Development of a new spectroscopy based on several transient lens effects and its application to chemical reactions

光化学反应中的反应体积变化和热变是表征反应的重要物理量。然而，由于缺乏足够高灵敏度和高时间分辨率的合适方法来检测这些量，阻碍了我们对许多化学反应的详细了解。在这项研究中，我们开发了高灵敏度和高时间分辨率的测量这些量的新技术，使用所谓的热透镜装置。我们发现了光激发后透镜信号的各种来源，如布居透镜、温度透镜、克尔透镜和体积透镜。利用这些组分，在恒温、恒压的溶剂中，成功地测量了化学反应和光物理过程的反应体积、热变、偏摩尔体积和热能。为此，我们提出了一种新的方法--瞬变透镜法。此外，我们还发现了有机分子在溶液中光激发后观察到的瞬时光栅信号的各种来源，如温度光栅、团簇光栅和体积光栅。利用光栅法研究了化学反应中出现的瞬时自由基的平移扩散过程。与大小和形状相似的非自由基分子相比，自由基的扩散常数很小。通过温度依赖关系和分子大小依赖关系对这一反常扩散过程进行了详细的研究。这项研究将揭示一个有趣的自由基-溶剂分子间相互作用领域。

Reaction volume changes and enthalpy changes in a photochemical reaction are very important quantities to characterize the reaction. However, a lack of suitable method for detecting these quantities with a sufficiently high sensitivity and high time resolution prohibits our detailed understanding of many chemical reactions. In this study, we have developed new techniques for measuring these quantities with high sensitivity and high time resolution using the so-called 'thermal lens' setup. We have discovered various origins of the lens signals after the photoexcitation, such as the population lens, temperature lens, Kerr lens, and volume lens. By using these components, the reaction volume, enthalpy change, partial molar volume and heat energy form chemical reactions and photophysical processes are successfully measured under a constant temperature, and a constant pressure in a solvent. Therefore we proposed a new name "transient lens method" for these techniques. Furthermore we have discovered various origins for the transient grating signals observed after photoexcitation of organic molecules in solutions, such as temperature grating, cluster grating, and volume grating. By using the grating technique, the translational diffusion process of transient radicals appeared in chemical reactions is investigated. The diffusion constants of the radicals are found to be very small compared with the non-radical molecules with similar sizes and shapes. This anomalous diffusion process is studied in detail by the temperature dependence and molecular size dependence. This study will reveal an interesting field of radicalsolvent intermolecular interaction.