Theoretical investigation on the interaction of hypergolic monomethylhydrazine with 1-chloro-1,1-dinitro-2-( N -chloroamidino)ethane using DFT methods

Abstract

The reaction mechanism underlying the hypergolic reaction of pure monomethylhydrazine (MMH) with 1-chloro-1,1-dinitro-2-(N-chloroamidino)ethane (CDNCE) was theoretically investigated with the density functional theory method. We identified two key atomistic level factors that affect ignition delay: (1) exothermicity for the formation of aerosol mCDNCE·nMMH complexes (m, n = 1, 2). The most cost-effective form was found to be 2CDNCE·MMH with the highest energy release (releasing energy: 23.4 kcal/mol), indicating that the oxidizer-rich form is favorable. These complexes contributed the most to heat gathering and temperature increases in the system at the beginning of all reactions. (2) For the initial reaction of MMH with CDNCE, the S_N2 mechanism was preferred. The activation barrier of the primary reactions was calculated to be 27.4 kcal/mol, which is also the rate-limiting step of this path. Because the rate of formation of NO₂ was four orders of magnitude lower than the S_N2 reaction at room temperature, the effect of MMH with NO₂ was less significant at temperatures below 800 K. Thus, we consider the ignition reaction of MMH with CDNCE to be well characterized.