Hildenbrand, D. L., Lau, K. H., & Chandra, D. (2010). Thermochemistry of gaseous ammonium nitrate, NH4NO3 (g). The Journal of Physical Chemistry B, 114(1), 330-332.
From the measured molecular weight of vapor over NH4NO3(c) by the simultaneous torsion-effusion/mass loss method, the partial pressure of NH4NO3(g) was evaluated over the range 321−360 K; in addition, the presence of the gaseous nitrate was verified by effusion-beam mass spectrometry. Third-law calculations of the sublimation enthalpy of NH4NO3 were made with estimated molecular constants, yielding ΔH298o(sub) = 20.9 ± 2 kcal mol−1, as compared to a less-reliable second-law value of 23.2 ± 3 kcal mol−1. We prefer the third-law value, which leads to the enthalpy of formation ΔfH298o (NH4NO3(g)) = −66.5 ± 2.1 kcal mol−1 when combined with the known ΔfH298o value of NH4NO3(c).