Vibrational Multipolar Analyses in Isotropic Media: Combining IR, Raman and Hyper-Raman Spectroscopies

We introduce combined vibrational multipolar decompositions of IR, polarized Raman and hyper-Raman spectra as a powerful way to study isotropic materials. This new procedure has been applied to the molecular liquid HCCl3 and to silica glass, which are made of elementary structural units (ESU) weakly interacting and covalently 3D-linked, respectively. Through the vibrational multipolar analyses of these two different isotropic media, new structural and dynamical insights have been drawn. In particular, for silica we propose an ESU which fits the multipolar spectral activity. It is derived from the alpha-Cristoballite structure, with an octupolar S-4 symmetry, which consists of a central SiO4 tetrahedron embedded in a super Si-4/4 tetrahedron with bent Si-O-Si bonds.