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• Atomic, Molecular and Optical Physics  (2,271)
• Physical Chemistry  (1,466)
• 1990-1994  (2,738)
• 1970-1974  (697)
• 1965-1969  (302)
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• 101
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: The UV absorption spectrum and kinetics of CH2I and CH2IO2 radicals have been studied in the gasphase at 295 K using a pulse radiolysis UV absorption spectroscopic technique. UV absorption spectra of CH2I and CH2IO2 radicals were quantified in the range 220-400 nm. The spectrum of CH2I has absorption maxima at 280 nm and 337.5 nm. The absorption cross-section for the CH2I radicals at 337.5 nm was (4.1 ± 0.9) × 10-18 cm2 molecule-1. The UV spectrum of CH2IO2 radicals is broad. The absorption cross-section at 370 nm was (2.1 ± 0.5) × 10-18 cm2 molecule-1. The rate constant for the self reaction of CH2I radicals, k = 4 × 10-11 cm3 molecule-1 s-1 at 1000 mbar total pressure of SF6, was derived by kinetic modelling of experimental absorbance transients. The observed self-reaction rate constant for CH2IO2 radicals was estimated also by modelling to k = 9 × 10-11 cm3 molecule-1 s-1. As part of this work a rate constant of (2.0 ± 0.3) × 10-10 cm3 molecule-1 s-1 was measured for the reaction of F atoms with CH3I. The branching ratios of this reaction for abstraction of an I atom and a H atom were determined to (64 ± 6)% and (36 ± 6)%, respectively. © 1994 John Wiley & Sons, Inc.
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• 102
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: Salt effects on the oxidation of the iron(II) complexes Fe(CN)4(bpy)2-, cis-(CN)2(bpy)2 and Fe(bpy)32+ by S2O82- as well as on the reaction Fe2+ + Co(NH3)5Cl2+ have been studied in concentrated electrolyte solutions at 298.2 K. We have gone from anion-anion to cation-cation reaction with the intermediate cases of anion-neutral and cation-anion reactions. Results show that the main cause of the kinetic salt effects observed is the interaction between supporting electrolytes and the solvent. © 1994 John Wiley & Sons, Inc.
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• 103
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
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• 104
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 model is presented to describe the high temperature (1800 K 〈 T 〈 3000 K) surface oxidation of particulate boron in a hydrocarbon combustion environment. The model includes a homogeneous gas-phase B/O/H/C oxidation mechanism consisting of 19 chemical species and 58 forward and reverse elementary reactions, multi-component gas-phase diffusion, and a heterogeneous surface oxidation mechanism consisting of ‘elementary’ adsorption and desorption reaction steps. Thermochemical and kinetic parameters for the surface reactions are estimated from available experimental data and/or elementary transition state arguments. The kinetic processes are treated using a generalized kinetics code, with embedded sensitivity analysis, for the combustion of a one-dimensional (particle radius), spherical particle. Model results are presented for the oxidation of a 200 μm boron particle in a JP-4/air mixture at ambient temperatures of 1400 K and 2000 K. These results include temperature and gas-phase species profiles as a function of radial distance and particle burning rates. © 1994 John Wiley & Sons, Inc.
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• 105
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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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• 106
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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 model is proposed for performing microcanonical variational transition state theory calculations which incorporates ideas from vibrator and flexible variational transition state models. Vibrational frequencies, moments of inertia, and potential energy for the variational transition state are found by reaction path following as for the vibrator model. However, the transitional modes are treated as hindered rotors using an analytic potential and an analytic density of states, which are fit to barriers for hindered rotation determined from reaction path following. The model proposed here differs from the flexible transition state model in that the density of states for the transitional modes is analytic and transitional modes and external rotational angular momenta are uncoupled. For the H + CH3 ⇌ CH4 system, rate constants calculated with this new model are only 6-23% smaller on average from those of the flexible transition state model for values of total angular momentum which correspond to average rotational temperatures of 0-2000 K. Harmonic frequencies calculated for the transitional modes from the hindered rotor Hamiltonian are in good agreement with the exact values found by a reaction path analysis. © 1994 John Wiley & Sons, Inc.
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• 107
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
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• 108
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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 thermal decomposition reaction of gaseous 3,3,6,6-tetramethyl-1,2,4,5-tetroxane (ACDP) in the presence of n-octane was studied in the 403.2-523.2 K temperature range. This reaction yields acetone as the organic product. Under optimum conditions, first-order kinetics were observed, included when the S/V ratio of the Pyrex reaction vessel was increased by a nearly six-fold factor. In the range 443.2-488.2 K the temperature dependence of the rate constants for the unimolecular reaction in conditioned vessels is given by In k1/(s-1) = (31.8 ± 2.5) - [(39.0 ± 2.5)/RT]. The value of the energy of activation in kcal/mol correspond to one O—O bond homolysis of the ACDP molecule in a stepwise biradical initiated decomposition mechanism. At the lower reaction temperatures as well in preliminary experiments participation of a surface catalyzed ACDP decomposition process could be detected. © 1994 John Wiley & Sons, Inc.
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• 109
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
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• 110
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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 yield of 16OS18O from the 18OH initiated oxidation of CS2 in 16O2 was measured by using a discharge flow reactor coupled to a chemical ionization mass spectrometer. 16OS18O is the dominant SO2 isotopomer produced with a yield of 0.90 ± 0.20 relative to 18OH loss. The errors are estimates for the uncertainty at the 95% confidence level. The implications of these results to the understanding of the CS2 oxidation mechanism are discussed. © 1994 John Wiley & Sons, Inc.This article is a US Government work and, as such, is in the public domain in the United States of America.
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• 111
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: The equations necessary for the determination of the rate constants corresponding to the opposite elementary steps for formation of the oxidant-reductant ester intermediate, as well as that corresponding to its redox decomposition, in the reduction of chromium(VI) by glutathione and other thiols at physiological pH have been deduced. It is shown that those three rate constants can be obtained with a good reproducibility. © 1994 John Wiley & Sons, Inc.
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• 112
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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 role of mechanistic steps, diffusion, and their interrelation is explored in a steady-state premixed laminar CO + H2 + O2 flame using a numerical model. Sensitivity coefficients and Green's functions calculated for this system offer systematic characterization of the role of diffusion and exothermicity in carbon monoxide oxidation kinetics. The results reveal that the uncertainties in transport parameters are as important to the model predictions as those in the kinetic steps. The rate controlling steps of the CO + H2 + O2 reaction are found to be different for adiabatic and nonadiabatic premixed flames, and also for systems with and without transport. In particular, the reactions of the hydroperoxyl radical with hydrogen, oxygen, and hydroxyl radicals are found to be important at all temperatures in the fuel lean (40 torr) adiabatic flame studied here. The diffusive mixing of chemical species from the low and the high temperature portions of the flame and the larger heats of reaction associated with the hydroperoxyl radicals are found to be responsible for the increased importance of these reactions. © 1994 John Wiley & Sons, Inc.
