Spectre d'absorption dans l'infrarouge lointain (15–250 cm −1) d'un cristal d'acide salicylique a temperature de l'azote liquide (80 K)

Abstract

Comparison of absorption spectra of salicylic acid in the crystal state and in solution leads to a division of the spectrum into external frequencies lower than 92 cm −1 and internal frequencies higher than 125 cm −1 at 300 K. The external frequencies are ascribed to translational vibrations of the two dimers in the unit cell at 37.5, 47 and 54 cm −1, and to torsional vibrations of the dimers coupled either symmetrically or antisymmetrically. The determinations are made on consideration of the crystal trichroïsm in the far IR and on calculation of relative intensities of the torsional vibration absorption bands on the three observed directions.