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Incoherent neutron scattering in acetanilide and three deuterated derivatives

1991; American Physical Society; Volume: 43; Issue: 7 Linguagem: Inglês

10.1103/physrevb.43.5223

1095-3795

Mariette Barthès, Robert Almairac, Jean‐Louis Sauvajol, J. Moret, R. Currat, J. Dianoux,

Advanced NMR Techniques and Applications

Incoherent-neutron-scattering measurements of the vibrational density of states of acetanilide and three deuterated derivatives are presented. These data allow one to identify an intense maximum, assigned to the N-H out-of-plane bending mode. The data display the specific behavior of the methyl torsional modes: large isotopic shift and strong low-temperature intensity; confirm our previous inelastic-neutron-scattering studies, indicating no obvious anomalies in the range of frequency of the acoustic phonons. In addition, the data show the existence of thermally activated quasielastic scattering above 100 K, assigned to the random diffusive motion of the methyl protons. These results are discussed in the light of recent theoretical models proposed to explain the anomalous optical properties of this crystal.