共查询到20条相似文献，搜索用时 15 毫秒
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刘凤丽 《东北林业大学学报》2005,33(6):114-115
使用相对论与非相对论赝势,在HF、B3LYP水平上详细研究了电子相关效应和相,謦誉謦尊CuIn分子平衡几何构型和能量的影响。结果显示,电子相关效应缩短核间距,提高振动频率,降低能量;相对论效应加强了它的强度,使CuIn分子更加稳定。同时,在B3LYP水平上采用相对论有效核芯势（RCEP）进行能量扫描得型了CuIn分子势能曲线,给出CuIn分子的力参数和光谱数据。计算结果显示,得到的Culn分子基态平衡几何、振动频率、解离能等与可得到的试验结果吻合。 相似文献
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Rotational spectra have traditionally been measured without a concurrent means of differentiating the molecular constituents of the sample. Here, we present an all-optical multipulse experiment that allows the correlated measurement of rotational and mass or photoelectron spectra by combining Fourier transform rotational coherence spectroscopy with resonance-enhanced multiphoton ionization. We demonstrate the power of this method with the determination of ground-state rotational constants and fragmentation channels for 10 different isotopes in a natural carbon disulfide sample. Three of the reported rotational constants were previously inaccessible by conventional spectroscopic techniques. 相似文献
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Aluminas and their surface chemistry play a vital role in many areas of modern technology. The behavior of adsorbed water is particularly important and poorly understood. Simulations of hydrated alpha-alumina (0001) surfaces with ab initio molecular dynamics elucidate many aspects of this problem, especially the complex dynamics of water dissociation and related surface reactions. At low water coverage, free energy profiles established that molecularly adsorbed water is metastable and dissociates readily, even in the absence of defects, by a kinetically preferred pathway. Observations at higher water coverage revealed rapid dissociation and unanticipated collective effects, including water-catalyzed dissociation and proton transfer reactions between adsorbed water and hydroxide. The results provide a consistent interpretation of the measured coverage dependence of water heats of adsorption, hydroxyl vibrational spectra, and other experiments. 相似文献
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Ultrasonic irradiation of liquids causes acoustic cavitation: the formation, growth, and implosive collapse of bubbles. Bubble collapse during cavitation generates transient hot spots responsible for high-energy chemistry and emission of light. Determination of the temperatures reached in a cavitating bubble has remained a difficult experimental problem. As a spectroscopic probe of the cavitation event, sonoluminescence provides a solution. Sonoluminescence spectra from silicone oil were reported and analyzed. The observed emission came from excited state C(2) (Swan band transitions, d(3)IIg-a(3)II(micro)), which has been modeled with synthetic spectra as a function of rotational and vibrational temperatures. From comparison of synthetic to observed spectra, the effective cavitation temperature was found to be 5075 +/- 156 K. 相似文献
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The dynamics of the carbonium ion (CH(5)(+)), a highly reactive intermediate with no equilibrium structure, was studied by measuring the infrared spectra for internally cold CH(5)(+)(H(2))n(n = 1, 2, 3) stored in an ion trap. First-principle molecular dynamics methods were used to directly simulate the internal motion for these ionic complexes. The combined experimental and theoretical efforts substantiated the anticipated scrambling motion in the CH(5)(+) core and revealed the effect of the solvent molecular hydrogen in slowing down the scrambling. The results indicate the feasibility of using solvent molecules to stabilize the floppy CH(5)(+) ion in order to make it amenable to spectroscopic study. 相似文献
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Primary sequence information from intact proteins by electrospray ionization tandem mass spectrometry 总被引：6，自引：0，他引：6
Tandem mass spectrometry has been used to obtain information related to portions of the primary sequence for an intact protein, bovine ribonuclease A. Multiply charged molecular ions, generated by electrospray ionization, were collisionally dissociated at low energies in a triple quadrupole mass spectrometer to yield singly and multiply charged fragment ions that can be assigned to the known sequence of the protein. Dissociation of the highly charged molecular ions resulted in pairs of complementary product ions. The higher order (gas-phase) protein structure affects the dissociation processes, as observed in comparisons of tandem mass spectra of the native and disulfide-reduced forms of ribonuclease A. 相似文献
