1), k2 is found to be given by \documentclass{article}\pagestyle{empty}\begin{document}$${\rm log }\,k_2 (1/{\rm mol} \cdot {\rm sec) = 7}{\rm .58 - 9}{\rm .49/}\theta$$\end{document}.
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• 36
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International Journal of Chemical Kinetics 11 (1979), S. 1297-1299
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: No. Abstract.
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• 37
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Notes: The flash photolysis resonance fluorescence technique has been utilized to determine the rate constants for three reactions involving the hydroxyl radical [OH(2≅)] and three halogenated C2 alkanes. The nominal temperature range covered was 250-375 K. The compounds studied and the resulting Arrhenius expressions in units of cm3/molec·sec are The error limits in these expressions are such that they include any possible systematic errors due to the presence of impurities in the halocarbon samples. Tropospheric lifetimes have been calculated for the above species by combining the above rate constant data with global seasonally and diurnally averaged hydroxyl radical concentrations.
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• 38
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Notes: A detailed mechanism is presented for reactions occurring during irradiation of part-per-million concentrations of propene and/or n-butane and oxides of nitrogen in air. Data from an extensive series of well-characterized smog chamber experiments carried out in our 5800-liter evacuable chamber-solar simulator facility designed for providing data suitable for quantitative model validation were used to elucidate several unknown or uncertain kinetic parameters and details of the reaction mechanism.The mechanism was then tested against the data base from the smog chamber runs. In general, most calculated concentration-time profiles agreed with experiments to within the experimental uncertainties. Fits were usually attained to within ∼±20% or better for ozone, NO, propene, and n-butane, to within ∼±30% or better for NO2, PAN, methyl ethyl ketone, 2-butyl nitrate, butyraldehyde, and (in runs not containing propene) methyl nitrate, to within ⋐±50% or better for the minor products 1-butyl nitrate and propene oxide, and to within a factor of 2 for methyl nitrate in propene-containing runs. Propionaldehyde was consistently underpredicted in all runs; it is probably a chamber contaminant. For formaldehyde and acetaldehyde, the major products in both systems, fits to within ⋐±20% were often obtained, yet for a number of experiments, significantly greater discrepancies were observed, probably as a result of experimental and/or analytical problems.The good fits to experimental data were attained only after adjusting several rate constants or rate constant ratios related to uncertainties concerning chamber effects or the chemical mechanism. The largest uncertainty concerns the necessity to include in the mechanism a significant rate of radical input from unknown sources in the smog chamber. Other areas where fundamental kinetic and mechanistic data are most needed before a predictive, detailed propene + n-butane-NOx-air smog model can be completely validated concern other chamber effects, the O3 + propene mechanism, decomposition rates of substituted alkoxy radicals, primary quantum yields for radical production as a function of wavelength for aldehyde and ketone photolyses, and the mechanisms and rates of reactions of peroxy radicals with NO and NO2.
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• 39
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Notes: Relaxation rates for O2(1Σg+) by nonradiative pathways have been determined using the fast-flow technique. O2(1Σg+) is formed from O2(1Δg) by an energy pooling process. O2(1Δg) is generated by passing purified oxygen through a microwave discharge. Oxygen atoms are removed by distilling mercury vapor through the discharge zone. It has been observed that the wall loss rate for O2(1Σg+) decreases with increasing pressure of oxygen and thus appears to be diffusion controlled. Quenching rate constants for O2, N2, and He have been determined and found to be (1.5 ± 0.1) × 104, (1.0 ± 0.05) × 106 and (1.2 ± 0.1) × 105 l./mol·sec, respectively.
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• 40
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Notes: The kinetics of oxidation of glycine, alanine, phenylalanine, serine threonine, aspartic, and glutamic acid by acid permanganate were investigated to elucidate the mechanism of the reactions. The rate law was found to be \documentclass{article}\pagestyle{empty}\begin{document}$$\frac{{ - d[Mn\left({VII} \right)]}}{{dt}} = k_0 [a\min oacid][Mn\left({VII} \right)]$$\end{document} The reactions were found to be acid catalyzed, and the kinetic data indicate the participation of the water molecules in the rate-determining step as a proton-abstracting agent from the substrate, as per Bunnett's hypothesis. As Ag+ was found to catalyze these reactions, the oxidation of glycine and glutamic acid was studied, and the rate law was found to be \documentclass{article}\pagestyle{empty}\begin{document}$$\frac{{ - d\ln [Mn\left({VII} \right)]}}{{dt}} = \frac{{Kk_c^{''} [a\min oacid][Ag^ +]}}{{1 + K[a\min oacid] = K[Ag^ +]}}$$\end{document} A probable mechanism consistent with the observed results is discussed.
