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An investigation of molecular motion in stearic acid by proton magnetic resonance Cyr, Theodore J.R.


The proton magnetic resonance absorption of the C-form of stearic acid has been studied, over the temperature range 77°K to 3^2.5°K. The broadline spectra are decomposed into a wide and narrow component for solid and liquid regions in the lattice respectively. The appearance of the narrow component on the usual broadline spectrum at temperatures greater than room temperature is interpreted to be caused, by large liquid regions in the lattice. The number and size of these defects increase with increase in temperature and. with the incorporation of various types of defects in the solid lattice The spin-lattice relaxation times, T₁, were measured by adiabatic rapid, passage. The results indicate that the principal zeeman energy-thermal bath coupling occurs through methyl group reorientations. An activation energy of 2.2 kcalories/mole for methyl group rotation about the C₃ axis in solid stearic acid and a rotation frequency of 4 x 10⁵ sec⁻¹ at 77°K were determined from the T₁ data.

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