8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

P8.2Thu 811:10-14:00Hyperacoustic relaxations in liquids: a comparison ofrenormalized damped oscillator and generalizaedhydrodynamics approachesFrancesco Aliotta, 1 Rosina Celeste Ponterio, 1 Franz Saija, 1 Mikolaj Pochylski, 2and Jaceck Gapinski 21 Istituto per i Processi Chimico-Fisici CNR, Viale F. Stagno d’Alcontres 37, I-98158,Messina, Italy2 Faculty of Physics, Adam Mickiewicz Universty, Poznan, PolandThe two approaches commonly adopted to describe the Brillouin spectral density of liquids,namely based on generalized hydrodynamics and on the memory function respectively, are compared.It is shown that, contrary to the common belief, the two approaches are not fully equivalent.In particular, models based on the memory function of normalized damped oscillators fail in reproducingthe correct experimental spectral profiles of systems close to a relaxation process. Thesource of the discrepancy is individuated in an unavoidable mixing of spectral contributions at differentwave-vectors. Brillouin scattering data from supercooled water are presented and analyzedin the framework of the two different approaches.2