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• 41
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Notes: Particle times of flight in incident shock flow were determined experimentally by marking several positions of the test gas (mainly Ar) in the shock tube with an infrared emitting gas (NO or CO2). From the local particle velocity, derived from the particle flight times, temperature and pressure changes behind the shock front were evaluated. Several experimental data were found to be correctly described by Mirels's formulations when used properly. The limitations of the formulations are discussed. It is found to be advisable to evaluate boundary-layer effects on shock-tube flow by experiments, rather than theory, in carrying out chemical kinetics studies.
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• 42
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• 43
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Notes: In the radiolysis of water vapor containing small concentrations of cyclohexane, the principal products which account for about 98% of all end products are found to be hydrogen, cyclohexene, and bicyclohexyl. Cyclohexene and bicyclohexyl yields were determined over a range of temperatures (70-200°C), total pressures (50-2400 torr), and total doses (0.15-2.0 Mrad). The disproportionation-combination ratio kdH/kcH for c-C6H11 radicals could be determined as 0.56 ± 0.01 from the ratio of cyclohexene to bicyclohexyl yield. By using c-C6D12, the ratio kdD/kcD for c-C6D11 radicals is found to be 0.38 ± 0.01. Comparison of the reactivity pattern of C6H11 and C6D11 radicals leads to (kdH)/(kcH)/(kdD/kcD) = 1.47 ± 0.02. The corresponding values for the reactions of c-C6H11 with c-C6D11 were also determined.
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• 44
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Notes: Analysis is made of reported results on the kinetics and mechanism of ascorbic acid oxidation with oxygen in the presence of cupric ions. The diversities due to methodological reasons are cleared up. A kinetic study of the mechanism of Cu2+ anaerobic reaction with ascorbic acid (DH2) is carried out. The true kinetic regularities of catalytic ascorbic acid oxidation with oxygen are established at 2.7 ≤ pH 〈 4, 5 × 10-4 ≤ [DH2] ≤ 10-2M, 10-4 ≤ [Cu2+] ≤ 10-3M, and 10-4 ≤ [O2] ≤ 10-3M: \documentclass{article}\pagestyle{empty}\begin{document}$${\rm W}_0 = {}_{K1}[{\rm Cu}^{{\rm 2} +}][{\rm DH}_2][{\rm O}_2]{}^{0.5}/[{\rm H}^ +]$$\end{document} wherek1 (25°C) = 0.13 ± 0.01 M-0.5·sec-1. The activation energy for this reaction is E1 = 22 ± 1 kcal/mol. It is found by means of adding Cu+ acceptors (acetonitrile and allyl alcohol) that the catalytic process is of a chain nature. The Cu+ ion generation at the interaction of the Cu2+ ion with ascorbic acid is the initiation step. The rate of the chain initiation at [Cu2+] ± 10-4M, [DH2] ± 10-2M, 2.5 〈 pH 〈 4, is \documentclass{article}\pagestyle{empty}\begin{document}$${\rm W}_{\rm i} = {}_{K{\rm i,1}}[{\rm Cu}^{{\rm 2} +}]^2 [{\rm DH}_2]/[{\rm H}^ +]$$\end{document} whereki,1 (25°C) = (1.8 ± 0.3)M-1·sec-1, Ei,1 = 31 ± 2 kcal/mol. The reaction of the Cu+ ion with O2 is involved in a chain propagation, so that the rate of catalytic ascorbic acid oxidation for the system Cu2+—DH2—O2 is \documentclass{article}\pagestyle{empty}\begin{document}$${\rm W}_{\rm 0} = {}_{k{\rm 1}}[{\rm Cu}^ +][{\rm O}_2]$$\end{document} wherek1 (25°C) = (5 ± 0.5) × 104 M-1·sec-1. The Cu+ ion and a species interacting with ascorbate are involved to quadratic chain termination. By means of photochemical and flow electron spin resonance methods we obtained data characteristic of the reactivities of ascorbic acid radicals and ruled out their importance for the catalytic chain process. A new type of chain mechanism of catalytic ascorbic acid oxidation with oxygen is proposed: .
