Kinetics of hydrogen oxidation near the lower explosion limit in the kinetic region of chain termination has been studied. Major effects, causing deviations of the reaction kinetics from calculations by the linear theory of branched chain processes, are shown to be (1) the inhibition of the reacting mixture by the products of interaction of active centers with vacuum grease or with impurities contained in it and (2) the heterogeneous negative interaction of reaction active centers. The kinetics of hydrogen oxidation in this region has been calculated with consideration of the heterogeneous negative chain interaction. A set of parameters has been obtained that make it possible to determine by the shape of the kinetic curves the sign and the value of nonlinear interaction of chains near the lower explosion limit. It has been shown that the experimental data are in good agreement with the calculations, provided the heterogeneous negative chain interaction is taken into consideration and the inhibiting effect of impurities is eliminated:The rate of heterogeneous generation of chains on a quartz surface treated with hydrofluoric or boric acid has been determined.
The rate constants for the reactions of OH radicals with the 1-bromopropane, 2-bromopropane, and propane were measured using the flash photolysis resonance fluorescence technique over the temperature range between 210 and 480 K. Arrhenius plots exhibit a noticeable curvature, and the rate constants can be represented using a three-parameter modified Arrhenius expression over the temperature range of the experiments with ca. 2% precision. Such a fit also describes the available high-temperature data for propane quite well. The best three-parameter fits to the data are: k C 3 H 8 (T) ) 1.96 × 10 -12 × (T/298) 1.83 × exp{-167/T} cm 3 molecule -1 s -1 ; k nPB (T) ) 2.99 × 10 -13 × (T/298) 2.79 × exp{+369/T} cm 3 molecule -1 s -1 ; and k iPB (T) ) 1.66 × 10 -13 × (T/298) 2.95 × exp{+461/T} cm 3 molecule -1 s -1 . For the low temperature range of atmospheric interest, the reaction rate constants can be accurately presented by standard Arrhenius expressions. Based on the available low-temperature data the following rate constants can be recommended for the purpose of atmospheric modeling: k C 3 H 8 (T < 300 K) ) 8.66 × 10 -12 × exp{-615/T} cm 3 molecule -1 s -1 ; k nPB (T < 300 K) ) 3.03 × 10 -12 × exp{-330/T} cm 3 molecule -1 s -1 ; k iPB (T < 300 K) ) 1.77 × 10 -12 × exp{-260/T} cm 3 molecule -1 s -1 . Atmospheric lifetimes were estimated to be ca. 14, 14, and 19 days for CH 3 CH 2 CH 3 , CH 2 BrCH 2 CH 3 , and CH 3 CHBrCH 3 , respectively. The ultraviolet absorption spectra of these bromopropanes were measured between 164 and 270 nm.
Superconducting proximity devices using low-dimensional semiconducting elements enable a ballistic regime in the proximity transport. The use of topological insulators in such devices is considered promising owing to the peculiar transport properties these materials offer, as well the hope of inducing topological superconductivity and Majorana phenomena via proximity effects. Here we demonstrate the fabrication and superconducting properties of proximity Josephson devices integrating nanocrystals single of Bi 2 Te 2.3 Se 0.7 with a thickness of a few unit cells. Single junctions display typical characteristics of planar Josephson devices; junctions integrating two nanocrystals behave as nanodimensional superconducting quantum interference devices. A peculiar temperature and magnetic field evolution of the Josephson current along with the observed excess current effect point towards the ballistic proximity regime of topological channels. This suggests the proposed devices are promising for testing topological superconducting phenomena in two-dimensions.
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