The spectra of the crystals of pyridine picrate crude formula, C11H8N4O7, in the mid infrared (IR) and Raman are studied as a function of temperature. They show some changes, which allowed us to first track and describe the structural changes (in both directions under the effect of heat treatment) accompanying the phase transition between 358 and 383K observed by DSC, Rx. After gradual cooling, the reversibility of the alteration may be detected by the variation 1'etude frequencies and relative heights of the lines connected to groups of bands NO2, NH and CH. The results show that the transformation kinetics is influenced by the operational conditions.
Key words: Picrate pyridine transition phase, reversibility, infrared (IR), Raman, X-ray diffraction (XRD).