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• 45
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• 46
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Notes: Rate constants for the reaction HO2 + NO2(+ M) = HO2NO2(+ M) have been obtained from direct observations of the HO2 radical using the technique of molecular modulation ultraviolet spectrometry. HO2 was generated by periodic photolysis of Cl2 in the presence of excess H2 and O2, and k1 was determined from the measured concentrations and lifetime of HO2 with NO2 present. k1 increased with pressure in the range of 40-600 Torr, and a simple energy transfer model gave the following limiting second- and third-order rate constants at 283 K: k1∞ = 1.5 ± 0.5 × 10-12 cm3/molec·sec and k1III = 2.5 ± 0.5 × 10-31 cm6/molec·sec. The ultraviolet absorption spectrum of peroxynitric acid was also recorded in the range of 195-265 nm; it showed a broad feature with a maximum at 200 nm, σmax = 4.4 × 10-18 cm2.
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• 47
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Notes: The reaction of methyl radicals with CCl4 and CCl3Br have been reinvestigated in the gas phase over a wide range of temperatures and pressures using both the photolysis of acetone and the pyrolysis of di-tertiary butyl peroxide (dtBP) as the methyl radical sources. The results are in essential agreement with previous work; however, these new studies provide evidence that at higher pressures the major source of HCl in the reactions is due to methyl radical attack on CH3CCl3, formed via the combination of methyl and trichloromethyl radicals.From these investigations Arrhenius parameters for the reactions have been determined: \documentclass{article}\pagestyle{empty}\begin{document}$$k_2 = 10^{8.8 \pm 0.3} {\rm exp - }\left({\frac{{{\rm 10}{\rm .1} \pm {\rm 0}{\rm .5}\,{\rm kcal}}}{{RT}}} \right)1/{\rm mol} \cdot {\rm sec}$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$k_{15} { } = { 10}^{8.1 \pm {0}{.3}} { exp - }\left({\frac{{{3}{.5 } \pm { 0}{.5 kcal}}}{{RT}}} \right){ 1/mol} \cdot {sec}$$\end{document}Pyrolysis of dtBP in the presence of relatively high-pressure mixtures of CCl4 and CCl3Br resulted in no enhanced methane formation, since, under these conditions, the only termination product is C2Cl6, and the HCl precursor CH3CCl3 is not formed. A competitive technique has been used in which dtBP was pyrolysed in the gas phase in the presence of high-pressure mixtures of CCl3Br and a chloromethane. Arrhenius parameters were obtained for the reactions and the results were used to provide information on the importance of polar effects for hydrogen abstraction from halogenated methanes.
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• 48
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Notes: The kinetics of gas-phase elimination of 3-methyl-1-butyl acetate and 3,3-dimethyl-1-butyl acetate into acetic acid and the corresponding substituted butenes have been measured over the temperature range of 360-420°C and the pressure range of 63-250 Torr. The reactions are homogeneous in both clean and seasoned vessels, obey first-order law, and are unimolecular. The temperature dependence of the rate constants is given by the Arrhenius equation3-methyl-1-butyl acetate: \documentclass{article}\pagestyle{empty}\begin{document}$${log k(sec}^{{ - 1}} {) = (12}{.73 } \pm { 0}{.29) - (202}{.5 } \pm { 3}{.8) kJ/mol/2}{.303}RT$$\end{document}3,3-dimethyl-1-butyl acetate: \documentclass{article}\pagestyle{empty}\begin{document}$${log k(sec}^{{ - 1}} {) = (12}{.34 } \pm { 0}{.35) - (194}{.1 } \pm { 4}{.2) kJ/mol/2}{.303}RT$$\end{document} The points in a plot of log (k/k0) of β-alkyl and several β-substituted ethyl acetates against Es values appear aligned in an approximate linear relationship. These results may be interpreted as a consequence of steric effects, namely, steric accelerations.
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Notes: Using the technique of CO2 laser photosensitized decomposition, ethane and propane decomposition was investigated in relation to energy transfer from an SF6 photosensitizer to the hydrocarbon. The end products appearing in the course of irradiation are similar to those formed during classical thermal pyrolysis. The energy transfer from SF6 to the hydrocarbon is closely related to hydrocarbon decomposition. A similar overall kinetic behavior for the two alcanes allows the use of a general diffusional kinetic treatment, provided pressure, intensity, and duration of irradiation are well defined.
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Notes: 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: \documentclass{article}\pagestyle{empty}\begin{document}$$\log k(\sec ^{ - 1}) = 16.2 - 55.2/\theta$$\end{document} 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 kr∞ of 109.7 over the temperature range 300-1000 K.
