Sublimation studies of NpO2F2

Using Knudsen effusion mass spectrometry, we have identified the following reaction as the sublimation decomposition mechanism of NpO₂F₂(s): 2NpO₂F₂(s)=NpO₂(s)+O₂(g)+NpF₄(g). From second-law analysis of the measured pressures of NpF₄(g) over the temperature range 820-985 K the derived enthalpy change at 298 K is 556.8±12.2 kJ/mol and the entropy change is 342.4 ±13.8 J/K mol. From these values and enthalpies of formation and entropies reported in the literature for the other species we calculate the enthalpy of formation of NpO₂F₂(s) to be -1608±10 kJ/mol and the entropy to be 147±9 J/K mol.