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排序方式: 共有483条查询结果,搜索用时 15 毫秒
1.
Q. Sun Q. Wang X.G. Gong V. Kumar Y. Kawazoe 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(1):77-81
We report results of the atomic and electronic structures of Al7C cluster using ab initio molecular dynamics with ultrasoft pseudopotentials and generalized gradient approximation. The lowest energy structure is
found to be the one in which carbon atom occupies an interstitial position in Al7 cluster. The electronic structure shows that the recent observation [Chem. Phys. Lett. 316, 31 (2000)] of magic behavior of Al7C- cluster is due to a large highest occupied and lowest unoccupied molecular orbital (HOMO-LUMO) gap which makes Al7C- chemically inert. These results have further led us to the finding of a new neutral magic cluster Al7N which has the same number of valence electrons as in Al7C- and a large HOMO-LUMO gap of 1.99 eV. Further, calculations have been carried out on (Al7N)2 to study interaction between magic clusters.
Received 28 July 2001 相似文献
2.
Hirofumi Kuroda Emi Hanaki Hironori Izawa Michiko Kano Hiromi Itahashi 《Tetrahedron》2004,60(8):1913-1920
α-Vinylfurans were obtained by phosphine-initiated cyclization of various enynes bearing a carbonyl group at the ene end in the presence of various aldehydes, in moderate to high yields. The reaction may consist of 1,6-addition of phosphine to the enynes, ring closure, and Wittig reaction between the ylid resulting from cyclization and an aldehyde. Thus, various aldehydes were able to be used in the reaction. The reaction was influenced greatly by the substituents at the acetylene position (R1) and the α-position of the carbonyl group (R3). 相似文献
3.
Michiko Tamura 《Geometriae Dedicata》1992,42(3):311-315
LetM be a complete smooth surface of constant mean curvature in the Euclidean 3-space. If there exists two helical geodesics onM through each point ofM, thenM is either a plane, a sphere, or a circular cylinder. 相似文献
4.
5.
Hiromi Matsuhashi Masakazu Oikawa Hiromi Shibata Michiko Tanaka 《Reaction Kinetics and Catalysis Letters》1998,65(2):253-258
Reversible formation of F+-centers was observed over platinum promoted sulfated zirconia in the presence and absence of hydrogen. The intensity of ESR
signal of F+-centers was increased by treatment in He stream and it was decreased rapidly by supply of hydrogen in gas phase. This behavior
seems to be related to proton spillover. 相似文献
6.
Itoh T Nagata K Yokoya M Miyazaki M Kameoka K Nakamura S Ohsawa A 《Chemical & pharmaceutical bulletin》2003,51(8):951-955
Chiral 1-substituted isoquinoline derivatives, which were obtained by the reaction using alanine derivatives as chiral auxiliaries, were transformed to (S)-2,3,9,10,11-pentamethoxyhomoprotoberberine (7) and a synthetic intermediate for O-methylkreysigine (9) in good yields and high stereoselectivity. The corresponding chiral allyl derivative of isoquinoline was transformed to a pyrrolidinoisoquinoline (16) in a highly enantioselective manner. 相似文献
7.
Keivan Esfarjani Yuichi Hashi Satoshi Itoh Sigeo Ihara Yoshiyuki Kawazoe 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1997,41(1):73-76
To study the thermodynamic and mechanical stability of toroidal isomers of C 240, we use a semi-empirical tight-binding theory and calculate their electronic structure, cohesive energy and vibrational spectra within the harmonic approximation. From these, we deduce their free energy at temperatures up to 1500K. The results are also compared to the isomer with icosahedral symmetry. Finally, we discuss within this approach, their stability and abundance. 相似文献
8.
Sasaki M Kawanishi E Nakai Y Matsumoto T Yamaguchi K Takeda K 《The Journal of organic chemistry》2003,68(24):9330-9339
Metalated O-silyl cyanohydrins of beta-silyl-alpha,beta-epoxyaldehyde have been found to serve as functionalized homoenolate equivalents by a tandem sequence involving base-promoted ring opening of the epoxide, Brook rearrangement, and alkylation of the resulting allylic anion. On the basis of mechanistic studies involving competitive experiments using the diastereomeric cyanohydrins, we propose a reaction pathway involving a silicate intermediate 36 formed by a concerted process via an anti-opening of the epoxide followed by the formation of an O-Si bond. 相似文献
9.
Sahara R Ichikawa H Mizuseki H Ohno K Kubo H Kawazoe Y 《The Journal of chemical physics》2004,120(19):9297-9301
A Monte Carlo simulation is carried out to study thermodynamic properties of Cu-Au alloys using a face-centered-cubic (fcc) lattice-gas model. To obtain quantitatively accurate results, a Finnis-Sinclair-type potential, which has been widely used for molecular dynamics (MD) simulations, is employed. To overcome some shortcomings of lattice-gas models such as neglecting vibrational entropy, the potential is mapped onto the fcc lattice using the renormalization technique. The renormalized potential gives an improved Cu-Au phase diagram compared to the original MD potential applied directly on the lattice. 相似文献
10.
The direct coupling of in-tube solid-phase microextraction (in-tube SPME) with microcolumn liquid chromatography (micro-LC) has been investigated for the analysis of antidepressants in human urine. The use of in-tube SPME has been clearly shown to be advantageous for the on-line coupling of the SPME method, as the sample pretreatment technique, with micro-LC as the separation technique. This is because much smaller amounts of the sample solutions, desorption solvents and the mobile phase are required compared with conventional SPME-LC systems. The parameters for preconcentration have been investigated for the extraction capillary with the newly developed 'wire-in-tube' configuration. 相似文献