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排序方式: 共有62条查询结果,搜索用时 49 毫秒
1.
Pieter E. Schipper 《Chemical physics》1976,12(1):15-23
The theory of dispersion-induced circular dichroism (the CD induced in a transition of an achiral species through long-range dispersive coupling with a chiral species) is extended to include vibronic terms. Symmetry rules are deduced for DICD-active vibronic states. It is shown that the intensity distribution over DICD-active vibrations within a given electronic band of the achiral species gives both insight into the mechanism through which the DICD appears, and vibronic spectral data not accessible through direct absorption studies. Applications to the carbonyl chromophore and comparison with recent experimental studies suggest that vibronic terms may predominate in certain cases over those expected from the purely electronic case. 相似文献
2.
P.?RudolphEmail author F.J.?Ligterink J.L.?Pedersoli Jr. M.?van Bommel J.?Bos H.A.?Aziz J.B.G.A.?Havermans H.?Scholten D.?Schipper W.?Kautek 《Applied Physics A: Materials Science & Processing》2004,79(2):181-186
Paper is one of the most important materials in cultural heritage given its extensive use as the data carrier for religious, artistic and scientific records. For both aesthetic and conservation reasons, cleaning of these materials is often needed. Current paper cleaning methods using conventional means are not always sufficient, e.g. for the local cleaning of paper in the vicinity of sensitive media. In this respect a ns-pulse laser provides a valuable tool for solving difficult cleaning problems. The influence of various laser wavelengths (355 nm, 532 nm, and 1064 nm) and the ageing status of modern paper test systems were studied. Colorimetric measurements, the determination of the average molecular mass of cellulose, and chemiluminescence analysis proved to be useful for the characterization of the laser-treated paper. Treatment with green laser light at =532 nm below the paper ablation threshold fluence gave the most promising results on pure papers, with no discolouration and no other visible alteration, nor detectable chemical changes. PACS 06.60.J; 78.60.Ps; 81.65.Cf 相似文献
3.
X-irradiation of a single crystal of 2-chloro-2,2'-spirobis(1,3,2-benzodioxaphosphole) yields the oriented PVI radical anion formed by electron capture. Directions of maximum values of the magnetic hyperfine tensors of 31P, 35Cl, and 37Cl are coincident and oriented along the P—Cl linkage, indicating an octahedral structure with the unpaired electron and chlorine in axial positions. 相似文献
4.
5.
J?RG?FELDVOSSEmail author SALVATORE?SICILIANO THOMAS?WEIGEL 《Transformation Groups》2016,21(2):377-398
In this paper it is shown that the projective cover of the trivial irreducible module of a finite-dimensional solvable restricted Lie algebra is induced from the one dimensional trivial module of a maximal torus. As a consequence, the number of the isomorphism classes of irreducible modules with a fixed p-character for a finite-dimensional solvable restricted Lie algebra L is bounded above by p MT(L), where MT(L) denotes the maximal dimension of a torus in L. Finally, it is proved that in characteristic p > 3 the projective cover of the trivial irreducible L-module is induced from the one-dimensional trivial module of a torus of maximal dimension, only if L is solvable. 相似文献
6.
The review summarizes the development of lithium ion batteries beginning with the research of the 1970–1980s which lead to modern intercalation type batteries. Following the history of lithium ion batteries, material developments are outlined with a look at cathode materials, electrolyte solutions and anode materials. Finally, with lithium sulfur and lithium oxygen batteries two post intercalation type lithium batteries are discussed. The focus of the material discussions lies on basic understanding, problems and opportunities related to the materials. 相似文献
7.
Derek J. Schipper 《Tetrahedron》2009,65(16):3155-865
Site-selective direct arylation of both sp2 and sp3 sites on azine N-oxide substrates is described. The arylation reactions are carried out in either a divergent manner or a sequential manner. The sp3 arylation reaction is applied to the synthesis of the natural products, papaverine and crykonisine, and a rationale for low reactivity of electron-deficient aryl halides is provided. Mechanistic investigations point toward the intimate involvement of the base in the mechanism of these reactions. 相似文献
8.
9.
Geoffrey S. Sinclair Robert C. M. Claridge Andrew J. Kukor W. Scott Hopkins Derek J. Schipper 《Chemical science》2021,12(6):2304
Non-covalent bonding interactions, such as chalcogen bonding, can have a substantial effect on the electronic and physical properties of conjugated polymers and is largely dependent on the strength of interaction. Functional groups that are traditionally used to instill chalcogen bonding such as alkoxy or fluorine substituents can demand challenging synthetic effort, as well as have drastic effects on the electronics of a π-system. The incorporation of a N-oxide functionality into bithiazole-containing materials, a synthetically simple transformation, has been entirely overlooked until now. A systematic analysis of the effects of N-oxidation on the electronic and physical properties of bithiazole-containing materials has been undertaken. N-Oxidation has been found to affect the electronic band gap through increase of the HOMO and lowering of the LUMO. Furthermore, exceptionally strong intramolecular S–O chalcogen bonding interactions in the bithiazole core contribute to rigidification of the conjugated system. Computational analysis of this system has shown this N-oxide chalcogen bonding interaction to be significantly stronger than other chalcogen bonding interactions commonly exploited in conjugated materials. N-Oxide incorporation into thiazole-containing conjugated materials can have substantial effects on both the electronic and physical properties. A notably strong non-covalent S–O interaction is observed between the N-oxide and neighbouring sulfur. 相似文献
10.
The possibility that the Kohn-Sham (KS) solution for a noninteracting auxiliary electron system is not the conventional one-determinantal
pure state but a few-determinantal ensemble has been investigated. The KS solutions (the exchange-correlation potential v
xc and the orbitals) have not been approximated by local-density or density-gradient approximations but have been constructed
from an accurate ab initio electron density. The lowest singlet states of the CH2 and C2 molecules have been selected for this investigation since for these cases the ground-state wave function Ψ is nondegenerate
but has an essentially multideterminantal character (electron correlation is strong). For C2 the dependence of the type of KS solution on the bond distance R(C–C) has been studied at the QZ level. For the shortest distance considered, R(C–C)=1.8 a.u., a pure-state KS solution has been obtained. For the equilibrium distance R
e(C–C)=2.348 a.u. and at larger distances ensemble solutions have been obtained with widely varying weights of the individual
determinants, depending on the bond distance. For CH2 the dependence of the type of KS solution on the basis has been studied: calculation in the triple zeta (TZ) basis for the
KS orbitals yields an ensemble solution, while the pure-state KS solution has been obtained in the quadruple zeta (QZ) basis.
The form of the KS orbitals has been compared with that of the natural orbitals (NOs). It has been shown for the model example
of the stretched H2 molecule as well as for CH2 and C2, that the KS orbitals of the pure state may be rather different from the corresponding NOs, while the occupied KS orbitals
of the ensemble solution can be considered as plausible approximations to the corresponding NOs.
Received: 10 February 1998 / Accepted: 10 June 1998 / Published online: 3 September 1998 相似文献