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 degreesC). Th e results are reported during the order-disorder phase transition (II--> I) at temperature about 161 degreesC. The study includes spectral analysis an d interpretation of band shape, peak height, band width and band intensitie s of the internal modes of vibrations as functions of temperature. The pres ent results strongly confirm the phase transformation process from the orde red state II to the disordered state I of NaNO2 by clear variations obtaine d in the spectral parameters for the bending modes v(2) (approximate to 830 cm(-1)) asymmetric stretching mode v(3) (approximate to 1270cm(-1)) and com bination mode (v(1) + v(3)) (approximate to 2552 cm(-l)). The rotational energy barrier for the nitrite group NO2 is determined for b oth ordered and disordered phases using v(2) and v(3) modes. Also, the phas e transition process is found to be activated by an energy of 0.16 eV in th e regions of these two modes. (C) 2000 Elsevier Science B.V. All rights res erved.