Very-low-pressure pyrolysis of nitroso- and pentafluoronitrosobenzene C?NO bond dissociation energies

The high-pressure absolute rate constants for the decomposition of nitrosobenzene and pentafluoronitrosobenzene were determined using the very-low-pressure pyrolysis (VLPP) technique. Bond dissociation energies of DH⁰(C₆H₅? NO) = 51.5 ± 1 kcal/mole and DH⁰ (C₆F₅? NO) = 50.5 ± 1 kcal/mole could be deduced if the radical combination rate constant is set at log k_r(M^?1·sec^?1) = 10.0 ± 0.5 for both systems and the activation energy for combination is taken as 0 kcal/mole at 298°K. δH_f⁰(C₆H₅NO), δH_f⁰(C₆F₅NO), and δH_f⁰(C₆F₅) could be estimated from our kinetic data and group additivity. The values are 48.1 ± 1, –160 ± 2, and – 130.9 ± 2 kcal/mole, respectively. C–X bond dissociation energies of several perfluorinated phenyl compounds, DH⁰(C₆F₅–X), were obtained from the reported values of δH_f⁰(C₆F₅X) and our estimated δH_f⁰(C₆F₅) [X = H, CH₃, NO, Cl, F, CF₃, I, and OH].     

Curvature-dependent surface tension of a growing droplet

A ghost interface simulation technique is developed and applied to supersaturated Lennard-Jones liquid-vapor interfaces. It is shown that the surface tension decreases approximately linearly with the supersaturation ratio and that it vanishes at the spinodal. The effect leads to a curvature-dependent surface tension since, it is argued, the local supersaturation of the vapor above a droplet is greater than in the bulk due to slow diffusion in the vapor phase. An analytic approximation is given for the local supersaturation ratio, and an analytic expression for this contribution to Tolman's length is derived. The theory gives a smaller critical radius and reduces the free energy barrier to nucleation compared to classical homogeneous nucleation theory, which have important implications for the kinetics of droplet and bubble formation.     

Practical synthesis and elaboration of methyl 7-chloroindole-4-carboxylate

A synthesis of a previously unknown indole derivative is presented. The route reported herein allows for the preparation of multihundred gram quantities of material without any chromatographic purification. Conditions are presented for the Pd-catalyzed elaboration of one of the "diversity generating elements" of this important pharmacophore.     

Stereoselective synthesis of beta-(chloro)vinylsilanes using a regio- and (E)-stereoselective bis-stannylation of unsymmetrically substituted butadiynes: application to the synthesis of a masked triyne

[reaction: see text] A highly regio- and stereoselective bis-stannylation of unsymmetrically substituted butadiyne 3 provides bis-stannane 4. Selective lithiation of the internal tin residue effects a 1,4-retro-Brook rearrangement to afford vinylsilane 5. This was elaborated into the novel diethynylethene 1, which also functions as a masked triyne.     

Regulated and entangled photons from a single quantum Dot

We propose a new method of generating nonclassical optical field states. The method uses a semiconductor device, which consists of a single quantum dot as active medium embedded in a p- i- n junction and surrounded by a microcavity. Resonant tunneling of electrons and holes into the quantum dot ground states, together with the Pauli exclusion principle, produce regulated single photons or regulated pairs of photons. We propose that this device also has the unique potential to generate pairs of entangled photons at a well-defined repetition rate.     

Parity violation in elastic electron-proton scattering and the Proton's strange magnetic form factor

We report a new measurement of the parity-violating asymmetry in elastic electron scattering from the proton at backward scattering angles. This asymmetry is sensitive to the strange magnetic form factor of the proton as well as electroweak axial radiative corrections. The new measurement of A = -4.92+/-0.61+/-0.73 ppm provides a significant constraint on these quantities. The implications for the strange magnetic form factor are discussed in the context of theoretical estimates for the axial corrections.     

Trends in microdisk laser research and linear optical modelling

Research into microdisk lasers demonstrates new achievements both in the technology and in the associated physical effects and applications. Melting and rounding of the disk edge boosts the Q-factors due to improved surface smoothness. In-plane cavity shape is widely used as a design instrument. Optimal shaping of pumped area lowers the threshold power. Photonic molecules made of several microdisks as “photonic atoms” show lasing at several closely spaced frequencies. A microdisk with a single quantum dot as an active region is considered as the most promising system for realisation of a single photon emitter necessary for quantum computing. These new effects and devices can be simulated with accurate numerical techniques, developed recently for “warm-cavity” linear modelling, that are able to bring a new vision of the physics of lasing.     

Facet reflectivity in the presence of a diffracting corner

Results and new theory are presented for the uncoated and coated facet reflectivity of a shallowly buried waveguide, taking account of the diffracting corner present at the air–semiconductor interface. The corner effects are shown to be most significant in the case of coated facets. The analysis also predicts the asymmetry introduced into the radiation pattern.