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121.
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Robert K. Boeckman David M. Blum Edward V. Arnold Jon Clardy 《Tetrahedron letters》1979,20(48):4609-4612
The complete structure of the unique tricyclic sesterterpene gascardic acid is proposed based on a single crystal x-ray diffraction analysis of the dicyclohexylammonium salt. 相似文献
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Accurate electrolysis current integration is required in controlled-potential coulometry. Analog integrators have been shown to deviate from ideal response by as much as —0.1%. A digital integrator was designed to optimize the linearity of the voltage-to-frequency converter used, minimize the effects of temperature, eliminate integration errors caused by small polarity changes and signal noise, and allow interchangeability with an analog integrator in a state-of-the-art coulometer widely used throughout the nuclear field for controlled-potential coulometry. Evaluation of the digital integrator, calibrated versus the Faraday, showed bias-free determinations of plutonium with a relative standard deviation of approximately 0.02%. The integrator was designed specifically for use in the controlled-potential coulometric determination of plutonium, but many of the features incorporated can be adopted to digital integrators for other uses where accurate integration over long periods of time is required. 相似文献
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The HF dimer is believed to exhibit an internal rotation tunneling process between two planar but nonlinear equilibrium configurations, during which tunneling the roles of the hydrogen-bonded and the free hydrogen atom are interchanged. This process can be represented schematically with labeled atoms as HlFaH2Fb ? FaHlFbH2, and gives rise to a permutation-inversion group G4 containing four operations. In the present work the vibration-rotation-tunneling problem in (HF)2 is treated group theoretically in three ways: (i) by allowing tunneling only through a trans planar C2h intermediate, (ii) by allowing tunneling only through a cis planar C2v intermediate, and (iii) by considering the trans and cis tunneling processes both to occur, though not necessarily with the same probability. The molecular symmetry groups used for these treatments are (i) the point group C2h, (ii) the point group C2v, and (iii) a double group, which might be thought of as . Nonplanar tunneling paths are not considered, since the internal axis method (IAM) coordinate system used here cannot easily be adapted to nonplanar internal rotation motions in this molecule. Various-details of energy level diagrams, symmetry species for operators, selection rules for spectroscopic transitions, and statistical weights are presented for the (HF)2 tunneling problem, as well as some speculation on the general question of when point groups, permutation-inversion groups, or double groups are preferable for treating large-amplitude vibrational motion problems. 相似文献
128.
Kevin G. Michlewicz John J. Urh Jon W. Carnahan 《Spectrochimica Acta Part B: Atomic Spectroscopy》1985,40(3):493-499
A microwave induced plasma system capable of maintaining stable plasmas of each of the gases helium, argon, nitrogen and air is presented. The system is capable of operation at powers of up to 500 W. The TM010 cavity design is similar to that previously described in the literature with some modifications. A demountable torch facilitates centering of diffuse plasmas of helium, nitrogen and air by providing 6 flows directed tangentially within the quartz tube. This torch was not useful for argon plasmas. Toroidal argon plasmas were maintained with a threaded quartz tube arrangement. The heat generated by these plasmas was dissipated by an outer sheath of coolant air. Details of the design and preliminary characterization of each plasma system is presented. 相似文献
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Because of the extravagant claims made for the usefulness of non-flame atomic absorption spectroscopy, a critical evaluation of its performance in heavy matrix solutions, for selected trace heavy metals, was made. Studies of physical and chemical interference problems are presented for a range of inorganic and organic matrices. Often quoted remedies (e.g. selective volatilization, standard addition etc.) for solution of the more serious problems were found to be of little help in most cases. The influence of variables such as nature and flow rate of purge gas, ashing temperature and atomization temperature are also evaluated. Analyses for Cd, Cu, Pb, Zn, Ni, Co were done on samples by flame and nonflame methods in high solids solutions. While there appears to be an advantage to the non-flame method in dealing with sample solutions of high organic content, no advantage is apparent for either technique with highly inorganic matrices. 相似文献