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The compelling need for standoff detection of hazardous gases and vapor indicators of explosives has motivated the development of a remotely pumped, high-gain air laser that produces lasing in the backward direction and can sample the air as the beam returns. We demonstrate that high gain can be achieved in the near-infrared region by pumping with a focused ultraviolet laser. The pumping mechanism is simultaneous resonant two-photon dissociation of molecular oxygen and resonant two-photon pumping of the atomic oxygen fragments. The high gain from the millimeter-length focal zone leads to equally strong lasing in the forward and backward directions. Further backward amplification is achieved with the use of earlier laser spark dissociation. Low-divergence backward air lasing provides possibilities for remote detection. 相似文献
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Variation in spectral characteristics of dissolved organic matter derived from rape straw of plants grown in Se-amended soil 
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下载免费PDF全文 JIA Wei ZHAO Xiao-hu ZHAO Yuan-yuan XU Jia-yang MING Jia-jia CAI Miao-miao HU Cheng-xiao 《农业科学学报》2020,19(7):1876-1884
Straw return is an effective management practice. It not only utilizes agricultural waste but also introduces dissolved organic matter(DOM) into the soil. Selenium(Se) is an essential trace element in the human diet and contributes to the popularity of Se-enriched agricultural products in the Chinese market. Moreover, there are still some Se-enriched agricultural products that have yet to be utilized. This study investigated whether Se addition in soil caused component changes in the DOM extracted from rape straw. DOM extracted from rape straw grown in soil with four Se levels(0, 0.1, 0.5 and 1.0 mg Se kg–1 soil) was characterized by UV-Visible spectroscopy, fluorescence spectroscopy and FTIR spectroscopy. The UVvisible spectra revealed that 0.1 mg Se kg–1 soil reduced the molecular weight of DOM and caused the presence of more irreplaceable aromatic structures in the substituent groups of the DOM, while 0.5 and 1.0 mg Se kg–1 soil only reduced the DOM molecular weight. Fluorescence spectroscopy indicated that Se improved the humification degree but reduced the aromaticity of DOM. FTIR spectra proved that Se altered the contents of carboxylic acids, amino acids, alcohols and aromatic heterocycles in DOM, which were maximized in the 0.5 and 1.0 mg Se kg–1 treatment groups. We concluded that Se application could change the composition of DOM extracted from rape straw, potentially impacting the nutrient bioavailability in soil. This study provides basic data on Se-enriched rape straw utilization for eco-agriculture. 相似文献
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Rak A Pylypenko O Durek T Watzke A Kushnir S Brunsveld L Waldmann H Goody RS Alexandrov K 《Science (New York, N.Y.)》2003,302(5645):646-650
Rab/Ypt guanosine triphosphatases (GTPases) represent a family of key membrane traffic regulators in eukaryotic cells whose function is governed by the guanosine diphosphate (GDP) dissociation inhibitor (RabGDI). Using a combination of chemical synthesis and protein engineering, we generated and crystallized the monoprenylated Ypt1:RabGDI complex. The structure of the complex was solved to 1.5 angstrom resolution and provides a structural basis for the ability of RabGDI to inhibit the release of nucleotide by Rab proteins. Isoprenoid binding requires a conformational change that opens a cavity in the hydrophobic core of its domain II. Analysis of the structure provides a molecular basis for understanding a RabGDI mutant that causes mental retardation in humans. 相似文献
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腐殖质是一类具有复杂结构的大分子有机化合物,广泛参与各种地球化学循环,并在工农业生产中扮演着及其重要的地位。因此,腐殖质的研究一直是学界关注的重点。近年来,光谱学技术的飞速发展为腐殖质化学的研究提供了有效的研究手段,特别是红外吸收光谱(IR)、核磁共振谱(NMR)、荧光光谱、紫外/可见光谱(UV/vis)、电子顺磁共振谱(EPR)等技术的运用,使得人们对于腐殖质的结构特征、反应机理都有了进一步的认识。综述了腐殖质化学的光谱学最新研究进展,为今后腐殖质化学研究及其在环境污染防治中的应用提供了参考。 相似文献
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Adhesion of a biological cell to another cell or the extracellular matrix involves complex couplings between cell biochemistry, structural mechanics, and surface bonding. The interactions are dynamic and act through association and dissociation of bonds between very large molecules at rates that change considerably under stress. Combining molecular cell biology with single-molecule force spectroscopy provides a powerful tool for exploring the complexity of cell adhesion, that is, how cell signaling processes strengthen adhesion bonds and how forces applied to cell-surface bonds act on intracellular sites to catalyze chemical processes or switch molecular interactions on and off. Probing adhesion receptors on strategically engineered cells with force during functional stimulation can reveal key nodes of communication between the mechanical and chemical circuitry of a cell. 相似文献
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不同花色菊花品种花色素成分的初步分析 总被引：32，自引：0，他引：32
为了分析形成菊花花色的色素成分以搞清楚花色形成的机理,该文对17个菊花品种的花瓣进行了花色表型测定、特征显色反应和紫外 可见光谱扫描分析.结果发现:菊花不同花色（黄色、白色、红色、紫色和橙色）品种的色素由类黄酮和类胡萝卜素两大类组成.黄色花主要含有类胡萝卜素和黄酮类化合物;白色花仅含有黄酮类化合物;红色和紫色花主要由花色素苷和黄酮类化合物组成;橙色花的色素包括类胡萝卜素、黄酮类化合物和花色素苷.该项研究为菊花花色素成分的进一步分离和鉴定等工作奠定了基础,同时也为菊花花色的分子育种提供帮助. 相似文献
