Electron spin relaxation of triarylmethyl radicals in fluid solution
Electron spin relaxation of triarylmethyl radicals in fluid solution
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DOI：
10.1006/jmre.2001.2379
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发表时间：
2001-09-01
影响因子：
2.2
通讯作者：
Halpern, HJ
中科院分区：
文献类型：
--
作者：
Yong, L;Harbridge, J;Halpern, HJ
本文用脉冲EPR方法测量了一种三芳基甲基自由基（对称三苯甲基）在水、1：1水：甘油和1：9水：甘油中L带、S带和X带的电子自旋弛豫时间。在水溶液中，T-1是17 +/- 1 μ s在X波段在环境温度下，几乎是独立的微波频率，并表现出很小的粘度依赖性。T-1在1：1水：甘油中的温度依赖性在20 ~ 80 K之间以拉曼过程为主。在较高的温度下，包括室温下，增加的自旋-晶格弛豫速率归因于调制自旋-轨道耦合的局部振动模式。在H2O溶液中，T-2在X波段为11 +/- 1 μ s，在L波段增加到13 +/- 1 μ s。对于更粘稠的溶剂混合物，T-2是比T-1短得多，弱的频率依赖性，这表明不完全的运动平均的超精细各向异性作出显着贡献的T-2。在水中，1：1水：甘油溶液连续波EPR线宽不是弛豫确定的，而是在较高粘度的1：9水：甘油溶液中变为弛豫确定的。250 MHz线宽的洛伦兹分量作为粘度的函数是在良好的协议与T-2确定的贡献，在较高的频率的线宽。(C)北京：科学出版社.
Electron spin relaxation times of a Nycomed triarylmethyl radical (sym-trityl) in water, 1 : 1 water: glycerol, and 1 : 9 water: glycerol were measured at L-band, S-band, and X-band by pulsed EPR methods. In H2O solution, T-1 is 17 +/- 1 mus at X-band at ambient temperature, is nearly independent of microwave frequency, and exhibits little dependence on viscosity. The temperature dependence of T-1 in 1 : 1 water: glycerol is characteristic of domination by a Raman process between 20 and 80 K. The increased spin-lattice relaxation rates at higher temperatures, including room temperature, are attributed to a local vibrational mode that modulates spin-orbit coupling. In H2O solution, T-2 is 11 +/- 1 mus at X-band, increasing to 13 +/- 1 mus at L-band. For more viscous solvent mixtures, T-2 is much shorter than T-1 and weakly frequency dependent, which indicates that incomplete motional averaging of hyperfine anisotropy makes a significant contribution to T-2. In water and 1 : 1 water: glycerol solutions continuous wave EPR linewidths are not relaxation determined, but become relaxation determined in the higher viscosity 1 : 9 water: glycerol solutions. The Lorentzian component of the 250-MHz linewidths as a function of viscosity is in good agreement with T-2-determined contributions to the linewidths at higher frequencies. (C) 2001 Academic Press.