Light scattering and dielectric susceptibility spectra of glassforming liquids

We propose a simple explanation for the marked difference in the spectral shapes of the dielectric and the depolarized light scattering susceptibilities of the fragile molecular glassforming liquids: it is the direct consequence of the probing of the same molecular orientational dynamics through techniques having different tensorial properties. We deduce a relationship between the corresponding nonergodicity parameters which is well verified in molecular dynamics simulations available so far. We also show that the corresponding orientational susceptibilities of the NO(3)(-)ions in the glassformer CKN, obtained in a recent simulation, exhibit the same spectral difference as in the molecular liquids.