Through the use of simultaneous thermogravimetry modulated beam mass spectrometry measurements, time-of-flight velocity-spectra analysis, and {sup 2}H, {sup 13}C, {sup 15}N, and {sup 18}O labeled analogues of 1,3,5-trinitrohexahydro-s-triazine (RDX), the thermal decomposition products of RDX have been identified as H{sub 2}O, HCN, CO, CH{sub 2}O, NO, N{sub 2}O, NH{sub 2}CHO, NO{sub 2}, HONO, (CH{sub 3})NHCHO, oxy-s-triazine (OST), and 1-nitroso-3,5-dinitrohexahydro-s-triazine (ONDNTA) and all of their gas formation rates have been measured as a function of time. From these results the primary reaction pathways that control the decomposition of RDX in both the solid and liquid phases have been discovered. Four primary reaction pathways control the decomposition in RDX. One produces predominantly OST, NO, and H{sub 2}O and accounts for about 30% of the decomposed RDX, and the other produces predominantly N{sub 2}O and CH{sub 2}O with smaller amounts of NO{sub 2}, CO, and NH{sub 2}CHO and accounts for 10% of the decomposed RDX. The third pathway consists of formation of ONDNTA by reaction between NO and RDX, followed by the decomposition of ONDNTA to predominantly CH{sub 2}O and N{sub 2}O. The fourth reaction pathway consists of decomposition of RDX through reaction with a catalyst that is formed from the decomposition productsmore » of previously decomposed RDX. The third and fourth reaction channels each account for approximately 30% of the decomposed of RDX. Experiments with solid-phase RDX have shown that its decomposition rate is very much slower than that of liquid-phase. ONDNTA is the only product that appears to be formed during the early stages of decomposition of RDX in the solid phase. 34 refs., 10 figs., 4 tabs.« less