Some Effects of Quantization of Internal Rotation on Spin-Lattice Relaxation and Hyperfine Structure

Abstract

The temperature dependence of the spin-lattice relaxation time of the oriented ${\mathrm{H}}_{3}$C-$\stackrel{\ifmmode \dot{}\else \.{}\fi{}}{\mathrm{C}}{R}_{1}{R}_{2}$ radical in x-irradiated single crystals of acetyl-($d, l$)-alanine has been observed to be dominated by "spin-flip" transitions between the rotational states of the methyl group. The energy separation of these levels has been confirmed by an analysis of the ESR spectra of the radical. The low-temperature ESR spectra show quantum effects also not previously observed.