Dresden 2020 – wissenschaftliches Programm
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TT 46.19: Poster
Mittwoch, 18. März 2020, 15:00–19:00, P2/2OG
Temperature evolution of molecular-reorientation modes in CuPOF — •D. Opherden1,2, C. P. Landee3, F. Bärtl1,2, R. Stern4, I. Heinmaa4, J. Wosnitza1,2, and H. Kühne1 — 1Hochfeld-Magnetlabor Dresden (HLD-EMFL), HZDR, Dresden, Germany — 2Institut für Festkörper- und Materialphysik, TU Dresden, Germany — 3Department of Physics, Clark University, Worcester, Massachusetts, USA — 4Institute of Chemical Physics and Biophysics, Tallinn, Estonia
We present a detailed 31P-NMR spectroscopy and relaxometry study of molecular rotations in the metal-organic compound [Cu(pz)2(2-OHpy)2](PF6)2 (CuPOF). Here, a freezing of the PF6 rotation modes is revealed by a step-like increase of the temperature-dependent linewidth, accompanied by broad maxima of the longitudinal and transverse nuclear spin relaxation rates. An analysis based on the Bloembergen, Purcell, and Pound theory quantifies the related activation energies Ea/kB as 250 and 1400 K. The according characteristic correlation times of the local-field fluctuations, caused by the molecular rotation, are τ0 = 20 and 3 ps. Further, the second and fourth spectral moment of the 31P absorption line were calculated for a rigid lattice, as well as for different types of PF6 molecular-reorientation modes. The very good agreement between the experimental angular dependences of the second spectral moment and our numerical calculations clarifies the relevant symmetry axes of the PF6 rotation modes in the different temperature regimes.