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111.
Prof. Dr. José‐Luis M. Abboud Dr. Balázs Németh Prof. Dr. Jean‐Claude Guillemin Prof. Dr. Peeter Burk Aiko Adamson Eva Roos Nerut 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(13):3981-3991
A Fourier transform ion cyclotron resonance spectrometry (FT‐ICR) study of the gas‐phase protonation of ammonia‐borane and sixteen amine/boranes R1R2R3N? BH3 (including six compounds synthesized for the first time) has shown that, without exception, the protonation of amine/boranes leads to the formation of dihydrogen. The structural effects on the experimental energetic thresholds of this reaction were determined experimentally. The most likely intermediate and the observed final species (besides H2) are R1R2R3N? BH4+ and R1R2R3N? BH2+, respectively. Isotopic substitution allowed the reaction mechanism to be ascertained. Computational analyses ([MP2/6‐311+G(d,p)] level) of the thermodynamic stabilities of the R1R2R3N? BH3 adducts, the acidities of the proton sources required for dihydrogen formation, and the structural effects on these processes were performed. It was further found that the family of R1R2R3N? BH4+ ions is characterized by a three‐center, two‐electron bond between B and a loosely bound H2 molecule. Unexpected features of some R1R2R3N? BH4+ ions were found. This information allowed the properties of amine/boranes most suitable for dihydrogen generation and storage to be determined. 相似文献
112.
The objective was to use multiple paths through the slurry to determine the lowest concentration that provided accurate attenuation measurements and to measure the velocity of sound through an effective long path. Ultrasonic attenuation measurements were obtained for slurries of silica (10 microm diameter) in water for concentrations of 0.1%, 0.25%, 0.5%, 0.75% and 1% silica by weight. Attenuation measurements for concentrations less than 0.1% may prove useful for process control to detect contaminants. A long path is obtained due to multiple reflections occurring within the stainless steel (SS) vessel used; broad-band transducers are affixed on the outside of the thick-walled vessel. The signal in the receive transducer permits the measurement of the attenuation and also the velocity by measuring the time-of-flight. The FFT of the appropriate signal for each echo was obtained and compared with that for water to yield the attenuation as a function of frequency. The attenuation measurements are self-calibrating because they are not affected by changes in the pulser voltage. The data show the feasibility for measuring a concentration of 0.025 wt% silica, which is equivalent to 0.25 g of silica in 1 l of water. Therefore, such measurements can prove useful for detecting contaminants in liquid. The velocity of sound measurements for solutions of hydrogen peroxide in water were obtained and accurate to about 0.3m/s, or 0.02% uncertainty. 相似文献
113.
Peep Adamson 《Optics Communications》2012,285(13-14):3210-3216
The possibilities of determining the optical parameters of uniaxially anisotropic non-absorbing ultrathin films on the basis of ellipsometric parameters are analyzed in the framework of a long-wavelength approximation. It is shown that the special convenience of this analytical approach lies in the fact that it enables to find out the situations where it is possible to decouple the optical constants and the thickness (to provide correlation-free measurements) of an anisotropic ultrathin film. The accuracy of the obtained formulas for determining the parameters of ultrathin films is estimated by computer simulation of the reflection problem on the basis of the exact electromagnetic theory for anisotropic layered systems. 相似文献