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o-Terphenyl: flips of the end rings in the crystal phase

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Stumber,  Michael
Research Group Prof. Dr. Haeberlen, Max Planck Institute for Medical Research, Max Planck Society;

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Zimmermann,  Herbert
Department of Molecular Physics, Max Planck Institute for Medical Research, Max Planck Society;
Department of Biomolecular Mechanisms, Max Planck Institute for Medical Research, Max Planck Society;

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Schmitt,  Heike
Department of Molecular Neurobiology, Max Planck Institute for Medical Research, Max Planck Society;

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Haeberlen,  Ulrich
Research Group Prof. Dr. Haeberlen, Max Planck Institute for Medical Research, Max Planck Society;

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Citation

Stumber, M., Zimmermann, H., Schmitt, H., & Haeberlen, U. (2001). o-Terphenyl: flips of the end rings in the crystal phase. Molecular Physics, 99(13), 1091-1098. doi:10.1080/00268970110042613.


Cite as: https://hdl.handle.net/11858/00-001M-0000-0029-232B-7
Abstract
We demonstrate by selective saturation deuteron NMR experiments on a crystal of selectively deuterated o-terphenyl (OTP) that both end rings I and II attached to the central ring undergo thermally activated flip motions. In crystals of OTP, the end rings I and II are not symmetry related, their dynamics can be different and, in fact, is different, although mutual steric hindrance of the rings suggests a strong correlation. We measured the rates k I and k II of the flips of both end rings I and II as a function of temperature. We find that, independent of the temperature, k I exceeds k II by roughly a factor of 100. This result excludes correlated flips of rings I and II in the sense that a flip of one ring necessarily entails a flip of the other. The activation energies EaI and EaII of the two flip processes turn out to be equal (80.5 kJ mol−1) within experimental errors. This is taken as a hint that the flips are, after all, related to each other. A mechanism is proposed of how this is possible under the constraint k I » k II.