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• 113
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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 oxidation kinetics of ethanol with 3,4-lutindine chromium(VI) peroxide (LCP) were investigated by monitoring the absorbance change at 565 nm in dichloromethane solution. The reaction had a first-order dependence on oxidant and a fractional (one half) dependence on reactant. The stoichiometric ratio between LCP and ethanol was 1 : 2. The activation parameters were determined from temperature dependence of the reaction rate. It was found that the cleavage of the peroxide groups of LCP is primarily responsible for the oxidant of ethanol to acetaldehyde. Based on the kinetic results obtained (including deuterium isotope effect) a plausible mechanism is proposed. © 1994 John Wiley & Sons, Inc.
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• 114
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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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• 115
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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: Time-resolved studies of silylene, SiH2, generated by laser-flash photolysis of phenylsilane, have been employed to obtain rate constants for its bimolecular reactions with C2H2 and C2D2. The reactions have been studied in the gas-phase, in the pressure range 1-100 torr (with SF6 bath gas) at five temperatures in the range 291-613 K.Reaction with C2H2 is pressure dependent, consistent with a third body assisted association reaction. However the lack of a simple fit to RRKM calculated values suggests a more complex process with another reaction channel. Reaction with C2D2 is faster than with C2H2, showing a pressure dependent isotope effect. The data are consistent with a rapid isotopic scrambling mechanism. Further RRKM modeling of a three-channel decomposition mechanism for the suggested silirene adduct (intermediate) provides a semi-quantitative fit to the data. Rate constants extracted from the modeling are shown to be consistent with a mechanism leading to formation of both ethynylsilane and vinylsilylene, as previously proposed by O'Neal, Ring et al. from higher temperature studies. An enthalpy surface is shown to be consistent with this mechanism. © 1994 John Wiley & Sons, Inc.
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• 116
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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: Reactions of Cu2 with several small molecules have been studied in the gas phase, under thermalized conditions at room temperature, in a fast-flow reactor. They fall into one of two categories. Cu2 does not react with O2, N2O, N2, H2, and CH4 at pressures up to 6 torr. This implies bimolecular rate constants of less than 5 × 10-15 cm3 s-1 at 6 torr He. Cu2 reacts with CO, NH3, C2H4, and C3H6 in a manner characteristic of association reactions. Second-order rate constants for all four of these reagents are dependent on total pressure. The reactions with CO, NH3, and C2H4 are in their low pressure limit at up to 6 torr He buffer gas pressure. The reaction with C3H6 begins to show fall-off behavior at pressures above 3 torr. Limiting low-pressure, third-order rate constants are 0.66 ± 0.10, 8.8 ± 1.2, 9.3 ± 1.4, and 85 ± 15 × 10-30 cm6 s-1 in He for CO, NH3, C2H4, and C3H6, respectively. Modeling studies of these rate constants imply that the association complexes are bound by at least 20 kcal mol-1 in the case of C2H4 and C3H6 and at least 25 kcal mol-1 in the other cases. The implications of these results for Cu-ligand bonding are developed in comparison with existing work on the interactions of these ligands with Cu atoms, larger clusters, and surfaces. © 1994 John Wiley & Sons, Inc.
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• 117
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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: GaAs (100) wafers were etched in mixtures of hydrogen atoms and methyl radicals. The atoms were formed in a remote hydrogen plasma, and a fraction of these were converted into methyl radicals by introducing methane into the flow system upstream from the semiconductor surface. The flux of hydrogen atoms into the reaction chamber was determined by isothermal calorimetry. The methyl radical flux passing over the substrate was then calculated using previously determined rate parameters for the reaction between atomic hydrogen and methane, and a simple modeling program. The GaAs etch rates were about an order of magnitude faster when methyl radicals were present in the hydrogen atom stream, and were found to follow a first-order dependence on the partial pressure of methyl radicals. Absolute rate constants were determined and an Arrhenius activation energy of 1.2 kcal mol-1 was calculated. The values of k and Ea are consistent with a diffusion-controlled process. SEM photographs of the surface revealed small crystallographic features that made the surface appear very rough. XPS analysis indicated that these surfaces were arsenic deficient. A mechanism is proposed for the etching of GaAs by a combination of methyl radicals and hydrogen atoms. © 1994 John Wiley & Sons, Inc.
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• 118
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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: Multiphoton decomposition of 1-bromo 2-fluoroethane (CH2BrCH2F, BFE) with a two-color CO2 infrared laser is reported as a function of number of laser pulses. For single color irradiation at a wavelength chosen to excite BFE, the decomposition product, vinyl fluoride, which accumulates during the many-pulse MPD experiment, is found to deactivate BFE decomposition. When a second laser, tuned to a vinyl fluoride absorption is introduced, coincident with the first, the vinyl fluoride is found to activate further BFE decomposition. These results are accounted for in terms of a pressure-dependent model. Changes in model parameters, upon addition of the second laser, are shown to be consistent with interpretations in terms of collision-dependent reaction schemes. © 1994 John Wiley & Sons, Inc.
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• 119
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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 pulsed CO2 laser-induced decompositions of propan-2-ol, butan-2-ol, pentan-2-ol, pentan-3-ol, and hexan-2-ol in the gas phase have been investigated. Like ethanol which we examined previously [1] the absorption cross section of propan-2-ol for pulsed 9R14 radiation increases with pressure at low pressures, an effect attributed to rotational hole-filling. In contrast the absorption cross section of butan-2-ol (10R24) has only a small pressure dependence and those of pentan-2-ol (9R26), pentan-3-ol (10R14), and hexan-2-ol (9P20) show little or no variation with pressure in the range 0.1-5.0 torr.Decomposition products have been investigated at low pressure where the excitation of the alkanols was essentially collision free. The observed products for all the alkanols can be rationalized on the basis of primary dehydration and C—C fission channels, with minor contributions from other molecular eliminations. © 1994 John Wiley & Sons, Inc.
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• 120
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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: Bond dissociation energies are frequently derived from values of the high pressure activation energy for bond scission reactions. The value derived depends on the transition state structure chosen for the reaction. We consider several models of the transition state and show that the variation in derived BDE values can be quite substantial, 3 to 6 kcal/mol at the high temperatures of pyrolysis kinetics. Application of the restricted Gorin model of the transition state results in BDE values in good agreement with current thermochemistry, while the other models tested result in lower to much lower values. © 1994 John Wiley & Sons, Inc.
