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Zeitschrift für Physikalische Chemie

International journal of research in physical chemistry and chemical physics

Ed. by Rademann, Klaus

12 Issues per year


IMPACT FACTOR 2015: 1.183

SCImago Journal Rank (SJR) 2015: 0.491
Source Normalized Impact per Paper (SNIP) 2015: 0.520
Impact per Publication (IPP) 2015: 1.133

Online
ISSN
2196-7156
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Deuteron Magnetic Resonance Studies of Anhydrous Caffeine

Andre Nowaczyk
  • Technische Universität Dortmund, Fakultät für Physik, Dortmund, Deutschland
/ Ramesh Chandra Nath
  • Technische Universität Dortmund, Fakultät für Physik, Dortmund, Deutschland
/ Herbert Zimmermann
  • Max Planck Institut für Medizinische Forschung, Heidelberg, Deutschland
/ Roland Böhmer
Published Online: 2012-10-29 | DOI: https://doi.org/10.1524/zpch.2012.0333

Abstract

Methyl deuterated caffeine powder was studied using 2H-NMR relaxometry and line shape analysis. In caffeine's low-temperature phase the spin-lattice relaxation times indicate a thermally activated CD3 reorientation (activation energy ≈4 kJ/mol). Below the T1 minimum near 35 K the quadrupolar echo spectra develop features indicative for quantum mechanical tunneling. Dielectric measurements indicate the presence of dipole moment fluctuations with times scales that follow an Arrhenius law (energy barrier ≈107 kJ/mol). It is argued that the underlying motion involves small-angle molecular excursions and therefore remains undetected via stimulated-echo spectroscopy. The hysteresis accompanying the order/disorder transition taking place above 400 K was monitored using solid-echo line shapes as well as via spin relaxation times. In the high-temperature phase indications for the onset of anisotropic large-angle motions were obtained.

Keywords: Phase Transitions; Spin-Lattice Relaxation; Echo Spectroscopy

About the article

* Correspondence address: Technische Universität Dortmund, Fakultät für Physik, 44221 Dortmund, Deutschland,


Published Online: 2012-10-29

Published in Print: 2012-12-01


Citation Information: Zeitschrift für Physikalische Chemie, ISSN (Online) 2196-7156, ISSN (Print) 0942-9352, DOI: https://doi.org/10.1524/zpch.2012.0333. Export Citation

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