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第十五届全国化学动力学会议

作者：张峰 Hong-Wei Wang Keisuke Tominaga michitoshi hayashi Molecular Photoscience Research Center Kobe University Center for Condensed Matter Science Taiwan University

Thanks to the significant advance of terahertz（THz） technology in the past two decades, THz spectroscopy has become a routine characteristic tool in many laboratories. To the chemistry science, the most significant of THz spectroscopy is that it gives a direct access to non-covalent interactions. We have been dedicated to resolve the fundamental problem—mode assignment—of THz spectroscopy as applied to a broad spectrum of non-covalent systems. These systems involve fullerene, aromatic hydrocarbons, carbohydrates, pharmaceuticals, nucleobases, nucleosides, amino acids, short-chain peptides and polymers. We have made progresses in primarily two respects. First, we have achieved accurate solid-state ab initial simulations of THz bands as shown in Fig. 1 by taking a few examples for illustration. Second, we developed an independent mode analysis method to evaluate the percentage contributions of external translations, librations, and a set of internal modes with unambiguous physical meaning to any THz mode of interest;so that we have achieved THz mode assignment at the quantitative level.[1, 2] On this theoretical basis, we have illustrated several promising advantages of THz spectroscopy in crystallography, especially when hydrogen atoms, which are invisible to X-ray, play important roles in the determination of crystal structures. In particular, we examined the symmetry-conservation principle of polymer science[3] and studied elementary structural units of a disordered molecular system with using THz spectroscopy.

关键词： terahertz spectroscopy solid-state density functional theory mode analysis

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Density matrix method and ultrafast processes

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Science China Chemistry 2012年第4期55卷 579-593页

作者： NIU YingLi LIN ChihKai ZHU ChaoYuan MINEO Hirobumi CHAO ShengDer FUJIMURA Yuichi hayashi michitoshi LIN ShengHsien Key Laboratory of Organic Solids Beijing National Laboratory for Molecular Science(BNLMS)Institute of ChemistryChinese Academy of SciencesBeijing 100190China Institute of Modern Physics Northwest UniversityXi’an 710069China Department ofChemistry Faculty ofScienceTohoku UniversitySendai 980Japan

When femto-second (fs) time-resolved experiments are used to study ultrafast processes, quantum beat phenomena are often observed. In this paper, to analyze the fs time-resolved spectra, we will present the density matrix method, a powerful theoretical technique, which describes the dynamics of population and coherence of the system. How to employ it to study the pump-probe experiments and fs ultrafast processes is described. The ππ*→nπ* transition of pyrazine is used as an example to demonstrate the application of the density matrix method. Recently, Suzuki's group have employed the 22 fs time resolution laser to study the dynamics of the ππ* state of pyrazine. In this case, conical intersection is commonly believed to play an important role in this non-adiabatic process. How to treat the effect of conical intersection on non-adiabatic processes and fs time-resolved spectra is presented. Another important ultrafast process, vibrational relaxation, which takes place in sub-ps and ps range and has never been carefully studied, is treated in this paper. The vibrational relaxation in water dimer is chosen to demonstrate the calculation. It should be noted that the vibrational relaxation of (H2O)2 has not been experimentally studied but it can be accomplished by the pump-probe experiments.

关键词：密度矩阵方法超快过程飞秒时间分辨光谱振动弛豫绝热过程实验拍现象连贯性

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