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• 121
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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 yields of CO2 and CO formed from the gas-phase photolysis at 222 nm of very low pressures of formic acid where the monomer predominates have been determined using FTIR spectroscopy. The observed ratio of CO2/CO approaches unity as the formic acid pressure approaches zero. Previous studies have shown that the quantum yield for HCOOH + hv → OH + HCO (or H + CO) is 0.70 at 298 K. The present experimental results indicate that the ratio of the quantum yields of the possible molecular photolysis channels forming H2 + CO2 (φ1b) and H2O + CO (φ1c) is ca. 1. Including this result in an analysis of previously reported quantum yields of CO and CO2 determined at higher pressures of formic acid, where both monomer and dimer contribute significantly to the products, indicates that φ1b = φ1c = 0. © 1994 John Wiley & Sons, Inc.
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• 122
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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: As in our previous studies, 0(3P), generated by titration with NO of microwave discharged N2 (He carrier), was mixed with B10H14 vapor (Ar carrier) in a flow-tube reactor. Levels of product OH were determined via LIF on an absolute basis, for dwell times 4 to 18 ms. The system was calibrated with C2H6, run under identical conditions. The reactants comprised approximately 1% of the flowing mixture. OH production is ≈62 greater from B10H14 than from B5H9 (under similar conditions but at somewhat lower temperature). FTIR analyses of a solid product that condensed downstream on cold surfaces showed the presence of —B—O—H⃜O—B— hydrogen bonds and matched (but not perfectly) the calculated frequencies of HB(OH)2. © 1994 John Wiley & Sons, Inc.
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• 123
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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: Structure-reactivity correlations are developed and used to test a biradical mechanism for gas-phase thermal Diels-Alder reactions of cyclohexa-1,3-diene with substituted ethenes and reverse reactions. © 1994 John Wiley & Sons, Inc.
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• 124
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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: Complex dynamical behavior has been observed in the oxidation of hydroxylamine by bromate in acidic sulfate medium. The reaction shows clock type kinetics in closed conditions and an aperiodic oscillations if gaseous products are removed from the system with a constant flow-rate. The reduction kinetics of bromate ions with excess hydroxylamine has been studied in the presence of allyl alcohol. The observed pseudo-first-order rate constant kobs has been found to follow the expression \documentclass{article}\pagestyle{empty}\begin{document}$$k_{{\rm obs}} = \frac{{kK_1 \left[{{\rm H}^ +} \right]\left[{{\rm hydroxylamine}} \right]}}{{\left({1 + {\rm K}_{\rm 1} \left[{{\rm H}^ +} \right]} \right){\rm K}_{\rm 2}}}$$\end{document} where [hydroxylamine] is total initial hydroxylamine concentration, K1 = 0.5 M-1, K2 = 106 M-1, and k = 2.57 × 103 M-1 s-1 at 298.15 K and I = 2.0 M.The rate constant for the bromine oxidation of hydroxylamine in sulfuric aqueous solution has been determined. © 1994 John Wiley & Sons, Inc.
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• 125
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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 coefficient for the reaction has been determined in mixtures of nitric acid (HNO3) and argon in incident shock wave experiments. Quantitative OH time-histories were obtained by cw narrow-linewidth uv laser absorption of the R1(5) line of the A2 σ+ ← X2 Πi (0,0) transition at 32606.56 cm-1 (vacuum). The experiments were conducted over the temperature range 1050-2380 K and the pressure range 0.18-0.60 atm. The second-order rate coefficient was determined to be \documentclass{article}\pagestyle{empty}\begin{document}$$k_1 = 9.40 \times 10^{- 5} T^{4.77} \exp \left({{{+ 4570} \mathord{\left/ {\vphantom {{+ 4570} {T\left[{\rm K} \right]}}} \right. \kern-\nulldelimiterspace} {T\left[{\rm K} \right]}}} \right)\left[{{\rm cm}^{\rm 3} {\rm mol}^{- 1} {\rm s}^{- 1}} \right]$$\end{document} with overall uncertainties of +11%, -16% at high temperatures and +25%, -22% at low temperatures. By incorporating data from previous investigations in the temperature range 298-578 K, the following expression is determined for the temperature range 298-2380 K \documentclass{article}\pagestyle{empty}\begin{document}$$k_1 = 3.57 \times 10^4 T^{2.40} \exp \left({{{+ 1063} \mathord{\left/ {\vphantom {{+ 1063} {T\left[{\rm K} \right]}}} \right. \kern-\nulldelimiterspace} {T\left[{\rm K} \right]}}} \right)\left[{{\rm cm}^{\rm 3} {\rm mol}^{- 1} {\rm s}^{- 1}} \right].$$\end{document} © 1994 John Wiley & Sons, Inc.
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• 126
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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 acid and alkaline hydrolysis of monoflorophosphorous acid has been studied by P-31 NMR and static pH titration over a wide temperature range. The acid catalyzed hydrolysis has a rate constant at 25°C equal to 0.35 dm3 mol-1 s-1 and an activation energy of 53 kJ while the alkaline hydrolysis has a rate constant of 4.6 dm3 mol-1 s-1 and an activation energy of 42 kJ. When the hydrogen in this compound is replaced by either fluorine or a hydroxyl group, the rates of reaction decrease by two orders of magnitude. © 1994 John Wiley & Sons, Inc.
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• 127
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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: Experimental and theoretical investigations of bistability occurring in the nitric acid-hydroxylamine CSTR system are presented. Features of the stationary concentration vs. inlet concentration diagram and some mechanistic implications are discussed. © 1994 John Wiley & Sons, Inc.
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• 128
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New York, NY : Wiley-Blackwell
International Journal of Chemical Kinetics 26 (1994), S. 1013-1021
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Kinetic data on the esterification of succinic anhydride with methanol catalyzed by sulfuric acid have been obtained using a stirred batch reactor. In addition to get a precise ascertainment of the parameters the esterification of monomethyl succinate with methanol has been studied separately. Several experiments have been carried out with different initial molar ratios and different amounts of sulfuric acid at various temperatures. The conversion to dimethyl succinate at 30-65°C follows a first-order rate expression with respect to each component. A theoretical rate equation is derived by the following reaction mechanism: (1) succinic anhydride is protonated by sulfuric acid to form a reaction intermediate, (2) irreversible esterification to monomethyl succinate, (3) protonation of the monoester, and (4) the esterification to dimethyl succinate proceeds reversibly. The resultant kinetic equation fitted the experimental data quite well and is given by the expression: \documentclass{article}\pagestyle{empty}\begin{document}$$\frac{{dc_{{\rm CH}_{\rm 3} {\rm OH}}}}{{dt}} = c_{{\rm H}_2 {\rm SO}_4} \left[{- 4.344*10^8 e^{- 65239/RT} c_{{\rm C}_4 {\rm H}_{\rm 4} {\rm O}_3 {\rm C}_{{\rm CH}_{\rm 3} {\rm OH}}} {\rm - 2}{\rm .457*10}^{\rm 6} e^{- 57732/RT} c_{{\rm C}_{\rm 5} {\rm H}_{\rm 8} {\rm O}_{\rm 4}} c_{{\rm CH}_3 {\rm OH}} + 229e^{- 34361/{\rm RT}} c_{{\rm C}_6 {\rm H}_{{\rm 10}} {\rm O}_{\rm 4} {\rm C}_{{\rm H}_{\rm 2} {\rm O}}}} \right]$$\end{document} © 1994 John Wiley & Sons, Inc. © 1994 John Wiley & Sons, Inc.
