Infrared and Raman spectra of MoO3 molybdenum trioxides and MoO3 · xH2O molybdenum trioxide hydrates

The infrared and Raman spectra of powder samples of MoO3 (orthorhombic and monoclinic) and of MoO3 · xH2O (x = 13, 12, 1 and 2) have been recorded and the most characteristic frequencies are discussed with reference to the available structural data and to previous vibrational assignments. A qualitative assignment is given in terms of group frequencies for the stretching vibrations of units involving oxygen atoms linked to one, two or three molybdenum atoms and a correlation is established between bond length and stretching force constant. In the case of the hydrates, partial deuteration allows the symmetry of the water molecules to be determined. Characteristic hydrogen bond distances are evaluated from the frequencies of the isolated HOD stretching vibrations.