Why mixtures of hydrazine and dinitrogen tetroxide are hypergolic?

Abstract

The reactions of N2H4 with N2O4 isomers have been investigated at the G2M(CC3)//B3LYP/6311++G(3df,2p) level. The results show that the reactions of N2H4 with sym-N2O4 (D-2h), cis-ONONO2 (C-s), and NO2 have to overcome 14.2, 10.6, and 7.6 kcal/mol barriers, respectively. However, N2H4 can react spontaneously with trans-ONONO2 (C-s) and cis-ONONO2 (C-1) to produce HONO2 + H2NN(H)NO with the near gas-kinetic rate constant, 4 x 10(-10) cm(3) molecule(-1) s(-1) above 250 K. The H2NN( H) NO thus formed can rapidly fragment to give reactive N2H3 radical with rate constant > 1 x 10(7) s(-1) at 1000 K, which is fast enough to initiate the hypergolic chain reactions with NO2 and N2O4. (C) 2012 Elsevier B.V. All rights reserved.