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• 129
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New York, NY : Wiley-Blackwell
International Journal of Chemical Kinetics 26 (1994), S. 1063-1074
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The OH- ion catalyzed hydrolysis of AOT and sodium mono-methyl succinate in aqueous and aquo-dioxane media has been studied. The second-order rate constant for the former has been found to be nearly ten times slower than that of the latter. At AOT concentrations above CMC, the rate constants become insensitive to the concentration in the studied range of temperature, 25°C-40°C. The activation parameters for the kinetic process have been found to be reasonable, negative entropy of activation has supported a stable transition state complex. A good enthalpy-entropy compensation of the kinetic process has been found both for AOT and sodium monomethyl succinate in aqueous and aquo-dioxane media supporting similar nature of the transition state complexes in the hydrolytic reactions. The enthalpies of hydrolysis of AOT and the half ester of succinic acid in aqueous and aquo-dioxane media have been also reported. © 1994 John Wiley & Sons, Inc.
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• 130
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New York, NY : Wiley-Blackwell
International Journal of Chemical Kinetics 26 (1994), S. 1105-1119
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Kinetics of manganese(III) oxidation of L-arginine has been studied in the presence of pyrophosphate and acetate ions in acidic media at 328 K and 323 K, respectively. The nature of the oxidizing species formed in manganese(III) solutions was determined by spectrophotometric and redox potential measurements. The reaction shows a first-order dependence on [manganese(III) pyrophosphate] in the pyrophosphate medium, pH 2-3, and a half-order on [manganese(III) acetate] in HOAc-acetate medium. In both media, the kinetic order is one with respect to [arginine]. The dependencies of the rate on the reduction product, manganese(II), concentration are zero- and inverse first-orders in acetate and pyrophosphate media, respectively. Effects of varying dielectric constant of the medium and of added anions such as acetate, pyrophosphate, fluoride, chloride, and perchlorate have been investigated, in both media. There is evidence for the existence of free radicals as transient species. Activation parameters have been evaluated using the Arrhenius and Eyring plots. Mechanisms consistent with the observed kinetic data have been proposed and discussed. Kinetic data for the oxidations of some α-amino acids by manganese(III) species of different forms are summarized and compared. © 1994 John Wiley & Sons, Inc.
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• 131
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International Journal of Chemical Kinetics 26 (1994), S. 1135-1141
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Nitrogenated compounds react with hypochlorous acid yielding N-chloro compounds. In principle, α-amino acids chlorination may take place on the oxygen of the carboxylic group or on the nitrogen of the amino group. In this framework, we discuss the different reactivities of nitrogen and oxygen towards chlorine, and come to the conclusion that the nitrogen is the preferred reaction site in α-amino acids chlorination. © 1994 John Wiley & Sons, Inc.
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• 132
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International Journal of Chemical Kinetics 26 (1994), S. 1167-1178
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: With a view to clarifying analogies and differences between the mechanisms involved in the nitrosation of amino acids and secondary amines, we studied the kinetics of the nitrosation of five imino acids (azetidine-2-carboxylic acid, pyrrolidine-2-carboxylic acid, piperidine-2-carboxylic acid, piperidine-3-carboxylic acid, and piperidine-4-carboxylic acid) and of the ethyl esters of three of them. Reaction kinetics were determined by the initial rate method, by spectrophotometric monitoring of the concentration of nitroso amino acid formed. The presence of the —COO- group in the amino acids opens a new mechanistic route for the nitrosation of the secondary amino group: a nitrosyl carboxylate formed initially acts as an internal nitrosating agent, resulting in intramolecular migration of —N = O from the carboxylate group to the secondary amino group. The observed order of the α-, β-, and γ-amino acids as regards the ease of N-nitrosation by this route is explained in terms of the relative energies of (a) the equatorial and axial orientations of the Cring—Ccarboxyl bond, and (b) the chair and boat forms of the piperidine ring. © 1994 John Wiley & Sons, Inc.
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• 133
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International Journal of Chemical Kinetics 26 (1994), S. 1179-1184
ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Nanosecond laser flash photolysis (λ = 355 nm) of an aqueous solution of 3-chloro-3-p-chlorophenyldiazirine in isooctane produces a transient absorption at 310 nm due to the formation of the carbene. In the presence of 2-vinylpyridine, a second transient with a broad absorption band peaking at 520 nm grows in. This absorption is attributed to 2-vinylpyridinium ylide. The ylide decays with a lifetime equal to 33 µs at 25°C independent of the concentration of 2-vinylpyridine. As the ylide decays, there is a concomitant growth of an absorption at 330 nm, attributed to the formation of inodolizine. The activation parameters for the 1,5-dipolar cyclization of the ylide to indolizine were determined; Ea = 12.1 kcal mol-1 and log A = 13.4. © 1994 John Wiley & Sons, Inc.
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• 134
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Notes: The absolute rate constants for the intermolecular hydrogen abstraction reactions of secondary hydrogens by secondary alkylperoxy radicals in hexadecane autoxidation, k3, have been determined in the temperature range of 120-190°C using the stirred flow reactor technique. Absolute rate constants determined in this study for hexadecane are in good agreement with those determined for other hydrocarbons in liquid phase, on a per hydrogen basis, at lower temperatures. Arrhenius parameters for k3/H derived from this study are A = 108.6 M-1 s-1 and Ea = 16.0 kcal/mol. The values of these parameters provide experimental confirmation for previous estimates made from both lower temperature reactions in the liquid phase and higher temperature reactions in the gas phase. © 1994 John Wiley & Sons, Inc.
