Department of Physics, Bryn Mawr College, 101 North Merion Avenue, Bryn Mawr, Pennsylvania 19010-2899, USA.
J Chem Phys. 2012 Feb 7;136(5):054508. doi: 10.1063/1.3677183.
We report (1)H spin-lattice relaxation measurements in polycrystalline 4,4'-dimethoxybiphenyl at temperatures between 80 and 300 K at NMR frequencies of ω(0)/2π = 8.50, 22.5, and 53.0 MHz. The data are interpreted in terms of the simplest possible Bloch-Wangsness-Redfield methyl group hopping model. Different solid states are observed at low temperatures. The (1)H spin-lattice relaxation is nonexponential at higher temperatures where a stretched-exponential function fits the data very well, but this approach is phenomenological and not amenable to theoretical interpretation. (We provide a brief literature review of the stretched-exponential function.) The Bloch-Wangsness-Redfield model applies only to the relaxation rate that characterizes the initial (1)H magnetization decay in a high-temperature nonexponential (1)H spin-lattice relaxation measurement. A detailed procedure for determining this initial relaxation rate is described since large systematic errors can result if this is not done carefully.
我们报告了（1）H 核自旋晶格弛豫测量在多晶 4,4'-二甲氧基联苯在温度 80 至 300 K 之间在 NMR 频率ω（0）/2π = 8.50、22.5 和 53.0 MHz。数据根据最简单的 Bloch-Wangsness-Redfield 甲基基团跳跃模型进行解释。在低温下观察到不同的固态。在较高温度下，（1）H 自旋晶格弛豫是非指数的，其中拉伸指数函数非常好地拟合数据，但这种方法是唯象的，不适于理论解释。（我们提供了拉伸指数函数的简要文献综述。）Bloch-Wangsness-Redfield 模型仅适用于在高温非指数（1）H 自旋晶格弛豫测量中表征初始（1）H 磁化强度衰减的弛豫率。由于如果不仔细进行操作，可能会导致较大的系统误差，因此描述了确定此初始弛豫率的详细过程。
