Localized vibrational modes of interstitial oxygen and oxygen complexes in GaP

The i.r. absorption spectrum of GaP in the range 500–1500 cm^?1 is found to contain several sharp impurity modes. Doping and annealing experiments show some of these modes to be connected with the presence of oxygen. Such modes are found to be present in all samples of nominally undoped LEC grown GaP. From the unusually high frequency of the modes and correlations with other semiconductors it is concluded that the oxygen is situated in interstitual sites. A linear chain model is developed to explain the frequency of the mode using force constants similar to those in oxygen doped silicon. The model is then used to predict the vibrational frequencies and the absorption strengths of several types of complex involving the oxygen interstitial. These calculations together with the absorption spectra suggest that oxygen-carbon and oxygen-boron complexes are also present in LEC grown GaP.     

Heavy-ion one-neutron transfer reactions involving 13C: (I). Spectroscopic factor products

The total cross sections of some heavy-ion one-neutron transfer reactions involving ¹³C, which lead to excited states of one of the final nuclei, have been measured at energies below the Coulomb barrier. Products of the neutron spectroscopic factors in the initial and final states have been extracted using a Coulomb wave Born approximation, and have been compared with theory.     

Heterocycles from ketenimines XI. Oxindoles

The reaction of ketenimines with heterocyclic N-oxides yields N-substituted oxindoles. Hydrolysis of these adducts or acid work-up of the original reaction mixtures leads directly to oxindoles in which the nitrogen atom is unsubstituted.     

Stimulated Raman emission at 9.2 μm from hydrogen gas

Light at 1.06 μm from a mode-locked Nd:YAG laser has been successfully down-converted by two vibrational stimulated Raman shifts in H₂ gas. Approximately 1 MW of power was produced at second-Stokes wavelength, 9.20 μm. Many other rational and vibrational shifts were observed, up to the seventh anti-Stokes at 260 nm.     

VLPP unimolecular rate theory

The exact theory is derived for the thermal unimolecular decomposition of gas-phase molecules activated and deactivated exclusively through heterogeneous collisions with the walls of a spherical vessel. This theory is appropriate for the treatment of very-low-pressure pyrolysis (VLPP) experiments and other experiments carried out at very low pressures. It is shown, however, that the exact theory is closely approximated by ordinary gas-phase unimolecular rate theory and that for practical application to experiments the results of both theories are indistinguishable.     

An ordered array of cadmium clusters assembled in zeolite A

We report the assembly of a cubic array of cationic cadmium clusters encapsulated in zeolite A, and its characterization through Rietveld analysis of powder synchrotron X-ray diffraction data and high resolution transmission electron microscopy.     

Precise estimate of fundamental in-vivo MT parameters in human brain in clinically feasible times

A methodology is presented for extracting precise quantitative MT parameters using a magnetisation-prepared spoiled gradient echo sequence. This method, based on a new mathematical model, provides relaxation parameters for human brain in-vitro and in-vivo. The in-vivo parameters have been obtained from three different regions of normal white matter: occipital white matter, frontal white matter and centrum semiovale; two regions of normal grey matter: cerebral cortex and cerebellum, and from five regions with MS lesions. All this has been achieved using MT images collected within a timeframe that is clinically feasible. We hope that this new technique will shed light on the properties and dynamics of water compartments within the brain.