Mandelstam–Brillouin spectra and hyperacoustic velocities dispersion of trideuteroacetonitrile in the liquid state Original Research Article

Brillouin scattering spectra, as a function of temperature and transferred wave vector, were measured on deuterated acetonitrile. Its collective mode dynamics was compared with that of the light molecule, previously studied in this laboratory [P. Sassi, G. Paliani, R.S. Cataliotti, J. Chem. Phys. 108 (1998) 10197]. The results obtained in this study demonstrate that the hydrodynamic behaviour of the two isotopomers is quite similar. Small differences are observable at temperatures higher than 40°C. These differences regarding shear viscosity, adiabatic compressibility, sound absorption coefficient and thermal relaxation times, are discussed in terms of a local-structure relaxation in such molecular liquids. It concerns the local organization of small clusters of antiparallely aligned dipoles.