共查询到20条相似文献,搜索用时 109 毫秒
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胞嘧啶与一氧化碳复合物的结构与性质 总被引:1,自引:0,他引:1
在B3LYP/6-311+G**水平上对胞嘧啶…CO复合物体系进行了理论计算, 发现了6个能量极小的复合物. 其结合方式是CO的C或O原子与胞嘧啶的N—H键形成氢键, 最稳定的复合物的结合能为-8.72 kJ·mol-1. CO的C原子与胞嘧啶的结合具有更强的优势, C原子结合的复合物中CO的键长缩短, 而O结合的复合物中CO键长伸长. 同时, 对复合物的振动分析发现, 在C原子结合的复合物中CO的伸缩频率蓝移, 而O结合的复合物中CO伸缩频率是红移的. 相似文献
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介绍黎明职业大学高分子材料加工技术专业的核心课程《高分子材料分析与测试》的课程设计和教学改革的做法。课程以实现学生向"准员工"的转变为教学目标。通过对行业企业进行调研,确定该课程的对接岗位为质量检验岗位,工作内容为化验、质检和品管,基于岗位工作内容进行课程设计。采用项目化方式,三个工作内容分别对应以典型方法、典型产品和典型常识为项目进行模块设计。以模块任务为中心,将教师的"讲"与学生的"练"有机结合起来,综合应用提倡学生互教的交互培训法、引导学生自主学习的主题探究法、锻炼学生专业素质的四阶段技能训练法等教学方法。 相似文献
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颜欣欣 《广东微量元素科学》2010,17(5):63-63
自从1955年科学家们发现了芬芳糖耐量因子(GTF),并证实了(GTF)具有生物活性的重要结构成分是三价铬后,铬及其所有化合物的生物学功能受到了科学家们广泛的重视,如运用于保健品、强化食品、营养补充利中、富集蔬菜和富集茶叶中等等。 相似文献
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催化技术在现代工业生产和日常生活中发挥着举足轻重的作用,开发高效的催化剂是催化领域重要的研究方向。近些年来,许多研究发现催化剂的缺陷对其催化活性有着重要的影响,同时各种各样的缺陷催化剂也被开发出来。尽管如此,缺陷与催化活性之间的关系仍有待厘清。本文围绕这一主题,分别介绍了固体缺陷化学的基础、催化剂中缺陷的类型、表征、可控构筑以及在催化中的作用和动态变化,最后进行总结和展望。希望通过本文阐明催化剂缺陷化学研究的起源与发展,强调缺陷对催化的重要性,为今后高效催化剂的进一步开发与机理研究提供指导。 相似文献
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L. Kövér 《Surface and interface analysis : SIA》2007,39(6):556-558
ISO/TR 18394 provides guidance for the identification of chemical effects on x‐ray or electron‐excited Auger electron spectra as well as for applications of these effects in chemical characterization of surface/interface layers of solids. In addition to elemental composition, information can be obtained on the chemical state and the surrounding local electronic structure of the atom with the initial core hole from the changes of Auger electron spectra upon the alteration of its local environment. The methods of identification and use of chemical effects on Auger electron spectra, as described in this Technical Report, are very important for accurate quantitative applications of Auger electron spectroscopy. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
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《Chemical physics letters》1986,124(2):181-186
Quantum-mechanical calculations on a realistic system show that excitation of a local mode may be accomplished by using two lasers. More importantly, this local mode does not decay into the bath modes of the molecule even at very long times. This excitation is accomplished using two lasers tuned to two eigenstates whose wavefunctions interfere to give the local excitation. Most significantly, this observation for a model system implies that mode specific control of chemical reactions may be accomplished using two lasers to excite two overtone transitions. 相似文献
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Information on the electronic structure of a molecule and its chemical bonds is encoded in the molecular normal vibrational modes. However, normal vibrational modes result from a coupling of local vibrational modes, which means that only the latter can provide detailed insight into bonding and other structural features. In this work, it is proven that the adiabatic internal coordinate vibrational modes of Konkoli and Cremer [Int. J. Quantum Chem. 67, 29 (1998)] represent a unique set of local modes that is directly related to the normal vibrational modes. The missing link between these two sets of modes are the compliance constants of Decius, which turn out to be the reciprocals of the local mode force constants of Konkoli and Cremer. Using the compliance constants matrix, the local mode frequencies of any molecule can be converted into its normal mode frequencies with the help of an adiabatic connection scheme that defines the coupling of the local modes in terms of coupling frequencies and reveals how avoided crossings between the local modes lead to changes in the character of the normal modes. 相似文献
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Borgwarth K Ricken C Ebling DG Heinze J 《Analytical and bioanalytical chemistry》1996,356(3-4):288-294
Resolution studies of scanning electrochemical microscopy (SECM) have been performed in the feedback mode and in the generator/collector mode at circular model structures. A quantitative correlation of the loss in resolution and the increase in distance between tip and sample is found. Measuring a band electrode of just 500 nm width, the high sensitivity of the SECM in identifying chemically active sites is proven. Applied to polymer samples, the chemical composition was determined in the feedback mode at high lateral resolution. The difference in electrical conductivity allows one to distinguish between doped and undoped parts of a polyaniline film. By scanning above a blend consisting of polypyrrole and polypropylene, a map of the local chemical composition was obtained. In this context, the influence of the tip overpotential on the image is discussed. 相似文献
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Paredes JI Gracia M Martínez-Alonso A Tascón JM 《Journal of colloid and interface science》2005,288(1):190-199
Scanning tunneling microscopy (STM) and noncontact tapping mode atomic force microscopy (AFM) have been employed to study on a local scale the structural and, for the first time, the chemical changes of carbon black (CB) particles following plasma oxidation. STM imaging of the pristine, untreated particles revealed a relatively ordered structure of tiny crystallites with a few amorphous regions. After plasma treatment, the crystallites were no longer observed and the CB particle surface exhibited a noticeable and ubiquitous increase in atomic-scale disorder. Phase contrast images obtained with noncontact tapping mode AFM indicated that the untreated CB particles were essentially hydrophobic as a pristine basal surface of graphite, but with occasional hydrophilic patches. By contrast, their plasma-treated counterparts displayed enhanced hydrophilicity as a result of the introduction of oxygen onto the CB surface, the presence of which was evidenced by X-ray photoelectron spectroscopy, but most significantly, such enhancement was observed to be quite uniform at a local scale of individual particles. The possibility of investigating on a very local scale the chemical behavior of oxidized CB particles should be useful for the control and optimization of their dispersion properties in different systems. 相似文献
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This review article considers the origin of vibrational anharmonicity in molecules, and the effects that vibrational resonances have on the anharmonicity constants which may be extracted from spectroscopic observations. The importance of the effects of Darling—Dennison resonances, which increase with increasing excitation, as well as Fermi resonances, are considered. The local mode approach to X—Y stretching vibrations is dealt with, as a means of simultaneously accounting for Darling—Dennison resonances and of inter-relating normal mode stretching anharmonicity constants, thus reducing the number of parameters to be determined. The inclusion of Fermi resonances, as necessary, into the calculation is next considered, and the joint local mode-normal mode analysis explained.Applications to ethylenic and methyl group molecules are made. The success of the analyses is demonstrated through complete sets of physically representative anharmonicity constants which reproduce vibrational observations into the visible (16 500 cm−1), and which are mutually self-consistent over molecules containing the same functional groups.Extensions of the simple local mode model are considered, as means of achieving anharmonicity parameters which should describe more closely the molecular potential energy surface, and hence the concomitant physical and chemical processes which it controls. 相似文献