Reaction Dynamics in Solution Studied by Ultrafast Visible Pump - Far Infrared Probe Technique

我们开发了两种新的光源和红外光谱技术来研究凝聚相中的化学反应和弛豫现象。一种是利用强飞秒红外脉冲的红外三阶非线性光学光谱学。红外脉冲是由差频、光学参量产生/放大等光学非线性过程产生的。通过在光路中插入硅板来补偿脉冲中的群速度色散。用自相关方法测得脉冲宽度为55ps，能量大于微焦耳/脉冲，是目前已知的能量如此高的红外脉冲中最短的脉冲。利用该脉冲，我们构建了非线性光谱学的光学系统，如瞬变光栅、包括频率分辨形式的2脉冲和3脉冲光子回波。频率分辨三脉冲光子回波是…的一种更多的是二维振动光谱。我们已经将这些技术应用于极性溶剂中的三原子离子(OCN^-和SCN^-)、有机大分子的-N=C=N-反伸缩模式、金属卟啉的C=O伸缩模式和氰铁络合物的CN伸缩模式等几种振动模式。我们讨论了这些模的振动动力学，包括振动布居驰豫、纯振动退相、动力学涨落和谱扩散、跃迁频率的不均匀性等。我们开发的另一种技术是使用太赫兹(THz)辐射的光谱方法。太赫兹辐射是通过将飞秒脉冲聚焦到半导体晶片上而产生的，并通过向晶片施加磁场来放大。太赫兹辐射是通过电光采样方法进行检测的。利用太赫兹辐射为光源的远红外光谱仪，测量了大块液体、电荷转移络合物溶液、生物聚合物等各种凝聚相体系的远红外吸收光谱。特别是对多肽和蛋白质(细胞色素c)的远红外光谱进行了详细的研究，讨论了生物聚合物的结构与低频区光谱的关系。较少

We have developed two new light sources and spectroscopic techniques in the infrared region to investigate the chemical reactions and relaxation phenomena in condensed phases under this project. One is the third order optical nonlinear spectroscopy in the infrared region using intense femtosecond infrared pulses. The infrared pulses are generated by some optical nonlinear processes such as difference frequency mixing and optical parametric generation/amplification. Group velocity dispersion in the pulse is compensated by inserting a silicon plate in the optical path. The pulse width is measured to be 55 fs with an energy of more than microJ/pulse by an autocorrelation method, which is the shortest pulse of the infrared pulse with such a high energy to our knowledge. Using this pulse we have constructed optical systems of nonlinear spectroscopy such as transient grating, 2- and 3-pulse photon echo including frequency-resolved version. The frequency-resolved 3-pulse photon echo is one of … More the two-dimensional vibrational spectroscopies. We have applied these techniques to several vibrational modes such as three-atom ions (OCN^- and SCN^-) in polar solvents, the -N=C=N- antistretching modes of large organic molecules, the C=O stretching modes of metal porphyrines, and the CN stretching modes of cyano-iron complexes. We discuss vibrational dynamics of these modes including vibrational population relaxation, pure vibrational dephasing, dynamical fluctuation and spectral diffusion, inhomogeneity of the transition frequency, and so on. The other technique we have developed is a spectroscopic method using terahertz (THz) radiation. The THz radiation is generated by focusing a femtosecond pulse to a semiconductor wafer and amplified by applying a magnetic field to the wafer. The THz radiation is detected by an electro-optic sampling method. By using spectrometer in the far-infrared region with the THz radiation as a light source, we have measured far-infrared absorption spectra of various kinds of condensed phase systems such as bulk liquids, solutions of charge-transfer complexes, biopolymers, and so on. Especially, far infrared spectra of polypeptides and proteins (cytochrom c) were studied in detail, and we discuss relation between structures of the biopolymers and spectra in the low-frequency region. Less