Vibrational Spectrum and Force Field of Ruthenium Tetroxide

Abstract

Infrared and Raman spectra are reported for the vapor and liquid phases of Ru16O4 and Ru18O4. Anharmonicity corrections were estimated for the observed isotope shifts, and Coriolis constants were obtained from the infrared band contours. General quadratic force constants are calculated, using as constraints the 16O–18O and 96Ru–102Ru isotope shifts, Coriolis constants, and vibrational amplitudes; the relative effectiveness of these and the effects of the anharmonicity corrections are discussed. The force field is nearly extremal. The valence stretching force constant is fr = 6.99±0.04 mdyn/Å, appreciably less than for OsO4. Standard-state thermodynamic functions for RuO4 vapor are calculated for the temperature range 273–500°K.