Taking advantage of our knowledge of the capacity of DIBAL-H to de-O-alkylate, we propose an alternative mechanism for a spiroketal rearrangement described by E. Suàrez. We also show that this proposal can account for the formation of the secondary product, whose original structure we propose to correct. 相似文献
Buffer gas beam coolers may become excellent beam preparation devices for high-resolution mass separation. The small beam
emittance provided makes efficient isobar resolution a realistic goal. In order to fulfill the needs of future facilities
providing high-intensity beams of rare isotopes, it is desirable to increase the beam intensity limit of such devices from
typically several tens of nanoamperes to microamperes. This requires the usage of high-voltage radiofrequencies in a low-pressure
gas environment. A buffer gas beam cooler, dedicated to this purpose, is under development at the NSCL. The study of voltage
breakdowns under such conditions and the design of an electrode system minimizing them is mandatory.
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The magnetotransport in a nondegenerate quasi-one-dimensional (Q1D) electron system over superfluid helium has been investigated experimentally. The measurements are performed in the presence of a perpendicular magnetic field B up to 2.6 T in the temperature range T=0.48–2.05 K in the system of conducting channels of 100–400 nm width. It is shown that the value of longitudinal magnetoresistance ρxx increases with B. In the electron-gas scattering region (T>0.9 ), the behaviour of ρxx agrees with classical Drude law. In the quantum transport regime, the self-consistent Born approximation (SCBA) theory for a 2D electron system over liquid helium describes the experimental data qualitatively. The deviation due to the difference of the experimentally studied Q1D system of the electrons in a parabolic potential well differs from theoretically analysed one. The experimental data agree with the theoretical calculation for the Q1D electron system at the weak magnetic field and the low temperature.
The negative magnetoresistance of the conducting channels has been observed in both the gas- and the ripplon-scattering region. These effects have been explained by weak carrier localization on the gas atoms at high temperature and by display of the quantum magnetotransport features in a mesoscopic system at low temperature. 相似文献
Experimental and theoretical investigations of the spectroscopy of molecules in superfluid helium droplets provide evidence for the key role of the first helium layer surrounding the dopant molecule in determining the molecule's spectroscopic features. Recent investigations of emission spectra of phthalocyanine in helium droplets revealed a doubling of all transitions. Herein, we present the emission spectra of Mg-phthalocyanine and of phthalocyanine-argon clusters in helium droplets, which confirm the splitting as a general effect of the helium environment. A scheme of levels is deduced from the emission spectra and attributed to quantized states of the first helium layer surrounding the dopant molecule. 相似文献
In photochemical vapor deposition of aluminum film on silicon using dimethylaluminum hydride, (CH3)2AlH, a surface reaction dominated below a (CH3)2AlH pressure of 0.3 m Torr at 200°C, which was induced only with the 160 nm band emitted from a deuterium lamp. A gas-phase reaction occurred above 0.3 mTorr at 200°C, which could be induced by both 160 nm and 240 nm emission bands from the lamp. To distinguish between surface ad gas-phase reactions, a thickness profile was used. At 240°C the surface reaction could be induced even by the 240 nm band, while the deposits formed under illumination of the two bands were thinner than those obtained with only the 240 nm band, indicating occurrence of vacuum ultraviolet (VUV)-enhanced desorption. The mechanism responsible for the observed wavelength dependence in unclear. The electrical resistivity of the films deposited at 200°C was 4.5 μΩ cm, which did not change with wavelength. 相似文献
Experiments for the determination of mono-, di and tri-butyltin (MBT, DBT and TBT) by hydride generation/gas chromatography/atomic absorption spectrometry in various matrices (sediment, suspended matter, mussel, algae and water) have revealed that poor butyltin recoveries are obtained in sediments displaying high sulphur and hydrocarbon contents; very poor recoveries were also observed for TBT in sediments with high chlorophyll pigment contents as well as in algal samples. It was however not clear whether the hydride generatin was inhibited by these infering compounds, as was previously assumed in the case of hydrocarbons, or whether interferences affected the atomization rate. Further studies were performed to solve this problem in order to validate this method in the case of analyses of, for example, oil-contaminated sediment and algae. This paper presents the results obtained. It is concluded here that the poor recoveries were due to an inhibition of hydride generation rather than to interference at the atomization stage. 相似文献
A novel chemical reduction method using an activated alkaline hydride (LiH or NaH-t-BuONa) in tetrahydrofuran solvent has been applied to antimony salt reduction. X-ray diffraction and transmission electron microscopy studies have been carried out to characterize the morphology and structure of the materials. Alkali hydride nature influence has been proved. In both cases the process allows to prepare antimony particles in nanometer range from few nanometers to about 20nm which could be used as anodic materials for lithium–ion batteries. With lithium hydride well-crystallized particles inclined to agglomeration were observed whereas finely dispersed amorphous particles were pointing out after activated sodium hydride reduction. 相似文献
Conductivity of electrons in a quasi-one-dimensional (Q1D) system over liquid helium in narrow channels with the parabolic profile of the potential well has been investigated at temperature T, from 0.4 to 1.8 K, for different driving electric fields and radius of channel curvature. The interval of linear electron densities varied from 2.18×103 up to 1.7×106 cm−1.
The inverse mobility (1/μeff) in the electron-ripplon scattering region at the high linear densities of charges in the channel increases with temperature decreasing. This anomalous behavior of the electron transport in the low-temperature region has been explained by either the electron ordering or the polaronic effects in confined conducting channels. The nonlinear behavior of the electron velocity as a function of a driving electric field is supposed to be due to Breg–Cherenkov radiation of the ripplons. The radiation occurred if the velocity of electrons in the channel approaches to the critical value. 相似文献