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41.
A simple electrostatic analysis is given of the virtual charge (solvaton) model to represent the environment effect on the electronic wave function of a solute immersed in a polarizable surrounding. New features of this model are found. The classical aspects are discussed and secondly the quantal implications are considered. A correct Hartree-Fock-like operator is derived which represents an electron in a molecular orbital subjected to the average effect of the other electrons and to the reaction field produced by the virtual charges on the atomic centers.A general formalism based on the preceding model is presented in appendix. The final equations have a form similar to Newton's equation to represent a solvated electron. Unlike some other theories in this field, there is no cut-off involved in the evaluation of the molecular integrals. 相似文献
42.
M. Matschke 《Tetrahedron letters》2005,46(47):8249-8251
Syntheses and redox chemistry of the nearly unknown 4,4′,5,5′-tetraamino derivatives of 2,2′-biimidazole are studied. These cyclic versions of electron-rich ethenes are only stable under strictly anaerobic conditions. In the presence of oxygen, a fast oxidation reaction occurs to form stable, deeply coloured tetraazafulvalenes. Leuco-forms, however, can be stabilized towards air by acylation reactions. This accounts for the hexa-Boc derivative 6. Based on these findings, we present the first synthesis of tetraazafulvalenes, which possess four peripheric secondary amine functions. 相似文献
43.
44.
The relations between the Hellmann-Feynman forces in laboratory fixed (L-) and relative (R-) coordinate systems are clarified. In the usualL-coordinate system, the force is interpreted as force on nucleus, while in theR-coordinate system, it means force on whole particles consisting of the electrons and nuclei of each interacting subsystem. From a perturbation theoretical viewpoint, the concept of the force on whole particles correctly corresponds to the perturbation energy and is superior to the force on the nucleus. 相似文献
45.
Euan J. Squires 《Foundations of Physics Letters》1995,8(6):589-591
An experiment to test a possible explanation of the Schmidt backwards causation results is suggested. The experiment might distinguish between many- and one- world interpretations of quantum theory. 相似文献
46.
C. David Levermore 《Journal of statistical physics》1996,83(5-6):1021-1065
This paper presents a systematicnonperturbative derivation of a hierarchy of closed systems of moment equations corresponding to any classical kinetic theory. The first member of the hierarchy is the Euler system, which is based on Maxwellian velocity distributions, while the second member is based on nonisotropic Gaussian velocity distributions. The closure proceeds in two steps. The first ensures that every member of the hierarchy is hyperbolic, has an entropy, and formally recovers the Euler limit. The second involves modifying the collisional terms so that members of the hierarchy beyound the second also recover the correct Navier-Stokes behavior. This is achieved through the introduction of a generalization of the BGK collision operator. The simplest such system in three spatial dimensions is a 14-moment closure, which also recovers the behavior of the Grad 13-moment system when the velocity distributions lie near local Maxwellians. The closure procedure can be applied to a general class of kinetic theories. 相似文献
47.
48.
Christian Remling 《Proceedings of the American Mathematical Society》1996,124(7):2097-2100
In 1949, Hartman and Wintner showed that if the eigenvalue equations of a one-dimensional Schrödinger operator possess square integrable solutions, then the essential spectrum is nowhere dense. Furthermore, they conjectured that this statement could be improved and that under this condition the essential spectrum might always be void. This is shown to be false. It is proved that, on the contrary, every closed, nowhere dense set does occur as the essential spectrum of Schrödinger operators which satisfy the condition of existence of -solutions. The proof of this theorem is based on inverse spectral theory.
49.
It has been shown that the “internal” isotope distribution within a given molecular species at the natural abundance level is accessible by a new method, SNIF-NMR, which is based on deuterium NMR. Relative internal factors, Ri/j,have been defined which enable the isotope content of a given site, i, to be compared to that of another molecular site, j, taken as the reference. Several referencing methods intended to provide direct access to relative , Ti , and , (D/H)i , site-specific parameters, are now discussed from both the theoretical and the experimental points of view. In the , which involves a time-consuming chemical transformation of the sample, the risk exists of more or leas systematic errors resulting from discriminating fractionation effects. However this technique offers, conversely, an interesting way of investigating kinetic isotope effects without the need for specific labelling. In spite of its lower spectral precision the has the advantage of being fast and less sensitive to systematic errois and may be used for direct rough routine determinations of the site-specific isotope contents. More precise results can be obtained, at the price of contaminating the sample, when an is added and signal heights are used, remembering however that the intensity parameters then have no strict physical meaning in terms of absolute isotope contents. The site-specific parameters, Ti and (D/H)i thus accessible, provide new information on the mechanisms of the fractionation effects occurring in natural conditions and examples are considered. 相似文献
50.
A novel Ugi-five-centre-four-component reaction (U-5C-4CR) of aldehydes, primary amines, trimethylsilylazide and 2-isocyanoethyltosylate yielding tetrazolopiperazine building blocks is described. 相似文献