Methyl Group Rotation, H-1 Spin-Lattice Relaxation in an Organic Solid, and the Analysis of Nonexponential Relaxation

Authors

Peter A. Beckmann, Bryn Mawr CollegeFollow
Evan Schneider

Document Type

Article

Version

Publisher's PDF

Publication Title

Journal of Chemical Physics

Volume

136

Publication Date

2012

Abstract

We report ¹H spin-lattice relaxation measurements in polycrystalline 4,4^′-dimethoxybiphenyl at temperatures between 80 and 300 K at NMR frequencies of ω₀/2π = 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 ¹H 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 ¹H magnetization decay in a high-temperature nonexponential ¹H 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.

Publisher's Statement

Copyright (2012) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in J. Chem. Phys. 136, 054508 (2012) and may be found at http://jcp.aip.org/resource/1/jcpsa6/v136/i5/p054508_s1.

Citation

P. A. Beckmann and E. Schneider, J. Chem. Phys. 136, 054508 (2012).

DOI

10.1063/1.3677183