Steric effects on reaction rates II: Rate and equilibrium constants for oxidation of bicyclic alcohols

Equilibrium constants for oxidation of a series of bicyclic alcohols with cyclohexanone have been determined under Meerwein-Ponndorf conditions. The data provide the thermodynamic background for interpretation of the mechanism of alcohol oxidation and ketone reductions. Free energies of the equilibrium (ΔG_ox) are compared with values calculated by molecular mechanics.     

Evidence for strongly temperature-dependent A factors in alkane decomposition and high heats of formation for alkyl radicals

The experimental data on alkane decomposition from shock-tube and radical buffer studies and radical combination from very-low-pressure pyrolysis and modulation spectroscopy are shown to be consistent. They lead to experimental A factors which decrease by factors of 10–2000 from 300° to 1100°K. Heats of formation for ethyl, isopropyl, and t-butyl radicals have been found to be 10, 10 and 20 kJ higher than currently accepted numbers from metathesis reactions.     

Comparative study of guest charge-charge interactions within silica sol-gel

We investigated the effect of charge-charge interactions on the mobilities of rhodamine 6G (R6G), Nile Red, sulforhodamine B, and Oregon Green 514 (ORG) guest molecules within a silica sol-gel host as the guest charge progressed from positive to neutral to negative. Through classification of the mobility as fixed, tumbling, or intermediate behavior, we were able to distinguish differences in surface attraction as the guest charge was varied. On the basis of our results, an attractive charge (as tested by cationic R6G) does not contribute significantly to mobility within dry films. However, an increase in the cationic influence is observed in water-equilibrated environments. A comparison of ORG in dry and water- and phosphate-buffer-equilibrated films indicates that charge repulsion does significantly increase dye rotational mobility (to a maximum of 24 +/- 3% tumbling molecules). However, in view of the percentage of tumbling molecules found, charge-charge interactions do not appear to be the dominant force controlling guest mobility.     

Atomistic configurations and energetics of crack extension in silicon

We report the first atomistic determination of the minimum energy path for a series of bond ruptures to advance a crack front. Saddle-point configurations on (111) cleavage planes in Si reveal a steplike distribution of atomic displacements, implying a kink mechanism which is known to control dislocation mobility. Manifestations of lattice trapping and directional cleavage anisotropy are further elucidated.     

A convenient,one-step synthesis of optically active tertiary aminonaphthol and its applications in the highly enantioselective alkenylations of aldehydes

Optically active tertiary aminonaphthol 1 was obtained by a new, convenient procedure and was found to catalyze the enantioselective alkenylation of various aldehydes with high ee values, which provides a practical method for the synthesis of chiral (E)- allyl alcohols.     

Intrinsic mobility of a dissociated dislocation in silicon

Dislocation velocities in silicon in the experimental range of temperature and stress are studied a priori by combining a mechanistic treatment of elementary kink processes with activation energies obtained by atomistic calculations. Pronounced effects of intrinsic coupling of the dissociated partial dislocations are captured in kinetic Monte Carlo simulations, which are consistent with observed velocity variations with applied stress. As a result, the nature of "weak obstacles" to kink propagation, a long-standing postulate in previous data interpretation, is clarified. A striking new effect is predicted and offered for experimental verification when dislocation velocity shows nonmonotonic oscillatory behavior with increasing stress.     

Data acquisition in the EUDET project

The goal of the EUDET project is the development and construction of infrastructure to permit detector R&D for the international linear collider (ILC) with larger scale prototypes. It encompasses major detector components: the vertex detector, the tracker and the calorimeters. We describe here the status and plans of the project with emphasis on issues related to data acquisition for future test beam experiments.