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排序方式: 共有133条查询结果,搜索用时 15 毫秒
1.
The millimeter wave spectrum of the isotopically substituted CO dimer, (13C16O)2, has been studied for the first time, confirming and extending a recent infrared study. Eighty-seven transitions in the 77-180 GHz region have been assigned and analyzed in terms of a model-independent term value scheme involving 57 rotational levels with J=0-8. The levels can be classified into 7 “stacks” which have symmetry classifications of either A−/B+ or A+/B− and K-values of either 0 or 1. For the normal isotope, symmetry and nuclear spin statistics cause alternate rotational levels to be missing, but for (13C16O)2 all levels are present with an intensity alternation of 1:3 between A and B symmetries. The four A−/B+ stacks have not previously been observed, and the lowest of them establishes the tunneling splitting of (13C16O)2 to be 3.769 cm−1, slightly larger than the (12C16O)2 value of 3.731 cm−1. A large amount of precise experimental data is now available for the CO dimer, which should lead to greater theoretical insight into its structure and tunneling dynamics. 相似文献
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SOLIMAN A.Y. BAKEER H.M. ATTIA LA.Science Department Faculty of Teachers P.O.Box Alhasa Saudi Arabia Chemistry Department Faculty of Science Fayoum Cairo University EgyptFaculty of Engineering Ain Shames University Egypt 《中国化学》1996,14(6):532-540
3-(4-Phenyl) benzoyl propionic acid was used as the starting material for the synthesisof furanones (2), pyrrolinones (5), pyridazinones (7), benzoxazinones (8) and quinazolinones (9-11). The behaviour of the derivatives of furanones and benzoxazinones toward different nucleophiles is reported. 相似文献
4.
MENG Jian REN Yu-Fang LI Xiao-GuangLaboratory of Rare Earth Chemistry Physics Changchun Institute of Applied Chemistry Chinese Academy of Sciences Changchun Jilin ChinaPopov V.V. Repin S.M. Smirnov LA. loffe Physicotechnical Institute Russian Academy of Sciences Saint Petersburg Russia 《中国化学》1994,12(5):419-424
YBa2Cu3-xVxO7-y(x=0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6) superconductors have been prepared. X-ray diffraction shows that the system remains orthorhombic for all compositions studied, but for x > 0.4 V2O5 was detected as an impurity phase. Substitution of V5+ for Cu2+ occurs in the Cu(2) sites on the Cu(2)-O planes. The introduction of the high valence element, vanadium, produces the extra free-electrons. These electrons recombine with the positive carrier of the system. It makes depression of the mobility and the Hall number of YBa2Cu3-xVxO7-v and also results in a depression of TC. 相似文献
5.
MARIAN ELBANOWSKI MARIA PAETZ JANUSZ SIAWINSKI LESZEK CIELA 《Photochemistry and photobiology》1988,47(3):463-466
Abstract— Chemiluminescence of the Eu(II)/Eu(III)-adenine nucleotide-H2 O2 system and fluorescence of the Eu(III)-adenosine triphosphate system have been investigated. The spectral distribution of the chemiluminescence emission has shown an occurrence of three main bands (Λ=470–480,590–620 and ca. 700 nm). The energy transfer process from the adenosine triphosphate molecules to the Eu(III) ions has been observed in the fluorescence spectrum. The examined chemiluminescence and fluorescence spectra show that these both kinds of emission originate from the 5 D *** τ7 F*** ( n =1–4) transitions in the Eu(III) ions. 相似文献
6.
针对纤维材料变温环境力学性能测试的需要,在华中科技大学研制的纤维材料试验机的基础上引入了温控装置,从而实现纤维材料在高低温环境下的力学性能测试。采用该装置对不同直径微米铜丝在不同温度、不同拉伸速率条件下的力学性能开展实验研究,测试结果表明弹性模量和抗拉强度随温度的降低而线性增加,屈服强度的变化不太明显。另外,低温环境下微米铜丝的力学性能表现出与其直径相关的尺度效应,而这一现象在常温下一直没有观测到。最后,还研究了拉伸速率对微米铜丝的力学性能影响,结果表明,在现有装置的许用范围之内,拉伸速率对其力学性能的影响不大。 相似文献
7.
