Magnetic field effect on a radical pair reaction as a probe of microviscosity.
Magnetic field effect on a radical pair reaction as a probe of microviscosity.
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磁场对自由基对反应的影响作为微观粘度的探针。
DOI：
10.1021/jp804862w
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发表时间：
2008
期刊：
影响因子：
--
通讯作者：
M. Wakasa
中科院分区：
文献类型：
--
作者：
A. Hamasaki;T. Yago;M. Wakasa
用纳秒激光闪光光解技术研究了在不同粘度(ETA=0.55~59.2CP)的乙醇溶液中，二苯甲酮与硫酚的光诱导吸氢反应中Delta g机理引起的磁场效应.在1.6T下观察到的相对产率R(1.6T)=Y(1.6T)/Y(0T)，在0.55Cp<；或=Eta<；或=5Cp的范围内，随着ETA的增加而降低，在5Cp<；Eta<；或=55.3Cp的范围内，随着ETA的增加而增加。当ETA大于55.3Cp时，R(1.6T)值变为1.0，MFE完全猝灭。在考虑了硫等重原子的自旋-轨道耦合效应的情况下，用随机Liouville方程(SLE)分析了观测到的MFE的ETA依赖性。SLE分析很好地再现了观察到的MFE。SLE得到的自由基扩散系数比宏观溶剂粘度估计的扩散系数小约三倍。人们可以通过观察现有光化学反应体系上的MFE来探测自由基对附近的微观粘度。
The magnetic field effects (MFEs), caused by the Delta g mechanism, on the photoinduced hydrogen abstraction reaction of benzopheneone with thiophenol were investigated in alcoholic solutions of varying viscosities (eta = 0.55 to 59.2 cP) by a nanosecond laser flash photolysis technique. The escape yield of benzophenone ketyl radicals ( Y) gradually decreased with increasing magnetic field strength ( B) from 0 to 1.6 T. The relative yield observed at 1.6 T, R(1.6 T) = Y(1.6 T)/ Y(0 T), decreased with increasing eta in the range of 0.55 cP < or = eta < or = 5 cP, and then increased with increasing eta in the range of 5 cP < eta < or = 55.3 cP. When eta was higher than 55.3 cP, the R(1.6 T) value became 1.0, and MFEs were completely quenched. The observed eta dependence of the MFEs was analyzed by the stochastic Liouville equation (SLE), in which the effects of spin-orbit coupling by a heavy atom such as sulfur were taken into account. The observed MFEs were reproduced fairly well by the SLE analysis. The diffusion coefficients of the radicals obtained by the SLE were about three times smaller than those expected from the macroscopic solvent viscosities. One can probe the microviscosity in the vicinity of the radical pairs by observing MFEs on the present photochemical reaction system.