Rate constants have been measured by the flowing afterglow technique at 300 °K for the quenching of Ar(3P2), Ar(3P0), Kr(3P2), and Xe(3P2) by a large number of small molecules. For the same reagent, the magnitudes of the cross‐sections usually increase in the series Ar(3P2), Ar(3P0), Kr(3P2), and Xe(3P2). The Ar(3P2) and Ar(3P0) data are compared to results in the literature for these states and to data for Ar(3P1) and Ar(1P1). The set of thermal quenching cross sections are used to test the correlations between the magnitudes of the cross sections and properties of the reagents as predicted by the orbiting, absorbing‐sphere, golden rule, and curve‐crossing mechanisms for quenching. The best correlation is between the cross sections and the C6 coefficient. The analysis supports the proposition that the orbiting‐controlled, curve‐crossing model is the general mechanism governing the magnitude of the thermal cross sections for quenching of the metastable states. This model explains the very large quenching cross sections of F2 and OF2 (relative to other molecules composed of first row elements) because covalent–ionic curve crossing occurs outside the conventional orbiting radius. The validity of the simple van der Waals dispersion forces as being the dominant entrance channel interaction between the excited state rare gas atoms and the reagents is discussed.

Rate constants and quenching mechanisms for the metastable states of argon, krypton, and xenon

Rate coefficients for alkyl and alkoxy radical decomposition are important in combustion, biological, and atmospheric processes. In this paper, rate constant expressions for C1C4 alkyl and alkoxy radicals decomposition via β-scission are recommended based on the reverse, exothermic reaction, the addition of a hydrogen atom or an alkyl radical to an olefin or carbonyl species with the decomposition reaction calculated using microscopic reversibility. The rate expressions have been estimated based on a wide-range study of available experimental data. Rate coefficients for hydrogen atom and alkyl radical addition to an olefin show a strong temperature curvature. In addition, it is found that there is a correlation between the activation energy for addition and (i) the type of atom undergoing addition and (ii) whether this radical adds to the internal or terminal carbon atom of the olefin. Rate coefficients for alkoxy radical decomposition show a strong correlation to the ionization potential of the alkyl radical leaving group and on the enthalpy of reaction. It is shown that the activation energy for alkyl radical addition to a carbonyl species can be estimated as a function of the alkyl radical ionization potential and enthalpy of reaction. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 250–275, 2006

Rate constant estimation for C1 to C4 alkyl and alkoxyl radical decomposition

Experiments showing that water is decomposed by the action of high-energy radiations date back to the first days of the discovery of radioactivity, a century ago. On the occasion of this anniversar...

La radiolyse de l'eau et des solutions aqueuses : historique et actualité

Organic radical ions in rigid systems

This paper is a detailed critical review of the production processes and reactions of N, N+, N+ 2, N++, and N++ 2 of relevance to Titan's atmosphere. The review includes neutral, ion-molecule, and recombination reactions. The review covers all possible active nitrogen species under Titan's atmospheric conditions, specifically N2 (A3Σ+ u), N (4 S), N (2 D), N (2 P), N+ 2, N+ (3 P), N+ (1 D), N++ 2, and N++ species, and includes a critical survey of the reactions of N, N+, N+ 2, N++, and N++ 2 with N2, H2, D2, CH4, C2H2, C2H4, C2H6, C3H8 and the deuterated hydrocarbon analogs, as well as the recombination reactions of N+ 2, N+, N++ 2, and N++. Production processes, lifetimes, and quenching by collisions with N2 of all reactant species are reviewed. The N (4 S) state is reactive with radicals and its reactions with CH2, CH3, C2H3, and C2H5 are reviewed. Metastable states N2(A3Σ+u), N (2 D), and N (2 P) are either reactive or quenched by collisions with the target molecules reviewed. The reactions of N+ (1 D) have similar rate constants as N+ (3 P), but the product branching ratios differ significantly. Temperature effects and the role of the kinetic energy content of reactants are investigated. In all cases, experimental uncertainties of laboratory data are reported or estimated. Recommended values with uncertainties, or estimated values when no data are available, are given for rate constants and product branching ratios at 300 K and at the atmospheric temperature range of Titan (150-200 K for neutral reactions and 150 K for ion reactions).

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CRITICAL REVIEW OF N, N+, N+ 2, N++, And N++ 2 MAIN PRODUCTION PROCESSES AND REACTIONS OF RELEVANCE TO TITAN'S ATMOSPHERE

The binary-encounter collision theory has been applied to the calculation of the G-values for the ionization and excitation of noble gases irradiated by 100 keV electrons. The G-values obtained were as follows in the order of He, Ne, Ar, Kr, and Xe: 2.27, 2.19, 2.81, 3.20, 3.45 for G(electrons), 0.85, 1.55, 1.92, 1.64, 1.51 for G(singlet states), and 0.17, 0.07, 0.13, 0.23, 0.39 for G(triplet states). The method of the calculation and the significance of the results were discussed.

The Estimation of the G-Values for the Ionization and Excitation of Noble Gases Irradiated by 100 keV Electrons

The binary-encounter collision theory is applied to calculate the G-values for the ionization and excitation of methane, ammonia, and water irradiated by 100 keV electrons. Double collision of the incident electron in a molecule is also taken into account. On the assumption of the occurrence of certain reactions in the systems, the G-values for electrons, various radicals, and several final products were estimated. Some of the results are as follows: the G-values for electrons were 3.60 for methane, 3.56 for ammonia, and 3.00 for water. These values are in fair agreement with the experimental values: 3.6 for methane, 3.8 for ammonia, and 3.3 for water. The calculated G-value for hot hydrogen atoms was about 1.0 for all three compounds. The ratios of the G-value for excitation to that for electrons are 1.1 for methane, 1.5 for ammonia, and 1.7 for water. An estimation was also made of the G-value for the emission of highly-excited hydrogen atoms using reported cross sections. The G-values are 0.1 for metha...

The Estimation of the G-Values for Ionization and Excitation of Ten-Electron Molecules: Methane, Ammonia, and Water Irradiated by 100 keV Electrons

Kinetic isotope effects in the reaction H + C2H4 → C2H5

Reactions of NH with C2H6 and C3H8 in the liquid phase

The yields for the ionization and excitation from each molecular orbital of a water molecule irradiated by 10 keV electrons were calculated using the classical binary-encounter approximation. On further assuming fragmentation processes of the excited or ionized states consistent with the photochemical and mass spectrometrical results in the literature, we obtained, as the radiolysis yields of water vapor: G(electron)=2.96; G(OH−)=0.04; G(H3O+)=3.00; G(H)=4.83–5.21, including G(‘hot’ H-atoms)≤0.87; G(H2)=0.28–1.15; G(O)=0.83–1.21; G(OH)=6.70–7.08, and G(–H2O)=G(ionized water)+G(excited water)=2.91+4.96=7.87.

Shin Sato

Papers

The Estimation of the G-Values for the Ionization and Excitation of Noble Gases Irradiated by 100 keV Electrons

The Estimation of the G-Values for Ionization and Excitation of Ten-Electron Molecules: Methane, Ammonia, and Water Irradiated by 100 keV Electrons

Kinetic isotope effects in the reaction H + C2H4 → C2H5

Reactions of NH with C2H6 and C3H8 in the liquid phase

The Calculation of the Primary Radiolysis Yield of Water Vapor Irradiated by 10-keV Electrons