EPR evidence for the restricted mobility of NO2 in gamma irradiated thorium nitrate pentahydrate Th(NO3)4·5H2O

► The EPR spectrum gave evidence for the stabilization of NO2 in at least three different sites slightly differing in their geometries. ► The NO2 molecule at Site1 present at interstitial sites or those adsorbed on the surface exhibits mobility with increase in temperature above 100 K. ► The mobility is attributed to the preferred rotation of NO2 molecule about the O-O bond direction. ► The NO2 molecule at Site2 was found to be rigid as it was bound to thorium through two oxygen atoms or to thorium on one side through one oxygen atom and hydrogen bonded to water on the other side.