A melting point of N3PA could not be determined because an explosion occurred at 68 °C. This is in line with the results of our molecular-beam mass spectrometer (MBMS) experiment (Figure ); N3PA was heated under vacuum and the released molecules analyzed by mass spectrometry. We observed a strong increase in signals for PN (m/z = 45), N2 (m/z = 28) and A (m/z = 178 and smaller fragments) already at around 42 °C in the chromatogram as a single strong peak that is clear evidence for an explosive decomposition. Gaseous PN is reported to polymerize very easily and form white powder coatings on surfaces and spectroscopic windows. We assume that the polymerization process might also contribute significantly to the observed explosion in our melting point determination. The surface of the sealed capillary was also covered with a white powder coating after the explosion occurred. Phosphorus triazide (P(N3)3) was reported to decompose smoothly in solution at room temperature with liberation of nitrogen, accompanied by the appearance of a strong 31 P resonance at δ 16.2 ppm and a weaker one at δ 6.2 ppm. However, these two signals were not assigned at all but an assignment to the free PN molecule could be excluded. Similar to many other reported P(III) azides, N3PA decomposes smoothly in solution at room temperature under standard conditions. Consequently, we followed the decay of N3PA in benzene-d6 by H NMR spectroscopy (Figure -S23, Table -S2). The azide decomposes at 25.0 °C with a first order kinetics half-life of around half an hour (t1/2 = 29.1 ± 1.6 min) and no new resonances appear in the 31 P NMR spectrum. Instead we observed the formation of yellow-orange-brown material in our NMR tube that is line with previously reported PN polymerization products; note that the color of the polymer changes depending on the nitrogen content. Further kinetic measurements on N3PA decomposition were performed over the temperature range of 25-55 °C. An Eyring analysis revealed activation parameters of ΔH ⧧ = 19.5 ± 1.7 kcal mol -1 and ΔS ⧧ = -8.8 ± 0.8 cal mol -1 K -1 (Figure ). The first-order behavior is indicative of a unimolecular rate-determining step, consistent with fragmentation of N3PA into N2, PN and A.