No abstract available

[en] The intermolecular kinetic isotope effect for the title reaction has been investigated using a moderated nuclear recoil technique. The following Arrhenius temperature dependence was obtained: k)2/k)2 = (1.04plus-or-minus0.06)exp(382plus-or-minus35)/RT. This result is in quantitative agreement with an independent study based upon a discharge flow reactor method. The advantages and limitations of the nuclear recoil procedure are considered, and relevant literature results are critically reviewed

[en] Isotope effects were investigated at the surface of aqueous lithium and calcium salt solutions. The dependence on the temperature in the gas phase was determined. The surfaces of the solutions were isolated by spray experiments. In the case of calcium salt solutions an enrichment of the lighter isotope ⁴⁰Ca in relation to the heavier isotopes ⁴⁴Ca and ⁴⁸Ca was found at the solution surface. The experiments with lithium fluoride and lithium iodide gave inverse isotope effects. The calcium isotope effect could be qualitatively explained by the Gibbs theorem. The isotope separation of lithium possibly can be referred to the more covalent than ionic bonding character of lithium compounds at the solution surface. (orig.)

[en] When boron nitride is phosphidized over the temperature range 800-900⁰C, with holding for 1 to 4 hours, the material obtained is a multiphase system, the chief component of which is BN. P₂O₅, BP, and PON were detected radiographically, and the type of photoluminescent spectrum exhibited by this material was found to depend on its phase composition. (author)

[en] A medium-pressure (1 Torr), large-diameter (10 cm) flow tube has been used to measure rate coefficients at 298 degreeK for (a) total relaxation (sum of vibrational--vibrational and vibrational--rotational, translational processes) of HF(v=1, 2, 3, 4, and 5) by HF, (b) relaxation of DF(1, 2, 3, and 4) by HF, and (c) over-all relaxation of DF(v=1, 2, 3, and 4) by D₂. The chemically produced vibrationally excited HF or DF species have been studied by monitoring their vibrational--rotational emission in a fast-flow system. The rate coefficient for the relaxation of HF(1) by HF is 5.3times10⁴ sec^-1center-dotTorr^-1. The measured rate coefficients for the deexcitation of HF(v=2, 3, 4, and 5) by HF are 5.3times10⁵, 8.5times10⁵, 8.8times10⁵, and 2.8times10⁵ sec^-1center-dotTorr^-1, respectively. The rate coefficients for the vibrational--rotational, translational deexcitation from the upper vibrational levels of DF(v) by HF are found to have a nonlinear vibrational dependence. The rate coefficient for the relaxation of DF(v=1) by D₂ is 1.35times10⁴ sec^-1center-dotTorr^-1

No abstract available

[en] The intermolecular deuterium isotope effect for the photoinitiated bromination of cyclohexane and perdeuteriocyclohexane was determined in the vapor phase and in solution. Under conditions where the radicals formed do not transfer with hydrogen or deuterium bromide, a value for the vapor phase reaction of k/sub RH/k/k/sub RD/ = 5.4 +- 0.2 (20.8⁰) was found. In solution at concentrations of bromine (0.07-3.6 M) which are high enough to stop the transfer of the radicals that are free of the solvent cage, with the low concentrations of hydrogen or deuterium bromide formed at low conversion, the value obtained for k/sub RH//k/sub RD/ = 4.3 +- 0.2. The difference between the vapor phase and solution results is attributed to a cage reversal reaction, between the radical hydrogen bromide pair, that is competitive with diffusion. At concentrations of molecular bromine (10-18 M) that are high enough to scavenge radicals from the solvent cage, the value obtained for k/sub RH//k/sub RD/ is the same as that found in the vapor phase. Under conditions where mixtures of the reactants (C₆D₁₂:C₆H₁₂:Br₂, 1:1:1) were allowed to completely react the value determined for k/sub RH//k/sub RD/ = 3.1 +- 0.01 can be attributed to both internal and external reversal reactions. (auth)

[en] Sections for the system Eu₂O₃-Gd₂O₃-Ta₂O₅ containing 25, 50 and 75 mol.%. Ta₂O₅ at 1250⁰C were studied by the X-ray, electron-microscope and luminescent techniques. It was established that there exist solid solutions with a cubic, monoclinic and rhombic type base, respectively, throughout the X value interval for (Eusub(x)Gdsub(1-x)₃ TaO₇, Eusub(x)Gdsub(1-x) Ta₃O₉, and Eusub(x)Gdsub(1-x) TaO₄. The variation in elementary cell parameters does not obey Vegard's law. The anomalies in variation as x increases are observed close to X=0.15 and 0.35. (author)

No abstract available

[en] The design, fabrication, and operation of a special plant growth chamber system utilized in the biosynthesis production of ¹⁴C labeled tobacco plant material are described. The controlled environmental factors of the system were relative humidity, temperature, carbon dioxide, nutrients and auxiliary lighting. Four plants of Nicotiana tabacum L. cv. Coker 254 were grown for five weeks in the ¹⁴CO₂ atmosphere of the growth chamber. The four-plant harvest produced a total dry weight yield of 420 g of uniformly labeled ¹⁴C-tobacco plant material with an average specific activity of 614 nCi/mg of carbon. (author)