The phonon dispersion curves for the 12 external and the four lowest internal modes in d8-naphthalene (C10D8) have been determined at 6K for the ( xi ,0,0), (0, xi ,0), (0,0, xi ), (1/2, xi ,0) and ( xi , xi ,0) directions by coherent inelastic neutron scattering. The results agree very well with optical data. Calculations performed in the harmonic approximation for the rigid-molecule model based on the atom '6-exp' potential were carried out beforehand to produce inelastic structure factors, which turned out to be very useful in the experimental work. This model predicts the qualitative behaviour of the dispersion curves surprisingly well, although some frequencies do differ by 20%. The experimental results show many mode-mixing and anticrossing effects. The present results should serve as a basis for improvements on the model.
I. Natkaniec, E. L. Bokhenkov, B. Dorner
Journal of Physics C: Solid State Physics