The changes in Raman CH3 rocking spectra of aqueous tetraethylammonium bromide (Et4NBr) solution have been measured both in the liquid and glassy states as a function of water concentration. It is remarkable that, for the concentration region having the double glass transition temperatures (T-g) due to the liquid-liquid immiscibility (phase separation), the concentration dependence for the relative intensities of the trans trans. trans-trans and trans-gauche. trans-gauche conformers of tetraethylammonium (Et4N+) ions in the glassy state shows irregular behavior. Here, we show the possible cause for the phase separation of Et4NBr solution in the glassy state. (c) 2005 Elsevier B.V. All rights reserved.