Temperature Dependent Variations of Phonon Interactions in Nanocrystalline Cerium Oxide

The temperature dependent anharmonic behavior of the phonon modes of nanocrystalline CeO2was investigated in the temperature range of 80–440 K. The anharmonic constants have been derived from the shift in phonon modes fitted to account for the anharmonic contributions as well as the thermal expansion contribution using the high pressure parameters derived from our own high pressure experimental data reported previously. The total anharmonicity has also been estimated from the true anharmonicity as well as quasiharmonic component. In the line-width variation analysis, the cubic anharmonic term was found to dominate the quartic term. Finally, the phonon lifetime also reflected the trend so observed.

The Gas-phase Structure of the Hexasilsesquioxane Si6O9(OSiMe3)6

The equilibrium molecular structure of the hexasilsesquioxane, Si6O9(OSiMe3)6, has been determined in the gas phase by electron diffraction. With OSi-containing substituents on the cage silicon atoms, this molecule closely resembles the moiety that if reproduced in a periodic manner would yield a zeolite-type structure. Semi-empirical molecular-dynamics (SE-MD) calculations were used to give amplitudes of vibration, vibrational distance corrections (differences between interatomic distances in the equilibrium structure and the vibrationally averaged distances that are given directly by the diffraction data) and anharmonic constants. A number of different SE-MD methods were tested, and their results are compared. The inclusion of d-type orbitals in the SE-MD method is crucial for obtaining accurate vibrational quantities for Si6O9(OSiMe3)6, with the PM6 and MNDO/D methods both giving acceptable values

Centres de bandes et constantes d'anharmonicité de la molécule du trifluorure de phosphore PF3

In this paper, we establish interesting relationships linking rovibrational band-centers and anharmonic constants of symmetric top molecule. Using these relationships, nine accurate values of the xij and gij anharmonic constants have been deduced from the band-centers of fundamental, overtone, combination, and hot bands of the PF3 gas molecule. Taking into account the Fermi resonance between the ν3 and ν2 + ν4 bands, with a W234 = 2.86 cm–1 coupling term, the band-centers and the anharmonic constants of the molecular potential have been corrected.