OBSERVATION OF QUANTUM COHERENCE OF PARAMAGNETIC SPECIES BY MEANS OF SUDDEN MAGNETIC FIELD JUMP

本计画旨在利用光化学方法观察及深入研究瞬间形成自由基对的自旋相干现象。在自由基对存在的情况下，我们采用了两种不同的方法：1）外磁场的突然跳跃，2）在电子自旋共振条件下电磁场（微波场）的快速切换。自由基对使用激光脉冲照射几种溶液制备。我们采用的系统是a）聚亚甲基连接的双自由基，B）由光诱导电子转移反应形成的自由基-离子对，c）包括瞬时形成的自由基对的胶束系统。方法1）被应用于体系B），它显示了由磁场跳跃控制的反应，但我们意识到理论处理低磁场现象的困难。这项研究仍在调查中。方法2）对自由基对和自由基-离子对体系的自旋动力学提供了许多新的发现。首先，我们成功地观测到了几个自由基对系统的不同自旋量子拍频。拍频数据显示了微波场同时激发自由基对中的组分自由基所产生的双频信号。拍频信号的衰减被证明是由于自由基对中各向异性偶极-偶极相互作用引起的三重态-三重态失相现象。另一个重要的发现是在强微波场下出现了一个加宽的光谱图案，这也是由自旋退相效应合理化的。该项目表明，外场和/或电磁交变场的切换可以控制化学反应途径，并提供了许多有关光化学体系的自旋和化学动力学的重要信息。

This project aims at the observation and deep investigation of the spin coherent phenomenon of radical pairs formed transiently by photochemical method. We employed two different methods under the existence of radical pairs : 1) sudden jumping of the external magnetic field, 2) quick switching of the electromagnetic field (microwave field) under the conditions of the electron spin resonance. The radical pairs are prepared using a laser pulse irradiation to several solutions. The systems we employed were a) polymethylene-linked biradical, b) radical-ion pairs formed by photoinduced electron transfer reaction, c) micellar systems that include transiently formed radical pairs. Method 1) was applied to the the system b) and it showed the controlled reaction by the magnetic field jump, but we realized the difficulty of the theoretical handling of low magnetic field phenomenon. This study is still under investigation. Method 2) provided many new discoveries about the spin dynamics of radical pair and radical-ion pair systems. First of all, we succeeded in observing the different spin quantum beats of several radical pair systems. The beat data showed the double tequency signal due to simultaneous excitation of the component radicals of radical pairs by microwave field. The decay of the beat signal was proved to be due to the triplet-triplet dephasing phenomenon probably induced by anisotropic dipole-dipole interaction in the radical pair. Another important finding is the appearance of a broadened spectral pattern under the strong microwave field, that was also rationalized by the spin dephasing effect. This project apparently demonstrated that the switching of the external field and/or the electromagnetic alternating field can control the chemical reaction pathways and it also provides a lot of important information about the spin and chemical dynamics of photochemical systems.