A detailed IR study of the order–disorder phase transition of NaNO2

The infrared spectra of sodium nitrite NaNO2 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 NaNO2 by clear variations obtained in the spectral parameters for the bending modes ν2 (≈830 cm−1) asymmetric stretching mode ν3 (≈l270 cm−1) and combination mode (ν1+ν3) (≈2552 cm−1). The rotational energy barrier for the nitrite group NO2 is determined for both ordered and disordered phases using ν2 and ν3 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.