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Notes: The decomposition of C2H6 in Ar was studied by laser-absorption and laser-schlieren measurements of the reaction rate behind incident shock waves with 1300 〈 T 〈 2500°K and 1.1 〈 ρ 〈 4.4 × 10-6 mol/cm3. The experimental profiles were parameterized by suitable measures of reaction progress. Computer simulations using a 14-reaction mechanism were used to compare assumptions about rate constant expressions with the experimental parameters and to investigate the sensitivity of computed parameters to these assumptions. A rate constant expression k(cm3/mol·sec) = 2 × 10111 T-25.26 exp(-80 320/T) was found for the primary dissociation step C2H6 + M = CH3 + CH3 + M under the conditions studied; no difference in rate was discernable between M = Ar and M = C2H6. Rate constant expressions found to be suitable for the remaining reactions of the mechanism, to some of which the computed parameters were sensitive, were in accord with previous proposals. Our results and results from earlier investigations of the primary decomposition reaction, in both forward and reverse directions, were extrapolated, using RRK methods, to obtain low-pressure limiting rate constants and found to be concordant.
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Notes: The competitive photochlorination and chlorine photosensitized dehydrochlorination of 1,1,1,2-C2H2Cl4 have been studied over the temperature range of 349.4-404.5 K after less than 1% conversion. The results are discussed and a value of \documentclass{article}\pagestyle{empty}\begin{document}$$\log k_{4A} (\sec ^{ - 1}) = (11.6\pm 0.6) - (16,400\pm 1000)/4.58T$$\end{document} is proposed for the reaction \documentclass{article}\pagestyle{empty}\begin{document}$${\rm CCl}_{\rm 3} {\rm CHCl}\mathop \to \limits^{(4{\rm A)}} {\rm CCl}_{\rm 2} {\rm CHCl + Cl}$$\end{document} This result, combined with existing thermochemical data, indicates that there is no evidence of an activation energy for the addition of a Cl atom on the most chlorinated carbon in trichloroethylene: in that case the selectivity of the addition of Cl on the less chlorinated carbon should not depend on temperature.
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Topics: Chemistry and Pharmacology
Notes: Lifetime data have been obtained for the decay of SO2(3B1 0,0,0) at 25°C over the pressure range of 1-762 torr. The 3B1 state was populated by direct absorption to eliminate any possible complications in interpretation due to the participation of excited-singlet manifolds. At pressures greater than about 10 torr, the measured lifetimes are longer than predicted from low-pressure Stern-Volmer parameters. This deviation can be interpreted in terms of Freed's theory on collisionally induced intersystem crossing and provides unequivocal evidence to support earlier speculations that the lengthening of the lifetimes at high pressures is due to saturation in depopulation of the 3B1 state.
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• 54
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The reaction\documentclass{article}\pagestyle{empty}\begin{document}$CH\left({CH_3 } \right)\left({COOH} \right)_2 + I_2 \rightleftharpoons CI(CH_3)\left({COOH} \right)_2 + H^ + + I^ -$\end{document} was followed spectrophotometrically at 353 nm and 470 nm at 25°C under various conditions of pH and methylmalonic acid concentration. The equilibrium constant for the reaction is 0.11 ± 0.02. An iterative technique was used to integrate postulated rate equations. Agreement between experimental and calculated absorbance versus time curves was generally better than 0.005 A (approximately 5% of maximum) at both wavelengths for a mechanism where the rate-determining step is formation of an enolate (k = 1.63 Θ 10-4 ± 0.03 Θ 10-4 sec-1). The enolate may be rapidly transformed to the enol or enol carboxylate anion depending on the pH. All three forms are rapidly iodinated. The mechanism of general base catalysis is supported by rate increases proportional to base concentration in buffer solutions. The bases, acetate ion, chloracetate ion, sulfate ion, dichloracetate ion, and water, follow a Brønsted relationship with β = 0.7.
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• 55
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Intrinsic spectral and kinetic parameters have been measured for the ethyl radical, which was formed in the gas phase by the flash photolysis of azoethane. Absolute values of the extinction coefficient ε(λ) were derived from complementary measurements of the yield of nitrogen and the absorbance of an equivalent concentration of the ethyl radical. The absorption spectrum is broad, structureless, and comparatively weak; ε(247) = 4.8 × 102 l/mol·cm at the maximum, and the oscillator strength is (9.1 ± 0.5) × 10-3. This is in good qualitative agreement with a spectrum obtained independently using the technique of molecular modulation spectrometry.The biomolecular reactions of mutual interaction were the only significant reactions of the ethyl radical in this system; kinetic analysis of the second-order decline of the absorbance during the dark period yielded a value of k/ε(λ) for each experiment. The rate constant for mutual interaction was evaluated from the product of corresponding measurements of k/ε(λ) and ε(λ) individual values are independent of the wavelength of measurement, and the mean value is k = (1.40 ± 0.27) × 1010 l/mol·sec. The rate constant for mutual combination was derived with the aid of product analysis as k2 = (1.24 ± 0.23) × 1010 l/mol·sec; it stands in close agreement with the set of “high” values obtained by direct measurement using a variety of methods.