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• 135
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• 136
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• 137
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Notes: The kinetics of the gas-phase reactions of O3 with a series of alkenes and two α,β-unsaturated ketones have been investigated at atmospheric pressure (ca. 740 torr) of air and 296 ± 2 K, using a relative rate method in the presence of sufficient cyclohexane to scavenge OH radicals generated in these reactions. Combined with our previous relative rate measurements (Int. J. Chem. Kinet., 24, 803 (1992)), the rate constants obtained relative to k(O3 + propene) = 1.00 were: 3-penten-2-one, 3.62 ± 0.16; 2-cyclohexen-1-one, 〈0.19; bicyclo[2.2.2]-2-octene, 7.44 ± 0.48; 1,3-cycloheptadiene, 16.1 ± 1.1; cycloheptene, 23.7 ± 1.6; 1,3-cyclohexadiene, 134 ± 13; bicyclo[2.2.1]-2-heptene, 170 ± 16; and bicyclo[2.2.1]-2,5-heptadiene, 390 ± 36. The resulting rate constants then lead to a self-consistent set of room temperature data for the reactions of O3 with these alkenes and α,β-unsaturated ketones. These rate constants are compared with the literature data, and the effects of ring size discussed. © 1994 John Wiley & Sons, Inc.
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• 138
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Notes: An improved method has been used to synthesize perfluoroazo-2-propane. Pyrolysis over the temperature range 450-514 K in a static system has been shown to be a homogeneous, first-order process. No pressure dependence was observed in the presence of excess inert gas (SF6). The only products were nitrogen and perfluoro-2,3-dimethylbutane. The rate constant (k) for the decomposition process is given by: \documentclass{article}\pagestyle{empty}\begin{document}$$\log \left({{k \mathord{\left/{\vphantom {k s}} \right. \kern-\nulldelimiterspace} s}^{- 1}} \right) = 16.7 \pm 0.2 - {{\left({9856 \pm 109} \right)} \mathord{\left/{\vphantom {{\left({9856 \pm 109} \right)} T}} \right. \kern-\nulldelimiterspace} T}$$\end{document} These results lead to a straightforward mechanism for the decomposition process The results are compared with those for other azo compounds. © 1994 John Wiley & Sons, Inc.
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• 139
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Notes: The association reactions of atomic nickel with ethene and fully deuterated ethene in carbon dioxide buffer gas at 295 K have been investigated in the pressure range 5-100 torr, using a laser photolysis-laser fluorescence technique. By comparison with results of ab initio quantum chemistry calculations for the complex Ni[C2H4], the data are shown to be consistent with reaction on both ground and excited state potential energy surfaces. A simple rate equations treatment is described which shows the form of the pressure dependence of the second-order recombination rate coefficient in this case. Under conditions which are expected to hold for the Ni + C2H4 (C2D4) reaction, the pressure dependence has the standard Lindemann-Hinshelwood form, with the limiting high pressure rate constant given by an apparent value which reflects the degree to which the participating electronic states are coupled by nonadiabatic transitions. The limiting high pressure behavior of the recombination rate coefficient for Ni + C2H4 is not strongly affected by deuterium isotope substitution. However, the effect on the low pressure rate constant is large and consistent with RRKM unimolecular reaction theory. This validates the use of RRKM calculations for estimating the binding energy of the complex from kinetic data. The binding energy of Ni[C2H4] is estimated to be 35.2 ± 4.2 kcal mol-1. © 1994 John Wiley & Sons, Inc.
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• 140
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Notes: Rate constants are calculated for CH3 (+ Ar) ⇄ CH2 + H (+ Ar) at the limiting low-pressure, the limiting high-pressure, as well as the intermediate fall-off ranges. The results show that published experimental rate constants for methyl dissociation correspond to the fall-off region close to the low-pressure limit. At the low-pressure limit the activation energy is less than the bond dissociation energy, in agreement with experimental results. Forward and backward rate coefficients at the high-pressure limit are compared with other theoretical calculations. More theoretical and experimental work is necessary to understand the reverse reaction and its competing reactions, as well as the decomposition channel leading to CH + H2. © 1994 John Wiley & Sons, Inc.
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• 141
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Notes: The photolysis of mixtures of acetone and propylene at 308 nm has been studied kinetically from approximately 300 K to 580 K. Rate constants were calculated for the reactions at total pressures ranging from 110 torr to 750 torr and for [C3H6]/[(CH3)2CO] ratios in the range 0.03 to 3.3. No dependence of the rate constants on total pressure or on this concentration ratio could be detected within this range of conditions. The temperature dependence of the rate constants is given by \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{l} k_{\rm 1} = 7.2 \times 10^7 \left({\pm 22\%} \right)\exp \left({{{- 3260 \pm 40} \mathord{\left/ {\vphantom {{- 3260 \pm 40} T}} \right. \kern-\nulldelimiterspace} T}} \right){\rm M}^{- 1} {\rm s}^{- 1} \\ k_{\rm 2} = 1.6 \times 10^8 \left({\pm 32\%} \right)\exp \left({{{- 4440 \pm 90} \mathord{\left/{\vphantom {{- 4440 \pm 90} T}} \right. \kern-\nulldelimiterspace} T}} \right){\rm M}^{- 1} {\rm s}^{- 1} \\ \end{array}$$\end{document} © 1994 John Wiley & Sons, Inc.
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• 142
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Notes: An extension of the dimensionless treatment of Troe is developed for fitting falloff data from unimolecular and recombination reactions. This method using dimensionless parametrizations derived from accurate numerical solutions of the master equation for system with any type of activated complex and energy transfer probability distribution, is as easily implemented as Troe's method, and allows global fitting of an entire set of pressure- and temperature-dependent rate coefficients. © 1994 John Wiley & Sons, Inc.
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• 143
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Notes: The infrared multiphoton decomposition (IR MPD) of t-butyl chloride-d9 as a function of pressure and fluence is reported. The major decomposition route was molecular elimination of DCl in accord with earlier pyrolysis studies. The effect of added gases (2-methyl propene-d8, DCl and 2-methyl propene-h8) on the MPD is presented. This study is a further example of the utility of a new method of analysis of MPD experiments. © 1994 John Wiley & Sons, Inc.
