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 temperature 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 melt mixture (NaPO3)(0.94)(Al(PO3)(3))(0.06), which is of intermediate fragility. The depolarized spectra of mTCP show a pronounced orientational line beside the TA modes. We analyse the spectra using the theoretical ansatz (Dreyfus et al., 1998, Europhys. Lett., 42, 55) which produces the TA spectral shape from a rotation-translation coupling mechanism. The salt melt gives rise to only a weak unresolved central line. The spectral shapes of the phonons 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 line 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.