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681.
以量子化学计算作为起点, 为最简单的糖类分子——乙醇醛开发了两套分子力学力场参数: 基于肽类的力场和基于醛类的力场. 分子动力学模拟结果表明, 所开发的类醛力场参数能够较好地描述乙醇醛分子在水中的结构以及水分子在其周围的分布. 通过瞬时简正模式分析, 得到了3N-6个模式的瞬时振动频率和振动跃迁偶极矩等振动光谱参数的统计分布及其相关性. 结合量子化学计算和分子动力学模拟对生物分子体系的多元振动光谱参数进行预测和评估, 为从化学键水平出发模拟宽带飞秒二维红外相关光谱提供了一个新方法. 相似文献
682.
AUMILER Damir 《中国科学B辑(英文版)》2009,52(8):1148-1153
The intersystem crossing and isomerization dynamics of free-Cy3, Cy3-ssDNA, free-Cy5 and Cy5-ssDNA are obtained through simple
analysis of rapid on/off blinking from single molecule fluorescence intensity time-traces and the fluorescence correlation
spectroscopy (FCS). The on- and off-times observed in fluorescence time traces of single cyanine dyes are due to the formation
of the triplet state and isomerization, where both the interaction with DNA and long central polymethine chain of cyanine
dyes increase the barriers of isomerization, leading to long off-time. The results indicate that the single molecule fluorescence
fluctuation together with the resulting second autocorrelation analysis are powerful methods for determining the triplet state
and isomerization dynamics, which could be the simple techniques and complementary to other spectroscopic techniques, such
as fluorescence decay measurement and laser flash photolysis to study the photophysical processes of complex molecules.
Supported by the National Natural Science Foundation of China (Grant Nos. 20773139, 20833008 & 20825314), and State Key Project
for Fundamental Research (Grant Nos. 2006CB806000 & 2007CB815200) 相似文献
683.
Yulu Li Dr. Xiao Luo Dr. Tao Ding Prof. Dr. Xin Lu Prof. Dr. Kaifeng Wu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(34):14398-14401
Lead halide perovskite nanocrystals (NCs) hold strong promise for a variety of light-harvesting, emitting, and detecting applications, all of which, however, could be complicated by multicarrier Auger recombination. Therefore, complete documentation of the size- and composition-dependent Auger recombination rates of these NCs is highly desirable, as it can guide system design in many applications. Herein we report the synthesis and Auger measurements of monodisperse APbX3 (A=Cs and FA; X=Cl, Br, and I) NCs in an extensive size range (ca. 3–9 nm). The biexciton Auger lifetime of all the NCs scales linearly with the NC volume. The scaling coefficient is virtually independent of the cation but rather depends sensitively on the anion, and is 0.035, 0.085, and 0.142 ps nm−3 for Cl, Br, and I, respectively. In all of these nanocrystals the Auger recombination is much faster than in standard CdSe and PbSe NCs (ca. 1 ps nm−3). 相似文献
684.
Guang‐Yue Li Guang‐Jiu Zhao Ke‐Li Han Guo‐Zhong He 《Journal of computational chemistry》2011,32(4):668-674
Proton transfer (PT) and excited‐state PT process are proposed to account for the fluorescent sensing mechanism of a cyanide chemosensor, 8‐formyl‐7‐hydroxycoumarin. The time‐dependent density functional theory method has been applied to investigate the ground and the first singlet excited electronic states of this chemosensor as well as its nucleophilic addition product with cyanide, with a view to monitoring their geometries and spectrophotometrical properties. The present theoretical study indicates that phenol proton of the chemosensor transfers to the formyl group along the intramolecular hydrogen bond in the first singlet excited state. Correspondingly, the nucleophilic addition product undergoes a PT process in the ground state, and shows a similar structure in the first singlet excited state. This could explain the observed strong fluorescence upon the addition of the cyanide anion in the relevant fluorescent sensing mechanism. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2011 相似文献
685.
实验构型分析是定量分析和频振动光谱的基础.变换实验构型,不仅要考虑某一振动模式信号强度的大小,还要考虑不同构型下的信号检测效率.现有的和频振动光谱实验构型分析主要考虑前者.本文探讨实验构型分析中所涉及的信号检测效率问题,模拟在共向式和频(差频)及对射式和频(差频)振动光谱实验中选取何种实验构型对采集信号光更加合理有效.利用相干光学过程能量守恒和动量守恒原理,分析了入射角及入射光频率等因素对信号出射角的影响,并模拟了信号出射角与入射角及入射光频率的关系,得到了可选的入射角组合最多、出射角随入射光频率变化最小的实验构型.结果表明,和频振动光谱采取共向式实验构型,差频振动光谱采取对射式实验构型,有利于信号采集,进而有利于用实验构型分析方法对和频(差频)振动光谱进行定量研究. 相似文献
686.
687.
Jing‐Heng Meng Xiao‐Jiao Deng Zi‐Yu Li Prof. Dr. Sheng‐Gui He Prof. Dr. Wei‐Jun Zheng 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(19):5580-5583
The first example of a metal oxide cluster anion, La6O10? that can activate methane under ambient conditions is reported. This reaction is facilitated by the oxygen‐centered radical (O??) and follows the hydrogen atom transfer mechanism. The La6O10? has a high vertical electron detachment energy (VDE=4.06 eV) and a high symmetry (C4v). 相似文献
688.
We have developed a compact photoelectron imaging facility, including an anion source with dissociative photoelectron attachment to molecules, a linear time-of-flight mass spec-trometry (TOFMS), and an orthogonal high-resolution threshold photoelectron velocity map imaging spectrometer (VMI). Intense and cold cluster anions were prepared in photoelectron- attachment processes upon pulsed UV laser ablation of metal target. Combining this anion source with TOFMS-VMI, the achieved mass resolution is about 200, and the electron ki- netic energy resolution is better than 3%, i.e., 30 meV for 1 eV electrons. More importantly, low-energy photoelectron imaging spectra for CH3S- and S2- at 611.46 nm are obtained. In both cases, the refined electron affinities are determined to be 1.86264-0.0020 eV for CH3S and 1.67444-0.0035 eV for S2, respectively. Preliminary results suggest that the apparatus is a powerful tool for estimating precise electron affinities values from threshold photoelectron imaging spectroscopy. 相似文献
689.
《Comptes Rendus de l''Academie des Sciences Series IIB Mechanics Physics Astronomy》2001,4(11):805-808
We present a time evolution of 1H spin-lattice relaxation rates in the laboratory (1/T1) and in the rotating (1/T1ρ) frame of a synthetic cement paste. The typical results found for both rates allow us to follow the main hydration stages of the cement paste and the refinement of its microporosity. In particular the texturation of the porosity and the structuration of the surface of the material are evidenced on two model cement pastes. An interpretation in terms of fractal size distribution is considered as well as the effect of the curing temperature. 相似文献
690.
采用266nm紫外激光对间氟溴苯和对氟溴苯进行了光解动力学研究,在多个角度探测了光解碎片Br和C6H4F的时间飞渡谱(TOF)。从光解碎片的平动能分布P(Et)可以得到:间氟溴苯和对氟溴苯大约有46.8%和41.7%的可资用能分配到碎片的平动能,其余的分配到碎片的内能;且各向异性参数被确定为0.7和-0.4。为了更好地解释实验结果,我们利用从头计算方法对反应体系进行了计算,并与实验结果吻合,由此,我们提出了比较合理的光解机理且对氟原子的取代效应进行了讨论。 相似文献