Structural and Dynamical Insights from Vibrational Multipolar Analyses of Isotropic Media: Application to Molecular Liquid CCl4 and Silica Glass SiO2

Abstract

We propose and describe combined multipolar vibrational decompositions of IR, polarized Raman and hyper-Raman spectra as a powerful method to study and interpret vibrational spectra in isotropic materials. We have applied this new method to the molecular liquid CCl4 and to silica glass, which are both made of elementary tetrahedral units weakly interacting and strongly 3D-linked, respectively. As expected, huge deviations of vibrational multipolar activities from isolated tetrahedron are observed in silica glass. From the vibrational multipolar analyses, we propose a structural model, beyond the local tetrahedral unit, because it encompasses first neighborhoods, which fits the activities of the multipolar vibrational spectra. It is derived from the unit cell of the α-cristoballite structure, with an octupolar S4 symmetry, which consists of a central SiO4 tetrahedron embedded in a super Si4/4 tetrahedron with bent Si−O−Si bonds.