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• 144
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Notes: A study of the reaction initiated by the thermal decomposition of di-t-butyl peroxide (DTBP) in the presence of (CH3)2C=CH2 (B) at 391-444 K has yielded kinetic data on a number of reactions involving CH3 (M·), (CH3)2CCH2CH3 (MB·) and (CH3)2ĊCH2C(CH3)2CH2CH3 (MBB·) radicals.The cross-combination ratio for M· and MB· radicals, rate constants for the addition to B of M· and MB· radicals relative to those for their recombination reactions, and rate constants for the decomposition of DTBP, have been determined. The values are, respectively, \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{*{20}c} {\phi \left({{\rm M} \cdot {\rm, MB} \cdot} \right) = \left({2.3 \pm 0.2} \right)} \\ {\log \left({{{k_2} \mathord{\left/ {\vphantom {{k_2} {k_5^{1/2}}}} \right. \kern-\nulldelimiterspace} {k_5^{1/2}}}} \right) = \left({3.18 \pm 0.32} \right) - {{\left({28.0 \pm 1.3} \right)} \mathord{\left/ {\vphantom {{\left({28.0 \pm 1.3} \right)} \theta}} \right. \kern-\nulldelimiterspace} \theta}} \\ {\log \left({{{k_9} \mathord{\left/ {\vphantom {{k_9} {k_{15}^{1/2}}}} \right. \kern-\nulldelimiterspace} {k_{15}^{1/2}}}} \right) = \left({2.2 \pm 0.9} \right) - {{\left({24.4 \pm 2.5} \right)} \mathord{\left/ {\vphantom {{\left({24.4 \pm 2.5} \right)} \theta}} \right. \kern-\nulldelimiterspace} \theta}} \\ {\log \left({k_0} \right) = \left({15.57 \pm 0.23} \right) - {{\left({156.3 \pm 2.2} \right)} \mathord{\left/ {\vphantom {{\left({156.3 \pm 2.2} \right)} \theta}} \right. \kern-\nulldelimiterspace} \theta}} \\\end{array}$$\end{document} where θ = RT ln 10 and the units are dm3/2 mol-1/2 s-1/2 for k2/k51/2 and k9/k151/2, s-1 for k0, and kJ mol-1 for E.Various disproportionation-combination ratios involving M·, MB·, and MBB· radicals have been evaluated. The values obtained are: Δ1(M·, MB·) = 0.79 ± 0.35, Δ1(MB·, MB·) = 3.0 ± 1.0, Δ1(MBB·, MB·) = 0.7 ± 0.4, Δ1(M·, MBB·) = 4.1 ± 1.0, Δ1(MB·, MBB·) = 6.2 ± 1.4, and Δ1(MBB·, MBB·) = 3.9 ± 2.3, where Δ1 refers to H-abstraction from the CH3 group adjacent to the center of the second radical, yielding a 1-olefin. © 1994 John Wiley & Sons, Inc.
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• 145
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Topics: Chemistry and Pharmacology
Notes: This article describes a dynamic model for formation and stability of CO2-hydrate on the interface of liquid CO2(LCO2) and ocean water at large depths. Experimental results indicate that a thin film of hydrate naturally forms on the interfaces between LCO2 and water, and inhibits diffusion between the two phases. Experiments further shows that the flux of CO2 through the hydrate film is dependent of the CO2-concentration in the ambient sea water. The model proposed here explains these phenomena by introducing four major mechanisms; diffusion of water to the LCO2-phase, formation of hydrate in the LCO2-hydrate interface, decay of hydrate in the water-hydrate interface, and diffusion of CO2 through the water phase. The model explains the CO2 flux not by diffusion through the hydrate film, but suggest a mechanism of continuous hydrate formation and decay. The overall effect is a “moving,” pseudo-steady-state hydrate film due to transport of CO2 through the film. The film velocity is dependent of liquid-liquid diffusivity parameters and reaction constant, and lacking experimental values of these parameters, an order-of-magnitude analysis is done by fitting the model to experimentally obtained data for the overall film velocity. The motivation for this work is to elucidate options for CO2 depositions in deep oceans, of which liquid CO2 sequestration is believed to be one of the most feasible. Spreading of CO2 from a liquid CO2-lake and associated lowering of pH in the ecosystem surrounding the lake is of large concern. The work presented here concludes that diffusion of CO2 in the ocean is largely reduced by the hydrate film and suggests that hydrate formation may alleviate some of the environmental concerns regarding deep ocean sequestration of liquid CO2. © 1994 John Wiley & Sons, Inc.
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• 146
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Notes: The reactions of 1,2-dichloroethane with 2-(ethylamino)ethanol or diethylamine have been investigated in several solvents from 51 to 80°C. A reaction mechanism has been proposed where 1,2-dichloroethane reacts with the secondary amines in both bimolecular substitution (SN 2) and elimination (E2) reactions; the substitution product is rapidly converted in an aziridinium ion and undergoes a consecutive reaction with the starting amine to give a tetrasubstituted ethylenediamine. The rate constants as well as the activation energies of these reactions have been determined. © 1994 John Wiley & Sons, Inc.
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• 148
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Notes: The kinetics of hydrogen peroxide decomposition has been investigated in the presence of Wofatit KPS (4% DVB, 40-80 μm) resin in the form of mono (mea), di (dea), triethanolamine (tea), ethylenediamine (eda), and N,N′-diethylethylenediamine (deeda)- Mn(II) complexes. The rate constant k (per g dry resin) was evaluated over the temperature range 25-40°C. The reaction was first-order with respect to [H2O2]. The rate constant, k, with the three ethanolamines decreased in the following order mea 〉 dea 〉 tea which is the same order of basicity. Also, k value with deeda is lower than eda as a result of steric hindrance. The peroxo metal complex which formed at the beginning of the reaction, was found to contain the catalytic active species. The rate of reaction was proportional to [Mn-complex], [H2O2] and [H+]-1. The activation parameters were calculated and a probable reaction mechanism is proposed. © 1994 John Wiley & Sons, Inc.
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• 149
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Notes: The kinetics of the title reactions were investigated in a discharge flow tube by using laser magnetic resonance detection of HO2. The upper limits for the bimolecular rate constants for the reactions of HO2 with H2S (k1), CH3SH (k2), and CH3SCH3 (k3) are 〈3 × 10-15, 〈4 × 10-15, and 〈5 × 10-15 cm3 molecule-1 s-1, respectively, at 298 K. Our upper limit for k1 is three orders of magnitude lower than the previously reported value.Measurements at higher temperatures also yield similar upper limits. Our results suggest that HO2 is not an important oxidant for these reduced compounds in the atmosphere. © 1994 John Wiley & Sons, Inc.
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Notes: Rate coefficients for the reaction of NO3 with dimethyl ether, diethyl ether, di-n-propyl ether, and methyl t-butyl ether (MTBE) have been determined. Absolute rates were measured at temperatures between 258 and 373 K using the fast flow-discharge technique. Relative rate experiments were also made at 295 K in a reactor equipped with White optics and using FTIR spectroscopy to follow the reactions. The measured rate coefficients (in units of 10-15 cm3 molecule-1 s-1) at 295 K are: 0.26 ± 0.11, 2.80 ± 0.23, 6.49 ± 0.65, and 0.64 ± 0.06 for dimethyl ether, diethyl ether, di-n-propyl ether, and methyl t-butyl ether, respectively. The corresponding activation energies are 21.0 ± 5.0, 17.2 ± 4.0, 15.5 ± 2.1, and 20.1 ± 1.7 kJ mole-1. The error limits correspond to the 95%-confidence interval. © 1994 John Wiley & Sons, Inc.
