Quantum chemistry calculations reveal that it is both thermodynamically and kinetically feasible for NO2 to be oxidized by RDX (1,3,5-trinitrohexahydro-s-triazine) or its initial decomposition products. Thus, NO3 (nitrate radical) may be produced during the thermal decomposition of RDX and other nitramines. However, experimental studies of the gaseous products, by mass spectrometry and microwave spectroscopy, have never detected NO3. This fact is reconciled with the calculations by noting that (1) the electron-impact, positive-ion mass spectrum of NO3 shows little parent ion, (2) NO3 lacks a permanent electric dipole moment and is therefore invisible to microwave spectroscopy, and (3) NO3 is quite reactive. Further experiments are encouraged and could lead to a new method for detecting concealed nitramines.