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Computational study of the decomposition mechanisms of ammonium dinitramide in the gas phase

ABSTRACT CBS-QB3 method has been employed to determine the geometries, the vibrational frequencies of the reactants, the products and the transition states involved in intramolecular hydrogen-transfer and decomposition reactions of the free gas-phase H3N···HN(NO2)2 (ADN*). The results show that the intramolecular hydrogen-transfer reaction of ADN* is more feasible than that of HDN. ADN* and its hydrogen-transfer isomers ADN*-IIa,b,c decompose along four channels to form NH3 + HONO + 2NO (PI), ȮH + ṄO3 + N2 + NH3 (PII), ȮH + ṄO2 + N2O + NH3 (PIII), and HNO3 + N2O + NH3 (PIV), respectively. It has been found that the dominant decomposition channels are PI and PIII. The hydrogen-transfer reaction can reduce the barrier of elimination of NO2 and forming N2O reactions in ADN* and HDN. The decomposition of ADN*-IIc to form NO2 and N2O is more feasible than that of the gas-phase HDN. The rate constants (k) of rate-determining step of ADN* show that kPI and kPIII are higher than kPIV and kPII. Compared with HDN-IIc → N2O+ȮH+ṄO2, kPIII of ADN*-IIc is significantly higher than that of kHDN-IIc. These results reveal that NH3 (as a chaperon) has a certain influence on the decomposition mechanisms and kinetics of ADN*.