Thermal decomposition of ammonium dinitramide proceedsvia homolytic rupture of the N−NO2 bond and partially by the proton transfer reaction. The monomolecular decay of the anion to N2O and NO3 − in the solid state at 60 °C occurs with higher rates than those in the melt. This is related to a change in the reactivity of the anion due to the violation of its symmetry on going to the solid state. The absence of hydrogen bonds between the anion and cations or water molecules is an additional condition for the fast decay.