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• 151
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Notes: The gas-phase thermal decomposition rate of peroxy-n-butyryl nitrate (n-C3H7C(O)OONO2, PnBN) has been measured at ambient temperature (296 K) and 1 atm of air relative to that of peroxyacetyl nitrate (CH3C(O)OONO2, PAN) using mixtures of PAN (14-19 ppb), PnBN (22-46 ppb), and nitric oxide (1.35-1.90 ppm). The PnBN/PAN decomposition rate ratio was 0.773 ± 0.030. This ratio, together with a literature value of 3.0 × 10-4 s-1 for the thermal decomposition rate of PAN at 296 K, yields a PnBN thermal decomposition rate of (2.32 ± 0.09) × 10-4 s-1. The results are briefly discussed by comparison with data for other peroxyacyl nitrates and with respect to the atmospheric persistence of PnBN. © 1994 John Wiley & Sons, Inc.
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• 152
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Notes: Pseudo-first-order rate constants and activation parameters have been measured for the solvolysis of 2-chloroquinoxaline in various aquo-organic mixtures using methanol, ethanol, and isopropanol as the organic solvent. Excellent linear correlations are found between lnk and the mol fraction of cosolvent and ln[H2O]. The medium effect on the rates of solvolysis is assessed by Grunwald-Winstein's mY correlationship. The estimated values of m (0.55-0.72) and the entropy of activation (148-212 J deg-1 mol-1) for the reactions are well in the range for a bimolecular aromatic substitution reactions. © 1994 John Wiley & Sons, Inc.
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• 153
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Notes: We have investigated the impact of surface reactions such as NH3 decomposition and radical adsorption on quartz flow reactor data for Thermal DeNOx using a model that accounts for surface chemistry as well as molecular transport. Our calculations support experimental observations that surface effects are not important for experiments carried out in low surface to volume quartz reactors. The reaction mechanism for Thermal DeNOx has been revised in order to reflect recent experimental results. Among the important changes are a smaller chain branching ratio for the NH2 + NO reaction and a shorter NNH lifetime than previously used in modeling. The revised mechanism has been tested against a range of experimental flow reactor data for Thermal DeNOx with reasonable results. The formation of N2O in Thermal DeNOx has been modelled and calculations show good agreement with experimental data. The important reactions in formation and destruction of N2O have been identified. Our calculations indicate that N2O is formed primarily from the reaction between NH and NO, even though the NH2 + NO2 reaction possibly contributes at lower temperatures. At higher temperatures N2O concentrations are limited by thermal dissociation of N2O and by reaction with radicals, primarily OH. © 1994 John Wiley & Sons, Inc.
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• 154
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Notes: The kinetics of the gas-phase reaction of the NO3 radical with naphthalene have been investigated at 150 torr O2 + 590 torr N2 and 600 torr O2 + 140 torr N2 at 298 ± 2 K. Relative rate measurements were carried out in reacting NO3—N2O5-naphthalene-propene-O2—N2 mixtures by longpath Fourier transform infrared absorption spectroscopy. A rate constant ratio for the reactions of O2 and NO2 with the NO3-naphthalene adduct of kO2/kNO2 〈 4 × 10-7 was obtained from the competition between O2 and NO2 for reaction with the NO3-naphthalene adduct and thermal decomposition of the adduct back to reactants. Atmospheric pressure ionization MS/MS measurements of the nitronaphthalene products of the NO3 radical-initiated reaction of naphthalene are consistent with the proposed reaction mechanism, and the atmospheric implications of the data are discussed. © 1994 John Wiley & Sons, Inc.
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• 155
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Notes: The dynamical aspects of some α-diazoketones (DZ) photolysis are investigated within the framework of statistical theories (RRKM formulation). On the whole, the results agree satisfactorily with the gas-phase experimental observations (quantum yields). In particular, the reactions DZ + hv → α-ketocarbene (KC) + N2, appear to be mainly governed by statistical behavior. The two channel isomerizations KC → ketene (KE), i.e, the Wolff Rearrangement, and KC → α,β-unsaturated ketone (ON) are also considered. It is suggested that the trapping of the α-ketocarbenes and oxirenes (OX) species would be favored under appropriate conditions (among them the irradiation wavelength and the relaxation processes involved in the reactive medium). The parametrization of the model relies on semi-empirical quantum calculations and is improved by some adjustments with experimental data. © 1994 John Wiley & Sons, Inc.
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• 156
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Notes: The multiphoton decomposition of CF3I with a pulsed CO2 laser has been studied at incident fluences of 0.6 and 1.2 J/cm2. The effect of pressure on the reaction probability for dissociation of CF3I was measured in the presence of added isobutane, Ar and CO2. In the experiments with isobutane, the CF3 radicals generated by the decomposition of excited CF3I react to yield CF3H in competition with the recombination to C2F6. The laser absorption cross section was also measured as a function of fluence at a pressure of 0.1 torr of CF3I and with 0.5-2.0 torr of added isobutane. The experimental results were modeled with a master equation in order to obtain information on the energy transferred by collisions of excited CF3I with the bath molecules. An energy dependent value of 〈ΔE〉d produces the best fit to the experimental data. Integration of the rate equations to account for the fractional product yield, [CF3I]/[C2F6], allowed for the calculation of the specific rate constant for hydrogen abstraction from isobutane by CF3 radicals. The value obtained is dependent on the total pressure and higher than expected at room temperature. From these results, an effective temperature for the reaction mixture was calculated. © 1994 John Wiley & Sons, Inc.
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• 157
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Notes: An exceptional kinetic behavior on the reactivity of β-diketones against copper(II) have been found. Some relationship between ligand basicity and unexpected enhancement on the rates of complex formation, which may be useful for predicting rate constants of similar monochelated copper(II) complexes, are established. © 1994 John Wiley & Sons, Inc.
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Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Ignition of propane has been studied in a shock tube and by computational modeling to determine the effect of methyl tert-butyl ether (MTBE) as a fuel additive. MTBE and isobutene were added in amounts up to 25% of the fuel to propane-oxygen-argon mixtures in shock tube experiments covering a range of temperatures between 1450 and 1800 K. Ignition delays were measured from chemiluminescence at 432 nm due to excited CH radicals. The temperature dependence of the ignition rates was analyzed to yield Arrhenius parameters of Ea ca. 40 kcal/mol and A ca. 109 s-1 for the overall propane reaction and Ea ca. 34 kcal/mol and A ca. 108.3 s-1 for the overall propane/MTBE reaction. Reactions involving MTBE and its decomposition products were combined with an established propane mechanism in a numerical model to describe the kinetic interaction of this additive with a typical hydrocarbon fuel. The experiments and the kinetic model both show that MTBE and isobutene retard propane ignition with nearly equal efficiency. The kinetic model demonstrates that isobutene kinetics are responsible for inhibition by both MTBE and isobutene, and the specific elementary reactions that produce this behavior are identified. © 1994 John Wiley & Sons, Inc.
