AbstractLow frequency polarized spectra were investigated from 300 to 30K; but, as accidental depolarization arises at low temperature, study was chiefly made at 300K. External vibrations have been assigned using group theory and the influence of hydrogen bonds on the motions of the molecular layers:Ag‐Bglibrations at 41.6–64.8, 83.5–42.4 and 130cm−1, translations in‐plane at 79 and 94, out‐of‐plane at 144 cm−1, owing to layers. Some infrared bands have been observ