Jian TangA.R.W. McKellar L.A. Surin D.N. Fourzikov B.S. DumeshG. Winnewisser 《Journal of Molecular Spectroscopy》2002,214(1):87-93
The millimeter-wave spectrum of the normal isotope of the CO dimer, (12C16O)2, has been systematically surveyed in the regions 75-105 and 131-174 GHz, with additional measurements covering the entire 60-176 GHz range. By combining these results and using the technique of combination differences based on previously known energy levels, 14 new rotational levels have been assigned and precisely (≈0.1 MHz) located. They belong to 3 completely new states, 1 with A+ symmetry and 2 with A− symmetry. The position of the lowest energy A− state results in a new and lower value for the effective tunneling splitting of the CO dimer, 3.73 cm−1. The observation of dramatically different intensities for different bands supports the concept of two isomeric forms for (CO)2, the ground state having a larger intermolecular separation (≈4.4 Å) with most likely a C-bonded configuration, and the low-lying (0.88 cm−1) excited state having a smaller separation (≈4.0 Å) and an O-bonded geometry. 相似文献
8.
The present state of research on the CO dimer is reviewed. In recent years, both infrared and millimeter-wave spectra have been measured and partially assigned by the use of combination differences. A microwave-millimeter wave double resonance experiment, reported here for the first time, provides independent confirmation of these assignments and the resulting (CO)2 energy level scheme. In the double resonance experiment, the OROTRON spectrometer functions as a supersensitive intra-cavity millimeter-wave detector. We update the continuing, but difficult, experimental efforts in recording the spectra, the quest for secure assignments, and the construction of a consistent and reliable energy level scheme. Although at present we have only limited knowledge of some aspects of the CO dimer, such as its geometrical structure, we have succeeded in characterizing unambiguously nine “stacks” of ground state energy levels with “microwave accuracy” (∼0.1 MHz). Every energy level within a given stack exhibits the same symmetry: either A− or A+. Only transitions between A+ and A− levels are allowed, and consequently ordinary pure rotational transitions within a stack are forbidden. Transitions between stacks can be thought of as tunneling transitions, and the separation of the lowest energy A+ and A− states corresponds to a value of for the effective “tunneling splitting” of the CO dimer. The stacks tend to fall into two groups, corresponding to “isomers” with effective inter-molecular separations of either 4.0 or 4.4 Å. The larger inter-molecular separation of the true ground state (4.4 Å) likely corresponds to a C-bonded configuration, while the low-lying excited state with the smaller separation (4.0 Å) likely displays an O-bonded geometry. 相似文献
9.
O. B. Pavlova-Verevkina L. A. Ozerina E. D. Politova N. M. Surin A. N. Ozerin 《Colloid Journal》2009,71(4):529-533
We studied the slow aggregation of dilute TiO2 hydrosols containing narrow fractions of nanocrystals separated from polydisperse sol by the stepwise coagulation with portions of HCl. It is shown that the kinetics of this process and the structure of formed aggregates greatly depend on the ionic strength and the pH of a medium. It is suggested that, in the presence of various electrolytes, the aggregation proceeds by an identical mechanism. In this case, highly ordered aggregates are formed in which there are thin layers of medium between TiO2 nanocrystals. 相似文献
10.
Achasov M. N. Barnyakov A. Yu. Baykov A. A. Beloborodov K. I. Berdyugin A. V. Bogdanchikov A. G. Botov A. A. Golubev V. B. Dimova T. V. Druzhinin V. P. Zhabin V. N. Kardapoltsev L. V. Kovrizhin D. P. Korol A. A. Kupich A. S. Martin K. A. Melnikova N. A. Muchnoi N. Yu. Obrazovsky A. E. Pakhtusova E. V. Pugachev K. V. Savchenko Ya. S. Serednyakov S. I. Silagadze Z. K. Surin I. K. Usov Yu. V. Kharlamov A. G. Shtol D. A. 《Physics of Atomic Nuclei》2021,84(2):197-200
Physics of Atomic Nuclei - The process $$e^{+}e^{-}\to\eta\pi^{0}\gamma$$ is studied in the range of center-of-mass (c.m.) collision energies between 1.05 and 2.00 GeV on the basis of data... 相似文献