Rev. Sci. Instrum. 50, 1002 (1979] were used with either Re or spring-steel gaskets to compress the samples, which consisted of cryogenically loaded Xe along with Fe powder (<20 |xm grain size) and less than 10 volume % fine-grained ruby (<5 |xm grain size); the latter is used for pressure calibration [H. K. Mao, P. M. Bell, J. W. Shaner, J. Steinberg, J. Appl. Phys. 49, 3276 (1978)]. Samples were heated inside the diamond cell by means of a Quantronix 117 continuous-wave Nd:YAG laser operated in the TEM00 mode, with average temperatures ranging from 1860 (±180) to 3080 (±300) K being documented by imaging spectroradiometry [R. Jeanloz and A. Kavner, Philos. Trans. R. Soc. London Ser. A 354, 1279(1996]. 20. Diffraction patterns were obtained at high pressures and room temperature (before and after laser heating) using a Rigaku 12 kW/mm 2 rotating anode source of monochromatized Mo Ka x-rays. The diffraction patterns were collected in angular-dispersive mode with film and analyzed by methods described elsewhere [J. H. Nguyen and R. Jeanloz, Rev. Sci. Instrum. 64, 3456 (1993)].Epoxides are versatile building blocks for organic synthesis. However, terminal epoxides are arguably the most important subclass of these compounds, and no general and practical method exists for their production in enantiomerically pure form. Terminal epoxides are available very inexpensively as racemic mixtures, and kinetic resolution is an attractive strategy forthe production of optically active epoxides, given an economical and operationally simple method. Readily accessible synthetic catalysts (chiral cobaltbased salen complexes) have been used for the efficient asymmetric hydrolysis of terminal epoxides. This process uses water as the only reagent, no added'solvent, and low loadings of a recyclable catalyst (<0.5 mole percent), and it affords highly valuable terminal epoxides and 1,2-diols in high yield with high enantiomeric enrichment.Asymmetric catalysis provides access t o addition to carbonyl compounds (2). Both optically active epoxides either by oxygen-strategies have been developed t o varying atom transfer to alkenes ( J ) or by carbene degrees, but significant gaps still exist in the scope of these methodologies. For example,

We report the near-surface doping of a ZnO single crystal by ion implantation with nitrogen and titanium. Secondary-ion-mass spectroscopy shows that the doping depth is approximately 80 nm ͑N͒ and 50 nm ͑Ti͒. The DAP photoluminescence centered at 3.232 eV is observed from both the undoped and doped ZnO single-crystal samples. The luminescence spectrum of the nitrogen-doped sample shows enhancement of the DAP transition compared to the "pure" ZnO sample. The acceptor energy is calculated to be 177 meV, consistent with nitrogen as the acceptor in DAP luminescence. The DAP recombination lifetime is found to be ϳ5.5 ns. The temperature evolution of spectra shows the gradual transition from DAP luminescence to electron+ acceptor recombination luminescence at temperatures above 37 K. Our experimental results suggest that ion implantation is an effective way of doping nitrogen into ZnO.

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Optical properties of metal ͑Al, Ag, Sb, and Sn͒-ion-implanted ZnO films have been studied by ultraviolet-visible spectroscopy and spectroscopic ellipsometric techniques. The effects of metal-ion doping on the optical band gap ͑E g ͒, refractive index ͑n͒, and extinction coefficient ͑k͒ of nanocrystalline ZnO films have been studied for the similar implantation dose of all the metal ions. The ellipsometric spectra of the ion-implanted samples could be well described by considering an air/roughness/ZnO-M ͑layer 1͒/ZnO ͑layer 2͒/glass model. The band gap of ZnO films increases with Al ion doping and decreases with doping of Ag, Sb, and Sn ions. The refractive index of ZnO films in the visible spectral region increases substantially on Sb and Sn ion doping, while it decreases to some extent with Al ion doping.

This investigation presents a detailed examination of the relative reliability of the comparative and absolute rate methods as they are applied to kinetic studies in the single-pulse shock tube. For this purpose two previously studied reactions, the thermal elimination of HCI from ethyl chloride and n-propyl chloride, were selected and mixtures of these compounds were shock heated to temperatures in the range of 960"-1100"K. The experimental results were analyzed by both methods and the rate constants obtained from these analyses are compared with those of previous studies. The advantages and shortcomings of both methods are noted and it is concluded that reliable kinetic data can be obtained by the absolute rate (isolation technique) method with careful examination of the gas-dynamic flow conditions and taking cognizance of the incident shock deceleration. The limitations of the comparative rate technique encountered in the present study were similar to those detailed in previous investigations.