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• 56
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Our previous mechanistic model for the Belousov-Zhabotinsky reaction has been revised to include a more realistic set of reactions for the oxidation pathways of the organic intermediates. A few other rate constants have also been modified to include new information. The revised mechanism reproduces the essential experimental observations, although the periods of oscillation are somewhat too long and oscillations cease at malonic acid concentrations about ten times greater than the observed lower limit. However, the essential features of the mechanism are clearly understood.
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• 57
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The photolysis was investigated at 313 nm wavelength, 253-529 K temperatures, and 4 × 10-11-2 × 10-9 mol·photon/cm2·sec light intensities by determining the quantum yields of 20 reaction products. Primary quantum yields for the seven primary processes and rate constant ratios, rate constants, and Arrhenius parameters for secondary processes were derived on the basis of the suggested reaction scheme. The dependence of the quantum yields of the four major primary processes on experimental conditions was established.
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• 58
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The kinetics of oxidation of dimethyl sulfoxide (DMSO) by chloramine-T (CAT) is studied in HClO4 and NaOH media with OsO4 as a catalyst in the latter medium. In acid medium, the rate law is -d [CAT]/dt = k [CAT][DMSO][H+]. Alkali retards the reaction and the rate law takes the form -d [CAT]/dt = k [CAT][DMSO][OsO4]/[NaOH], but is reduced to -d [CAT]/dt = k [CAT][DMSO] at higher alkali concentrations. The reaction is subjected to changes in (a) ionic strength, (b) concentrations of added neutral salts, (c) concentrations of added reaction product, (d) dielectric constant, and (e) solvent isotope effect, and the subsequent effects on the reaction rate are studied.The reaction mechanism in acid medium assumes an electrophilic attack by the free acid RNHCl (CAT′) at the sulfur site in DMSO, forming a reaction intermediate which subsequently decomposes to dimethyl sulfone on hydrolysis. Formation of a cyclic complex between RNHCl and OsO4 which interacts with the substrate in a slow step explains the observed results in alkaline medium. The simplification of the rate equation at higher alkali concentrations is attributed to a direct reaction between chloramine-T and the substrate.
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• 59
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Unimolecular rate data from systems such as very-low-pressure pyrolysis (steady-state flow) and static experiments where gas-gas collisions compete with gas-wall collisions must be interpreted in terms of reactant inhomogeneity arising from finite diffusion rates, rather than using the usual assumption of a well-stirred reactor. An integrodifferential equation describing this process is derived, and a numerical variational solution applicable to weak gas-gas collisions is presented. This gives a powerful method for obtaining collisional energy transfer probabilities from such experiments. Previously reported data (on cyclobutane and cycloheptatriene reactions) are reinterpreted to give conventional values for average energy transfer, replacing the anomalously low collisional efficiencies proposed previously.
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• 60
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: A mechanism for ozone-olefin reactions is developed that is consistent with the recent findings of several investigations. These findings suggest a reaction sequence leading to the production of fewer free radical species than has been assumed in the past. Computer simulations using the new mechanism reproduce experimental results obtained from the ozonolysis of propylene in air.
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• 61
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The kinetics of the redox reaction between mandelic acid (MA) and ceric sulfate have been studied in aqueous sulfuric acid solutions and in H2SO4—MClO4 (M+ = H+, Li+, Na+) and H2SO4—MHSO4 (M+ = Li+, Na+, K+) mixtures under various experimental conditions of total electrolyte concentration (that is, ionic strength) and temperature. The oxidation reaction has been found to occur via two paths according to the following rate law: rate = k[MA] [Ce(IV)], where k = k1 + k2/(1 + a)2[HSO4-]2 = k1 + k2/(1 + 1/a)2[SO42-]2, a being a constant. The cations considered exhibit negative specific effects upon the overall oxidation rate following the order H+ ≤ Li+ 〈 Na+ 〈 K+. The observed negative cation effects on the rate constant k1 are in the order Na+ 〈 Li+ 〈 H+, whereas the order is in reverse for k2, namely, H+ ≤ Li+ 〈 Na+. Lithium and hydrogen ions exhibit similar medium effects only when relatively small amounts of electrolytes are replaced. The type of the cation used does not affect significantly the activation parameters.
