Kinetics of the reaction F + 1,2-dibromo-1,1,2-trifluoroethane

The title reaction was studied in a standard flow system with F atoms produced by RF discharge in F₂-He mixture. Analysis was by gas chromatography using electron capture detection. There were two major products, identified as CF₂BrCF₂H and CF₂BrCF₂Br, plus presumably HF which was not detectable. The overall rate of disappearance of reactant was found to be of mixed one and one-half order, indicating a complex reaction. A mechanism is proposed comprising six steps and involving two radical species CF₂Br?FBr (R₁) and CF₂Br?F₂. The 300 K rate constant for the initial step F + reactant → HF + R₁ is evaluated to be 2.2 × 10^?13 cm³/molec·s, which fits in with rates of other saturated hydrocarbon reactants containing one hydrogen atom, thus supporting the view that in this class of reactants the rates of reactions of the type F + saturated hydrocarbon depend mainly on the number of hydrogen atoms in the reactant.     

The Tolerance Approach to Sensitivity Analysis of Matrix Coefficients in Linear Programming: General Perturbations

In the tolerance approach to sensitivity analysis of matrix coefficients in a linear programme, the maximum tolerance percentage characterizes the largest percentage within which selected matrix coefficients may vary simultaneously and independently while retaining the same set of optimal basic variables. While it is difficult to calculate exactly the maximum tolerance percentage under perturbations in multiple rows or columns, we show herein how it can be approximated.     

Directed desorption as a probe of the structure of the desorption site

This paper attempts to assess the effects of surface structure on the angular variation of the desorption flux. Quantum calculations are done which show that if the gas-surface interaction potential is sufficiently corrugated in the neighborhood of the desorption site, and the adsorbate molecules desorb without going through a mobile precursor state, then they desorb preferentially in the direction of the surface normal. An activation barrier for adsorption need not be invoked. The predictions of the model agree with recent experiments. More theoretical and experimental verification of the model is needed, but it appears that it should be possible to use a directed desorption experiment to probe the forces on a molecule when it is about to desorb from a surface.     

A nonlinear model for toroidal drift modes driven by ion pressure gradients

A model for the nonlinear toroidal drift modes is shwon to have an asymptotically stable solution consistent with previous saturation estimates.     

Fe2(co)g in tetrahydrofuran or under sonochemical conditions as convenient practical routes to π-allyltricarbonyliron lactone complexes

A series of alkenyl epoxides were converted into their corresponding π-allyltricarbonyliron lactone complexes by either treatment with tetrahydrofuran solutions of Fe₂(CO)₉ at room temperature, or in hydrocarbon solvents with Fe₂(CO)₉ under ultrasonification conditions. The new routes constitute convenient practical alternatives to presently existing methodology.     

Electrokinetic control of fluid in plastified laser-printed poly(ethylene terephthalate)-toner microchips

The application of plastified laser-printed poly(ethylene terephthalate)(PET)-toner microchips to capillary electrophoresis was investigated. Electroosmotic flow was observed in the direction of the cathode for the buffer system studied (phosphate, pH 3–10). Average electroosmotic mobilities of 1.71×10^–4 to 4.35×10^–4 cm² V^–1 s^–1 were observed from pH 3 to 10. This variation suggests that silica fillers in the toner and on the surface of the polymer dominate the zeta potential of the material, which is also confirmed by XPS measurements. Dopamine and catechol were used as model analytes for microchip electrophoresis in combination with electrochemical detection. Results show that these two analytes can be efficiently separated and detected electrochemically with the plastified laser-printed PET-toner microchips.     

Zur Temperaturabhängigkeit der elastischen Konstanten kubischer Gitter

An equation involving the temperature variations of the elastic constants of cubic metals is implicitly contained in the Bhatia model for cubic metals. This result is of interest because it is closely connected with the question of the equilibrium condition in lattice dynamics. Recent experimental results on the elastic constants and thermal expansion coefficients of copper and aluminum are compared with a formula derived from the Bhatia theory. The experimental results are not yet sufficiently accurate to permit a detailed comparison with the theory though rough agreement is found.     

Analytical solution of vibrational–rotational energy transfer in the dissociation and relaxation of N2, Br2, and CO at high temperature

An approximate analytical solution of relaxation in a low-pressure system with exponential transition probabilities is given for vibrational–rotational energy transfer in the dissociation of diatomics. The main assumption is that the rotational degrees of freedom are in thermal equilibrium at all times, and that the barrier to dissociation in the vibrational–rotational plane is linear and asymmetric. The theory is applied to high-temperature dissociations of N₂, Br₂, and CO in excess argon, with satisfactory agreement with available experimental data.