Structure and lattice dynamics of dipolarly disordered 2,3-dimethylanthracene crystals

Authors

M. Dörr, Experimentalphysik I, Universität Bayreuth, D-95440 Bayreuth, Germany
H. Gerlach, Organische Chemie II, Universität Bayreuth, D-95440 Bayreuth, Germany
J. Kalus, Experimentalphysik I, Universität Bayreuth, D-95440 Bayreuth, Germany
N. Karl, Physikalisches Institut, 3 Universität Stuttgart, Pfaffenwaldring 57, D-70569 Stuttgart, Germany
M. Monkenbusch, Forschungszentrum Jüulich GmbH, Institut für Festkörperforschung, D-52425 Jülich, Germany
I. Natkaniec, Joint Institute for Nuclear Research, PO Box 79, Dubna, 101000 Moscow, Russian Federation
U. Schmelzer, Experimentalphysik I, Universität Bayreuth, D-95440 Bayreuth, Germany
W. Schmidt, Institut Laue–Langevin, F-38042 Grenoble Cédex 9, France
John J. Stezowski, University of Nebraska - LincolnFollow
P. Vorderwisch, Hahn–Meitner-Institut Berlin, Berlin Neutron Scattering Centre, D-14109 Berlin, Germany
M. Warth, Physikalisches Institut, 3 Universität Stuttgart, Pfaffenwaldring 57, D-70569 Stuttgart, Germany

Date of this Version

July 1998

Comments

Published in Journal of Physics: Condensed Matter 10 (1998), pp. 10879–10899. PII: S0953-8984(98)96015-5. Copyright © 1998 IOP Publishing Ltd. Used by permission. http://www.iop.org/EJ/journal/JPhysCM

Abstract

2,3-dimethylanthracene (2,3-DMA, C₁₆H₁₄) crystallizes in a pseudocentrosymmetric triclinic lattice with two molecules per unit cell showing dipolar structural disorder of the acentric molecules. Using powder samples the amplitude weighted phonon density of states was measured by inelastic incoherent neutron scattering for different degrees of deuteration. The differences in the resulting spectra can be explained by changes of the dynamics of the molecular bodies or the methyl side groups. By the method of inelastic coherent neutron scattering phonon dispersion curves were determined. The phonon lines are broad even at low temperatures; this fact is supposed to be related to dipolar disorder. Both the incoherent and coherent scattering results can be described satisfactorily by lattice dynamical calculations using a “6-exp” potential for the atom–atom interactions of different molecules, including internal degrees of freedom.