MOLECULAR ASPECTS OF DYNAMICS IN REACTION PROCESSES AND MOLECULAR INTERACTIONS IN SOLUTION

我们的研究项目的重点是光物理和光化学过程在溶液和玻璃中的超快光谱研究。为了阐明化学和生物过程中溶质-溶剂相互作用的动力学，研究了包括溶剂化、能量弛豫、电子/质子转移和光解产物之间的双相复合在内的物理化学过程。研制了空腔倾倒克尔透镜锁模Ti：蓝宝石激光器（12 fs）和Cr: forsterite激光器（26 fs），用于测量泵浦探针、三脉冲光子回波、克尔门发射、光学克尔光谱和荧光上转换光谱。我们对TPM染料进行了超快泵浦探针测量，时间分辨率为30秒。信号呈多指数衰减，慢速组分对溶剂粘度的线性依赖性较强。活化能和有效体积随衰变速度的减慢而增大。这一结果可以用随时间变化的粘度或溶剂化壳层结构的影响来解释。利用蓝铜蛋白，利用超快泵浦探针光谱研究了与光激发和电荷转移态无辐射失活相关的蛋白质动力学。观察到一个与其他局域拉曼模式相移的相干低频振动模式。这种低频率模式很可能归因于包括蛋白质骨架运动在内的离域模式。我们采用参考相互作用现场模型理论来估计溶质-溶剂体系平均能量的弛豫动力学以及从溶质分子的角度看溶剂的随时间径向分布函数。理论结果表明，与第一壳层相比，第二壳层的重排速度要慢一个数量级。我们认为，进一步的溶剂壳层的较慢弛豫在非均匀光谱宽度的动态弛豫中起着重要作用，这在我们之前的时间分辨空穴燃烧和荧光光谱实验中已经观察到。为了阐明偶极自由基在非极性和极性溶剂中的动力学行为，对溶液中双极自由基对的简单模型系统进行了分子动力学模拟。偶极-偶极相互作用稳定了自由基对，分离很小。偶极子对可以是实验观察到的夹心自由基二聚体的前体。偶极子对的构象可能不利于自由基的重组，这可能是对氨基苯基基自由基逃逸概率高的原因。我们演示了二维三脉冲光子回波测量染料掺杂PMMA在30K。当种群周期T延长到100 ~ 100 ps时，重相位和回波形成仍然明显，说明回波信号本身具有振动结构。少

The focus of our research project is the ultrafast spectroscopic study of photophysical and photochemical processes in solution and glasses. To elucidate the dynamics of the solute-solvent interactions in chemical and biological processes by the femtosecond laser spectroscopy, physico-chemical processes including solvation, energy relaxation, electron/proton transfer, and geminate recombination between photodissociation products are under investigation.Cavity-dumped Kerr-lens mode-locked Ti : sapphire laser(12 fs) and Cr : forsterite laser(26 fs) were developed for the measurements of pump-probe, three-pulse photon echo, Kerr-gate emission, optical Kerr, and fluorescence up-conversion spectroscopy.We have carried out ultrafast pump-probe measurements of TPM dyes with a time resolution of 30 fs. The signal decays in a multiexponential manner, and the slower components showed stronger linear dependence on the solvent viscosity than the faster ones. The activation energies and effective v … More olumes were larger for slower decays. The results can be explained by the effect of the time dependent viscosity or the hierarchy structure of the solvation shell.Using a blue copper protein, we have studied protein dynamics associated with optical excitation and radiationless deactivation of the charge transfer state by an ultrafast pump-probe spectroscopy. A coherent low frequency vibrational mode of which the phase shifted from those of the other localized Raman modes was observed. This low frequency mode most probably can be attributed to the delocalized mode including the protein skeletal motion.We employ a reference interaction-site model theory to estimate the relaxation dynamics of the average energy of solute-solvent systems as well as the time-dependent radial distribution functions of solvents viewed from the solute molecule. The theoretical results indicate that the rearrangement of the second solvent shell is about an order of magnitude slower compared with that of the first shell. We suggest that the slower relaxation of further solvent shells can play a significant role in the dynamic relaxation of the inhomogeneous spectral width, which has been observed in our previous experiment of the time resolved hole-burning and fluorescence spectroscopy.Molecular dynamics simulation of a simple model system of the geminate radical pair in solution has been performed to elucidate the dynamic behavior of the dipole radicals in nonpolar and polar solvents. The dipole-dipole interaction stabilized the radical pair with a small separation. The dipole pair can be the precursor of the experimentally observed sandwich radical dimer. The conformation of the dipole pair may not be favorable for the recombination of the radicals, which can be the reason of the high escape probability observed for the p-aminophenylthiyl radical.We have demonstrated two-dimensional three-pulse photon echo measurement of a dye doped PMMA at 30K. Rephasing and echo formation were still clear even when the population period, T, was extended to > 100 ps. The results indicate that the echo signal itself has the vibrational structure. Less