Six-dimensional quasiclassical and quantum dynamics of H2 dissociation on the c(2 × 2)-Ti/Al(100) surface

Based on a slab model of H(2) dissociation on a c(2 × 2) structure with Ti atoms in the first and third layers of Al(100), a six-dimensional (6D) potential energy surface (PES) has been built. In this PES, a molecular adsorption well with a depth of 0.45 eV is present in front of a barrier of height 0.13 eV. Using this PES, H(2) dissociation probabilities are calculated by the classical trajectory (CT), the quasiclassical trajectory (QCT), and the time-dependent wave-packet (TDWP) method. The QCT study shows that trajectories can be trapped by the molecular adsorption well. Higher incident energy can lead to direct H(2) dissociation. Vibrational pre-excitation is the most efficient way to promote direct dissociation without trapping. We find that both rotational and vibrational excitation have efficacies close to 1.0 in the entire range of incident energies investigated, which supports the randomization in the initial conditions making the reaction rate solely dependent on the total (internal and translational) energy. The H(2) dissociation probabilities from quantum dynamics are in reasonable agreement with the QCT results in the energy range 50-200 meV, except for some fluctuations. However, the TDWP results considerably exceed the QCT results in the energy range 200-850 meV. The CT reaction probabilities are too low compared with the quantum dynamical results.     

Measurements on arc discharges. In nitrogen at 1 atm and higher pressure

Summary After preliminary experiments in different gases the arc between carbon electrodes in nitrogen is investigated more closely. The axial electric field strength between homogeneous carbon electrodes (mainly at 3–6 A and 1–4 atm) and also in arcs with KCl in the anode (at 4 A and 1–5 atm) proves to be a linear function of the pressure. The field strength is higher than in air and is reduced by the KCl. The sum of cathode- and anode-fall is found to be independent of the pressure. The central temperature in the arc without KCl was hard to measure, because self-absorption influenced the intensity ratios of the molecular bands in the spectrum. With KCl this difficulty did not appear, and temperatures were measured of about 7000°K, slightly increasing with the nitrogen pressure. Because the carbon electrodes evaporate much more slowly than in air, the arc in nitrogen is less stationary than in air; this hindered the measurements.     

Structure elucidation and 1H/13C NMR spectral assignments of four trabectedin related compounds

This article presents the structure elucidation of four new compounds, formed during the hemisynthetic preparation of trabectedin, an anti-tumor natural product from Ecteinascidia turbinata. We report herein on the use of UV, MS and NMR spectroscopic data along with (1)H and (13)C spectral assignments obtained by means of 1D and 2D homo- and heteronuclear NMR techniques.     

α-Alkyl-α-aminosilanes: Synthesis via Alkylation and Hydrosilylation

The readily available aminomethylsilanes can be utilized to prepare the less available α-alkyl-α-aminosilanes. Versatile t-butoxy-carbonal (Boc) derivatives can be metalated between nitrogen and silicon, and then alkylated by an electrophile at this position. Two alternative procedures were also developed, including an aza-reverse-Brook rearrangement of metalated N-silylcarbamates and hydrosilylation of N-alkenylcarbamates. © 1997 by John Wiley & Sons, Ltd.     

Effect of Air-excess on Blends of RON70 Partially Premixed Combustion

Partially Premixed Combustion (PPC) is a combustion concept that aims to provide combustion with low smoke and NOx emissions and a high thermal efficiency. Extending the ignition delay to enhance premixing, avoiding spray-driven combustion, and controlling temperature at an optimum level through use of suitable dilution levels has been recognized as a key factor to achieve such a concept. Fuels with high auto-ignition resistance do extend ignition delay. In this work three ternary blends of an alcohol (ethanol or n-butanol), n-heptane and iso-octane with a target research octane number (RON) of 70 are studied. RON70 was earlier found to be close to optimal for PPC over a large load range. The objective of this research is to analyze the sensitivity of the combustion parameters to changes in air-excess ratio when using these three blends. The engine was operated at 1250 rpm and 1000 bar injection pressure with a single injection strategy. Results revealed that efficiency was increased from rich to lean combustion, and these three blends show distinct premixed combustion even in lean PPC operation. The premixed fraction of combustion however reduces with the increase of air-excess ratio, which is especially apparent for PRF70 which consists of n-heptane and iso-octane alone.     

Structural and optical analysis of size-controlled InAs quantum dashes

Self-organized InAs and InGaAs quantum dashes have been investigated by chemically sensitive scanning transmission electron microscopy and photoluminescence spectroscopy. The quantum dashes exhibit a triangular cross section. Using electron energy loss spectroscopy, we show that no intermixing between quantum dashes and embedding barrier occurs during growth. By adjusting the nominal thickness of the InAs layer, the emission wavelength of the InAs quantum dashes can be tuned between 1.37 and 1.9 μm in a straightforward way.     

A classical dynamics method for H2 diffraction from metal surfaces

We present a discretization method that allows one to interpret measurements on diffraction of diatomic molecules from solid surfaces using six-dimensional (6D) classical trajectory calculations. It has been applied to the D2NiAl(110) and H2Pd(111) systems (which are models for activated and nonactivated dissociative chemisorption, respectively) using realistic potential energy surfaces obtained from first principles. Comparisons with experimental results and 6D quantum dynamical calculations show that, in general, the method is able to predict the relative intensity of the most important diffraction peaks. We therefore conclude that classical mechanics can be an efficient guide for experimentalists in the search for the most significant diffraction channels.     

EFFECT OF THE PHYSICAL STATE OF PHOSPHOLIPID ON RHODOPSIN REGENERATION FROM RETINYLIDENE PHOSPHOLIPID

Abstract— Rhodopsin regeneration in rod membranes involves reactions of all -trans retinal (released from bleached pigment) with phosphatidylethanolamine, photic isomerization of retinal, and binding of 11-cis retinal to opsin. This investigation demonstrated that formation of retinylidene phospholipid and retinal binding to opsin were both affected by the physical state of phospholipid. A fluid membraneous environment provided by the acyl chains of phospholipid was essential for these reactions to proceed efficiently. The retinal moiety of retinylidene phospholipid appeared to be directly transferred to opsin by transimination.