A detailed IR study of the order–disorder phase transition of NaNO 2

Abstract

The infrared spectra of sodium nitrite NaNO 2 have been investigated between 400 and 4000 cm −1 over a wide range of temperature (27–250°C). The results are reported during the order–disorder phase transition (II→I) at temperature about 161°C. The study includes spectral analysis and interpretation of band shape, peak height, band width and band intensities of the internal modes of vibrations as functions of temperature. The present results strongly confirm the phase transformation process from the ordered state II to the disordered state I of NaNO 2 by clear variations obtained in the spectral parameters for the bending modes ν 2 (≈830 cm −1) asymmetric stretching mode ν 3 (≈l270 cm −1) and combination mode ( ν 1+ ν 3) (≈2552 cm −1). The rotational energy barrier for the nitrite group NO 2 is determined for both ordered and disordered phases using ν 2 and ν 3 modes. Also, the phase transition process is found to be activated by an energy of 0.16 eV in the regions of these two modes.