Normal coordinate analysis of the Raman and infrared vibrations of the alpha phases of RE₂O₃ (RELa, Pr, Nd) and RE₂O₂S (RELa and Yb)

A normal coordinate analysis of the spectra of the title compounds shows that they can be matched with a 6 force field. Metal‐O(S) force constants correlate approximately with bond length and range from 0.2 to 1.8 mdynes Å −1 . OO(S) force constants are less than 0.1 mdynes Å −1 but for a satisfactory fit a metal‐metal force constant of 0.5 mdynes Å −1 must be introduced. The infrared spectrum of Pr 2 O 3 is reported for the first time.