Raman phonon spectroscopic study of phase transition in o-aminobenzoic acid crystal (II)

Raman phonon spectroscopy in the 10-150 cm -1 shift range was used to study the phase transition in an o-aminobenzoic acide crystal (II). At 77 K, twelve distinct phonon modes are observed whereas at 300 K the spectrum shows ten phonon bands. The temperature dependence of the phonon frequencies and band withs suggest that the crystal goes through a phase transition at ca. 200 K. The temperature dependence of the internal modes predicts that the phase transition is associated with some structural change in the phenyl ring