IR,UV and visible absorption of X irradiated single crystals of sodium nitrite

X irradiation of NaNO₂ single crystals, induces a motion of some NO₂^? ions, mainly around the axis perpendicular to their planes (a axis). The change in the orientation of NO₂^? is observed on the v₂ vibration of NO₂^? (by IR absorption) and on the vibronic structures associated with the NO₂^? electronic transitions (by UV and visible absorption). Other centers, like no₃^?, are also produced by irradiation. Their evolution with temperature is studied.