Structure and charge density distribution of amine azide based hypergolic propellant molecules: a theoretical study

Abstract

A quantum chemical calculation and charge density analysis of some amine azide based propellants (DMAZ, DMAEH, ADMCPA, AMCBA and ACPA) have been carried out to understand the geometry, bond topological, electrostatic, and energetic properties. The topological properties of electron density of the molecules were determined using Bader’s theory of atoms in molecules from the wave functions obtained from the density functional method (B3LYP) with the 6-311G** basis set. The electron density distribution of these molecules reveals the nature of chemical bonding in the molecules. The azide group attached C−N bonds of all molecules exhibit the electron density of ρbcp(r) ∼1.639 e Å−3 and the Laplacian of electron density ∇2ρbcp(r) is ∼–14.0 e Å−5, in which the corresponding values of the ADMCPA molecule are relatively high, 1.725 e Å–3 and –15.2 e Å−5 respectively, whereas for the methylamine group attached C–N bonds, these values are found to be higher (1.824 e Å–3 and –17.25 e Å−5). The Laplacian of terminal N–N bonds of the azide group is highly negative, indicating that these charges are highly concentrated, whereas the charge concentration of the dimethylamine group attached N–N bond of DMEAH is very much less, confirming that the bond is the weakest bond among the molecules. The energy density has been calculated for each bond of the molecules, which insights the energy density distribution of the molecules. Relatively, the molecules exhibit distinct electrostatic properties that are related to different charge distribution in the molecules. Large negative electrostatic potential regions are found at the vicinity of the amine and azide groups of the molecules. The charge imbalance parameter of the molecules has been determined and shows that the DMAEH molecule is the least sensitive molecule in this series.