Ab Initio Chemical Kinetics for Nitrogen Tetroxide Reactions with 1,1‐ and 1,2‐Dimethylhydrazines

Abstract

AbstractThis work employed the quantum‐chemical method at the CCSD(T)/6‐311+G(3df,2p)//B3LYP/6‐311+G(3df,2p) level to study the mechanisms and kinetics of N2O4 (NTO) with H2NN(CH3)2 and CH3NHNHCH3 hypergolic initiation reactions, the processes critical to the chemical rocket propulsion of the N2O4‐hydrazine propellant systems. The reaction of N2O4 with the dimethylhydrazines (DMHZ's) can be started by the fast reaction of DMHZ's with ONONO2, taking place after the novel N2O4→ONONO2 transformation with each of DMHZ's as a spectator within the NTO‐DMHZ collision complexes, through loose, roaming‐like transition states during the bimolecular encounters. The barriers for such isomerization processes were found to be 7.2 and 9.9 kcal/mol for H2NN(CH3)2 and CH3NHNHCH3, respectively. The kinetics of these reactions have been computed in the temperature range 200–2000 K; the results indicate that under the ambient temperature and pressure condition, the half‐life of NTO in the presence of an excess amount of H2NN(CH3)2 is predicted to be 3.3×10−5 s. The results of a similar estimate for CH3NHNHCH3 is about 2 orders of magnitude longer; both estimates indicate that very effective hypergolic reactions can occur upon mixing in these systems.