Abstract
Abstract The EPR hyperfine coupling constants, linewidths, and rotational correlation times have been measured for di-tert-butyl nitroxide (DTBN) doped in adamantane. At low paramagnetic impurity concentrations, the nitrogen hyperfine coupling constant decreases from aN = 16.7 ± 0.2 G to 15.8 ± 0.2 G, the linewidth increases from 0.57 ± 0.05 G to 1.0 ± 0.05 G, and the rotational correlation time decreases from 1.5 × 10−10 sec to 1.5 × 10−11 sec as the temperature is decreased from -20°C to -65°C. A plastic crystal to brittle crystal phase transformation occurs at -65°C. The hyperfine coupling constant remains constant, the linewidth goes through a maximum and decreases, and the rotational correlation time goes through a minimum and increases as the temperature is lowered through the phase transition. Rapid motion persists even at -130°C. No unequivocal evidence for anisotropic reorientation was found but the unusually large values of aN may be attributed to an ehanced tumbling about the long axis of the m...
Published Version
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