On a domination property for vector maximization with respect to cones

We give a corrected version of Theorem 2.1 of Ref. 1.The author is indebted to D. T. Luc, Hungarian Academy of Sciences, Budapest, Hungary, for pointing out his error in the proof of the original version of Theorem 2.1 in Ref. 1.     

The kinetics and thermochemistry of S2F10 pyrolysis

Data on the kinetics of S₂F₁₀ pyrolysis, which gives SF₄ + SF₆, have been reinterpreted to give a value for the equilibrium constant of S₂F₁₀ ? SF₄ + SF₆. This, together with statistical estimates of the entropy and heat capacity of S₂F₁₀, can be used to give for this reaction values of ΔH = 19.7 ± 1.0 kcal/mole and ΔS = 47.6 ± 2 gibbs/mole. ΔH(S₂F₁₀) = –494 kcal/mole. A compatible mechanism is shown to be S₂F₁₀ ? 2SF₅ (fast); 2SF₅ ? SF₆ + SF₄ (slow) with step 2 rate-determining. The overall, best first order rate constant is proposed as k_meas = 10^{17.42–43.0/θ} sec^?1 = K₁k₂, where θ = 2.303RT in kcal/mole. Independent measurements of δH and S° for the SF₅ radical, permits the evaluation of the equilibrium constant K₁ = 10^{8.92–(27.1 ± 6)/θ} l./mole-sec and yields k₂ = 10^{8.50–15.9/θ} l./mole-sec. The observed homogeneous catalysis by NO and CHCl ? CHCl can be explained in terms of a direct abstraction of F from S₂F₁₀ : C + S₂F₁₀ → CF + S₂F₉, followed by S₂F₉ → SF₅ + SF₄ and SF₅ + CF ? SF₆ + C (C ? NO or C₂H₂Cl₂).     

Very low-pressure pyrolysis: VI. The decomposition of ethyl acetate

The pyrolysis of ethyl acetate has been studied by the very low-pressure pyrolysis (VLPP) technique. The results obtained agree well with the previously determined high-pressure Arrhenius parameters where log k_∞ = 12.6 ? 48.0/θ. The rate constants given by these parameters have also been shown to be consistent with the predictions of the RRK and RRKM theories and demonstrate the applicability of the technique to the study of thermal decompositions.     

Self-Reaction of HO2 and DO2: Negative temperature dependence and pressure effects

The negative temperature dependence, pressure dependence, and isotope effects of the self-reaction of HO₂ are modeled, using RRKM theory, by assuming that the reaction proceeds via a cyclic, hydrogen-bonded intermediate. The negative temperature dependence is due to a tight transition state, with a negative threshold energy relative to reactants, for decomposition of the intermediate to products. A symmetric structure for this transition state reproduces the observed isotope effect. The weak pressure dependence for DO₂ self-reaction is due to the approach to the high-pressure limit. Addition of a polar collision partner, such as ammonia or water vapor, enhances the rate by forming an adduct that reacts to produce deexcited intermediate. A detailed model is presented to fit the data for these effects. Large ammonia concentrations should make it possible to reach the high-pressure limit of the self-reaction of HO₂.     

Rate constants for alkyl radical recombination. II. The isopropyl radical

Products of radical combination from the free-radical buffer system \documentclass{article}\usepackage{amssymb}\pagestyle{empty}\begin{document}$${{\rm R}^{\rm .} + {\rm R}^{\rm '} {\rm I}\mathop {\leftrightharpoons}\limits^{{\rm K}_{{\rm RR}}}{\rm RI} + {\rm R}^{'}}$$\end{document}. have been analyzed for the two cases, R = Me, R′ = iPr and R = Et, R′ = iPr. Results are consistent with the previously examined system where R = Me, R′ = Et, and give a value of k_P for iPr· combination of 10^8.6±1.1 M^?1 sec^?1.     

Search for γ-rays emitted in the formation of a fission isomer

A search for γ-rays preceding isomeric fission in the reaction²³⁸U(α, 2n)^240mPu yielded negative results. Upper limits are given for the number of unconverted photons per isomer formed.     

Mechanism of the pyrolysis of C2HCl5, molecular and radical steps

An analysis of the thermochemistry of the kinetic parameters of the elementary reactions involved in the pyrolysis of pentachloroethane has resolved several disputed, unclarified, or inconsistent aspects of the reaction mechanism. The resulting mechanisms for the inhibited and uninhibited pyrolysis account for all reported experimental findings. On the basis of this interpretation, first experimentally based values have been derived for the following: DH⁰(CCl₃–CHCl₂) = 79.0 ± 1.0 kcal/mol, ΔH${}_{\text{f}}^{\text{0}}$(CHCl₂) = 25.7 ± 1.0 kcal/mol, and E₁ = 59.7 ± 1.0 kcal/mol C₂HCl₅ .     

Kinetics and thermochemistry of the gas phase reaction of methyl ethyl ketone with iodine. II. The heat of formation and unimolecular decomposition of 2-iodo-3-butanone

Equilibrium constants for the reaction CH₃COCH₂CH₃ + I₂ ? CH₃COCHICH₃ + HI have been computed to fit the kinetics of the reaction of iodine atoms with methyl ethyl ketone. From a calculated value of S(CH₃COCHICH₃) = 93.9 ± 1.0 gibbs/mole and the experimental equilibrium constants, ΔH(CH₃COCHICH₃) is found to be ?38.2 ± 0.6 kcal/mole. The Δ(ΔH) value on substitution of a hydrogen atom by an iodine atom in the title compound is compared with that for isopropyl iodide. The relative instability of 2-iodo-3-butanone (3.4 kcal/mole) is presented as further evidence for intramolecular coulombic interaction between partial charges in polar molecules. The unimolecular decomposition of 2-iodo-3-butanone to methyl vinyl ketone and hydrogen iodide was also measured in the same system. This reaction is relatively slow compared to the formation of the above equilibrium. Rate constants for the reaction over the temperature range 281°–355°C fit the Arrhenius equation: where θ = 2.303RT kcal/mole. The stability of both the ground and transition states is discussed in comparing this activation energy with that reported for the unimolecular elimination of hydrogen iodide from other secondary iodides. The kinetics of the reaction of hydrogen iodide with methyl vinyl ketone were also measured. The addition of HI to the double bond is not rate controlling, but it may be shown that the rate of formation of 1-iodo-3-butanone is more rapid than that for 2-iodo-3-butanone. Both four- and six-center transition complexes and iodine atom-catalyzed addition are discussed in analyzing the relative rates.