Brillouin scattering from transverse phonons in a molecular liquid and in an ionic salt melt mixture - a comparison

We compare in this report the Brillouin spectra of transverse (TA) phonons in two very different glass-forming systems above the glass transition temp erature T-g. The first system is the fragile molecular van der Waals liquid m-tricresyl phosphate (mTCP), while the other is the (mainly) ionic salt m elt mixture (NaPO3)(0.94)(Al(PO3)(3))(0.06), which is of intermediate fragi lity. The depolarized spectra of mTCP show a pronounced orientational line beside the TA modes. We analyse the spectra using the theoretical ansatz (D reyfus et al., 1998, Europhys. Lett., 42, 55) which produces the TA spectra l shape from a rotation-translation coupling mechanism. The salt melt gives rise to only a weak unresolved central line. The spectral shapes of the ph onons are similar as predicted by the ansatz given in Dreyfus er nl. (1998) . We believe we see here, for the first time experimentally, a transverse l ine shape, which consists of a propagating part, as usual, but also shows a 'Mountain'-like non-propagating part, which is known to exist for density waves.