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

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 center dot center dot center dot 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 (P-I), (O) over dotH + (N) over dotO(3) + N-2 + NH3 (P-II), (O) over dotH + (N) over dotO(2) + N2O + NH3 (P-III), and HNO3 + N2O + NH3 (P-IV), respectively. It has been found that the dominant decomposition channels are P-I and P-III. 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 k(PI) and k(PIII) are higher than k(PIV) and k(PII). Compared with HDN-IIc -> N2O+ (O) over dotH+(N) over dotO(2), k(PIII) of ADN*-IIc is significantly higher than that of k(HDN-IIc). These results reveal that NH3 (as a chaperon) has a certain influence on the decomposition mechanisms and kinetics of ADN*. [GRAPHICS] .