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Direct observation of global protein motion in hemoglobin and myoglobin on picosecond time scales 总被引：3，自引：0，他引：3
Picosecond phase-grating spectroscopy is highly sensitive to density changes and provides a new holographic approach to the study of protein dynamics. Photodissociation of carbon monoxide from heme proteins induces a well-defined transition from a ligated to a deoxy structure that is important to hemoglobin and myoglobin functionality. Grating spectroscopy was used to observe protein-driven density waves on a picosecond time scale after carbon monoxide dissociation. This result demonstrates that global tertiary structure changes of proteins occur on an extremely fast time scale and provides new insight into the biomechanics of deterministic protein motion. 相似文献
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Zheng J Kwak K Asbury J Chen X Piletic IR Fayer MD 《Science (New York, N.Y.)》2005,309(5739):1338-1343
In general, the formation and dissociation of solute-solvent complexes have been too rapid to measure without disturbing the thermal equilibrium. We were able to do so with the use of two-dimensional infrared vibrational echo spectroscopy, an ultrafast vibrational analog of two-dimensional nuclear magnetic resonance spectroscopy. The equilibrium dynamics of phenol complexation to benzene in a benzene-carbon tetrachloride solvent mixture were measured in real time by the appearance of off-diagonal peaks in the two-dimensional vibrational echo spectrum of the phenol hydroxyl stretch. The dissociation time constant tau(d) for the phenol-benzene complex was 8 picoseconds. Adding two electron-donating methyl groups to the benzene nearly tripled the value of tau(d) and stabilized the complex, whereas bromobenzene, with an electron-withdrawing bromo group, formed a slightly weaker complex with a slightly lower tau(d). The spectroscopic method holds promise for studying a wide variety of other fast chemical exchange processes. 相似文献
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The recent introduction of Fourier transform methods is revolutionizing IR and NMR spectroscopy. The application of IR interferometry or of NMR pulse methods, followed by Fourier transformation of the resultant interferogram, permits acquisition of spectral data in a time that is orders of magnitude less than by conventional spectroscopic methods. This reduction in time permits the study of transient species, or by "time-averaging" procedures S/N may be improved without the expenditure of inordinate amounts of time. The FT methods finds especially important application in the study of NMR spectra of nuclei of low sensitivity and low abundance, such as (13)C. 相似文献
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Broadfoot AL Herbert F Holberg JB Hunten DM Kumar S Sandel BR Shemansky DE Smith GR Yelle RV Strobel DF Moos HW Donahue TM Atreya SK Bertaux JL Blamont JE McConnell JC Dessler AJ Linick S Springer R 《Science (New York, N.Y.)》1986,233(4759):74-79
Data from solar and stellar occultations of Uranus indicate a temperature of about 750 kelvins in the upper levels of the atmosphere (composed mostly of atomic and molecular hydrogen) and define the distributions of methane and acetylene in the lower levels. The ultraviolet spectrum of the sunlit hemisphere is dominated by emissions from atomic and molecular hydrogen, which are kmown as electroglow emissions. The energy source for these emissions is unknown, but the spectrum implies excitation by low-energy electrons (modeled with a 3-electron-volt Maxwellian energy distribution). The major energy sink for the electrons is dissociation of molecular hydrogen, producing hydrogen atoms at a rate of 10(29) per second. Approximately half the atoms have energies higher than the escape energy. The high temperature of the atmosphere, the small size of Uranus, and the number density of hydrogen atoms in the thermosphere imply an extensive thermal hydrogen corona that reduces the orbital lifetime of ring particles and biases the size distribution toward larger particles. This corona is augmented by the nonthermal hydrogen atoms associated with the electroglow. An aurora near the magnetic pole in the dark hemisphere arises from excitation of molecular hydrogen at the level where its vertical column abundance is about 10(20) per square centimeter with input power comparable to that of the sunlit electroglow (approximately 2x10(11) watts). An initial estimate of the acetylene volume mixing ratio, as judged from measurements of the far ultraviolet albedo, is about 2 x 10(-7) at a vertical column abundance of molecular hydrogen of 10(23) per square centimeter (pressure, approximately 0.3 millibar). Carbon emissions from the Uranian atmosphere were also detected. 相似文献