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• 159
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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 nature of interaction of Co(III) complexes such as Co(III)EDTA and Co(III)NTA with transient adducts of thymine such as TOH·, T·-, and TH· formed in the gamma radiolysis of thymine were studied. The study shows that TOH radicals do not undergo electron transfer reaction with Co(III) complexes whence no radiosensitization of thymine by Co(III) complexes was observed. Electron transfer however, takes place from T·- and TH· to Co(III) complexes. A plausible mechanism of radiolysis of thymine in presence of Co(III) complexes is discussed. © 1994 John Wiley & Sons, Inc.
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• 160
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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 base hydrolysis of (αβ S)-(o-methoxy benzoato) (tetraethylenepentamine)cobalt(III) obeyed the rate law: kobs = kOH[OH-], in the range 0.05 ≤ [OH-]T, mol dm-3 ≤ 1.0, I = 1.0 mol dm-3, and 20.0-40.0°C. At 25°C, kOH = 13.4 ± 0.4 dm3 mol-1 s-1, ΔH≠ = 93 ± 2 kJ mol-1 and ΔS≠ = 90 ± 5 JK-1 mol-1. Several anions of varying charge and basicity, CH3CO2-, SO32-, SO42-, CO32-, C2O42-, CH2(CO2)22-, PO43-, and citrate3- had no effect on the rate while phthalate2-, NTA3-, EDTA4-, and DTPA5- accelerated the process via formation of the reactive ion pairs. The anionic (SDS), cationic (CTAB), and neutral (Triton X-100) micelles, however, retarded the reaction, the effect being in the order SDS〉 CTAB 〉 Triton X-100. The importance of electrostatic and hydrophobic effects of the micelles on the selective partitioning of the reactants between the micellar and bulk aqueous pseudo-phases which control the rate are discussed. © 1994 John Wiley & Sons, Inc.
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• 161
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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: Classical trajectory calculations on the methyl isocyanide molecule at energies above 25,000 cm-1 confirm that the rate of reaction to methyl cyanide is bimodal, with a very fast rate before 0.1 ps, and a slower rate from then on. We conclude that before 0.1 ps, the reacting molecules are unrandomized, but thereafter, they are essentially randomized, with decay to products being, to a good approximation, pure exponential. We estimate that the time for randomization is roughly 0.3 ps at energies near the reaction threshold of 13,500 cm-1. © 1994 John Wiley & Sons, Inc.
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• 162
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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 new flowtube reactor employing dissociative electron attachment to produce radicals and high-pressure photoionization in the mass spectrometric detection of radicals is described. The system has been applied to a study of the association reactions of CHCl2 and CCl3 with O2 in a great excess of helium at total densities below 1017 cm-3 over the temperature range 286 to 332 K. Both reactions display a strong negative temperature coefficient. The results can be parameterized in the form k0(CHCl2 + O2) = (4.3 ± 0.2) × 10-31(T/300)-6.7±0.7 cm6 s-1, k0(CCl3 + O2) = (2.7 ± 0.2) × 10-31(T/300)-8.7±1.0 cm6 s-1. © 1994 John Wiley & Sons, Inc.
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• 163
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ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: The rate constants for the reaction of C6H5 with HBr and DBr have been measured with the cavity-ring-down method in the temperature range of 297 to 523 K and 297 to 500 K, respectively. These rate constants can be effectively represented, in units of cm3/s, by \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{l} k_{{\rm HBr}} = 10^{- 10.40 \pm 0.24} \exp \left[{{{\left({- 554 \pm 208} \right)} \mathord{\left/ {\vphantom {{\left({- 554 \pm 208} \right)} T}} \right. \kern-\nulldelimiterspace} T}} \right]{\rm and} \\ k_{{\rm DBr}} = 10^{- 10.36 \pm 0.17} \exp \left[{{{\left({- 662 \pm 151} \right)} \mathord{\left/ {\vphantom {{\left({- 662 \pm 151} \right)} T}} \right. \kern-\nulldelimiterspace} T}} \right]{\rm.} \\ \end{array}$$\end{document} Both activation energies are similar and positive, contrary to those of alkyl radical reactions, all of which exhibit negative temperature dependencies. The difference, as pointed out before [1], could be accounted for by the electron-withdrawing effect of the phenyl vis-à-vis the electron-donating ability of the alkyls. © 1994 John Wiley & Sons, Inc.
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• 164
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ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: Time-resolved vibrational chemiluminescence from HF has been recorded following the production of F atoms by the pulsed laser photolysis (λ = 266 nm) of F2 in the presence of HCl, CH4, and CF3H. In the first two cases, experiments have been conducted by observing emission from HF(ν = 3) at four temperatures from 295 to 139 K. Rate constants have been determined over this range of temperature for the reactions of F atoms with HCl and CH4 and of CH3 radicals with F2, and for the relaxation of HF(ν = 3) by HCl and CH4. The reaction of F atoms with CF3H is slower than those with HCl and CH4 and measurements on the emission from HF(ν = 2) have been used to infer rate constants for reaction and relaxation only at 295 K. © 1994 John Wiley & Sons, Inc.
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• 165
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ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
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• 166
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ISSN: 0538-8066
Keywords: Chemistry ; Physical Chemistry
Source: Wiley InterScience Backfile Collection 1832-2000
Topics: Chemistry and Pharmacology
Notes: In earlier work on the room temperature oxidation of C2H2 by O atoms, two distinct sources of methylene radicals have been identified: (i) direct, primary production via channel 1b of the C2H2 + O reaction, and (ii) delayed formation via the secondary reaction 3 involving the products HCCO and H of the other primary channel 1a: Presently, it was confirmed by a detailed sensitivity analysis that the precise shapes of the resulting total methylene concentration-versus-time profiles in C2H2/O systems depend strongly on the k1a/k1b branching ratio. Along that line, the important parameter k1a/k1b was determined from relative CH2 concentration-versus-time profiles measured in a variety of C2H2/O/H systems using Discharge Flow-Molecular Beam sampling Mass Spectrometry techniques (DF-MBMS). The data analysis was carried out by deductive kinetic modelling; the method, as applied to profile shapes, is discussed at length. Via this novel, independent approach, the CH2(3B1) yield of the two-channel C2H2 + O reaction was determined to be k1b/k1 = 0.17 ± 0.08. The indicated 2σ error includes possible systematic errors due to uncertainties in the rate constants of other reactions that influence the shapes of the CH2 profiles. The present result, which translates to an HCCO yield k1a/k1 = 0.83 ± 0.08, is in excellent agreement with other recent determinations. The above mechanism, with the subsequent reactions that it initiates, also reproduces the measured absolute [C2H2], [O], and [H] profiles with an average accuracy of 5%, thus validating the consistency of the C2H2/O/H reaction model put forward here. © 1994 John Wiley & Sons, Inc.