The investigation of spin dynamics of radical pairs by the reaction yield detected magnetic resonance

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In this project, we intend to elucidate the reaction dynamics of radical pairs in sub-ps time range by the detectors with low time resolution, such as refractive index, optical rotation, etc., which is enabled by the reaction yield detected magnetic resonance (RYDMR) using a short microwave pulse. Since the linearity between the signal intensity and the microwave etfect on the product yield is evaluated to be reliable, we tried the simultaneous measurements of the transient optical absorption, i.e. a direct measurement, and that of product yield. After the stabilization of the sample flow, we measured the RYDMR spectrum and the reaction dynamics in X-band (9GHZ) region. In both measurements, the correspondence between these methods was very good. Furthermore, the indirect measurement can be done with lower microwave intensity and without the monitoring light for the optical absorption, which could aftord a better result. These apparatus were easily applied to the newly developed Ku-band (18GHz) RYDMR system because the detection systems are independent of the magnetic and the microwave fields. The measurement by the refractive index was not successful because the S/N ratio and the baseline stability were not good. On the other hand, the S/N ratio with the optical rotation detection was also low but, in some case, the observed rotation was a little larger than the initial solution. This seems that the radical pair recombination may compete with the inversion of radicals.