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• 62
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
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• 63
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The rate constant for the bimolecular combination of trichloromethyl radicals in methanol is determined as a function of temperature by steady-state kinetics and electron-spin resonance with modulated radical initiation. The rate constant is in accord with the Smoluchowski equation and indicates a diffusion-controlled radical termination. The temperature dependence of the rate constant for the electron-transfer reaction between hydroxymethyl radicals and carbon tetrachloride in methanol is determined, and is found to disagree with predictions of the Marcus theory. This disagreement is tentatively ascribed to the structure of the transition state.
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• 64
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The kinetics of the gas-phase thermal iodination of hydrogen sulfide by I2 to yield HSI and HI has been investigated in the temperature range 555-595 K. The reaction was found to proceed through an I atom and radical chain mechanism. Analysis of the kinetic data yields log k (l/mol·sec) = (11.1 ± 0.18) - (20.5 ± 0.44)/θ, where θ = 2.303 RT, in kcal/mol. Combining this result with the assumption E-1 = 1 ± 1 kcal/mol and known values for the heat of formation of H2S, I2, and HI, ΔHf,2980(SH) = 33.6 ± 1.1 kcal/mol is obtained. Then one can calculate the dissociation energy of the HS—H bond as 90.5 ± 1.1 kcal/mol with the well-known values for ΔHf,2980 of H and H2S.
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• 65
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ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Rate constants determined for the thermal dimerization of chlorotrifluoroethene to dichlorohexafluorocyclobutane at 404-672 K have been correlated with previously published results. For the temperature range of 404-800 K, \documentclass{article}\pagestyle{empty}\begin{document}$$k{ = 1}{.08} \times { 10}^{{ - 9}} { T }^{{4}{.02}} { exp ( - 86,700/RT) m}^{3} {/mol} \cdot \sec$$\end{document} The dependence of the preexponential factor on temperature corresponds to a value of 17 J/K·mol for the difference in heat capacity (ΔCp±) between the activation complex and the reactant.
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• 66
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ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The absolute quantum yield of O(1D2) in the photolysis of ozone in the Hartley band, between about 230 and 280 nm, has been determined using the isotopic exchange reaction between C16O2 and 18O(1D2). A value of 1.00 ± 0.05 has been obtained within a 95% confidence limit. A value of unity may therefore be accepted as the average quantum yield of O(1D2) atoms in the 230-280-nm region within an uncertainty of only several percent.
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• 67
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New York, NY : Wiley-Blackwell
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The mutual combination reaction is proposed as the rate-limiting step in the removal of ClO radicals at moderate pressures. The third--order rate constants measured at room temperature were k1(Ar) = 3.51 ± 0.14 × 109 l2/mol2·ec; k1(He) ≈ 2.8 × 109 l2/mol2·sec, and k1(O2) ≈ 7.9 × 109 l2/mol2·sec. There is also an independent second-order reaction for which k3 ≈ 8 × 106 l/mol·sec. A new absorption spectrum has been observed in the ultraviolet and attributed to Cl2O2. The extinction coefficient for Cl2O2 has been measured at six wavelengths, and, between 292 and 232 nm, it increases from 0.4 × 103 to 2.9 × 103 l/mol·cm. In the presence of the chlorine atom scavengers OClO or Cl2O, Cl2O2 exists in equilibrium with ClO. The equilibrium constant Ke1 = 3.1 ± 0.1 × 106 l/mol at 298 K, and, with ΔS10 estimated to be -133 ± 11 J/K·mol, ΔH10 = -69 ± 3 kJ/mol and ΔHf0(Cl2O2) = 136 ± 3 kJ/mol.
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• 68
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ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Since 1926 investigations of the Dushman reaction have relied mainly upon “constant-rate” measurements, usually by instrumental methods. Since about that time, the confusion surrounding this venerable reaction has been growing. In part, the confusion arises because the reaction involves reactive intermediate species that have not been studied directly - and may never be. Alternative detailed mechanisms have been assumed with little restraint. One of these, which is built around H2I2O3, has been explored by computer with promising results. The mechanism seems capable of reducing the confusion now attending the Dushman reaction and others related to it.