The orientation and vibrational states of H2O in synthetic alkali-free beryl

The polarized single-crystal Raman spectra of synthetic H2O-containing alka li-free beryl were recorded at room and low temperatures, and the polarized single-crystal IR spectra at room temperature. The H2O molecule in the cha nnel cavities is characterized by a Raman-active symmetric stretching vibra tion (nu(1)) at 3607 cm(-1) and an IR-active asymmetric stretch (nu(3)) at 3700 cm(-1) at room temperature. At low temperatures this nu(3) mode is obs erved in the Raman. Weak nu(1) and nu(3) modes of a second type of H2O are also observed in the Raman spectra but only at 5 K. The H ... II vector of the most abundant type of H2O is parallel to the channel axis of beryl alon g [0 0 0 1]. The components of the polarizability tensor of the vl mode of H2O are similar to, but not exactly the same as, those of a free H2O molecu le, The Raman measurements indicate that the H2O molecule is rotationally d isordered around [0 0 0 1]. External translation and librational modes of H 2O could be observed as overtones with the internal H2O-stretching modes. I n the case of the librational motions, normal modes could also be observed directly in the Raman spectra at similar to 200 cm(-1). The energies of the translational modes can be determined from an analysis of the overtones an d are about 9 cm(-1) in energy (i.e., T-z). The energies of the librational modes are about 210 cm(-1) for R-x and 190 cm(-1) for R-y.