Theoretical insight into the structure and stability of TNT and RDX in external electric field

Abstract

A comparison of the effect of external electric field on the C–NO₂ or N–NO₂ bonds with the C–H and N–O bonds in 2,4, 6-trinitrotoluene (TNT)or hexahydro-1,3,5-trinitro-s-triazine (RDX) has been carried out using the M06-2x method with the 6-311++G** and aug-cc-pVTZ basis sets. The result shows that for TNT the fields have a minor effect on the C–NO₂ and C–H bonds but a major effect on the N–O bonds, while in RDX the fields greatly affect the N–NO₂ bond but the N–O and C–H bonds are slightly affected. Thus, in TNT the N–O bond can be the trigger bond, and in RDX the N–NO₂ bond is always the trigger bond in electric fields. The explosive sensitivities may be reduced and the stabilities may be increased under the external electric fields in the negative direction along the C–NO₂ bond axis for TNT and in the positive direction along the N–NO₂ or N–O bond axis for RDX. The opposite trends can be suggested in the fields of the opposite directions along above bond axes. The introduction of external electric field into energetic material may be an available way to adjust explosive sensitivity. The analyses of AIM (atoms in molecules) and frequencies support the above viewpoints. The linear correlations between the field strengths and the changes of N−O/N−N bond lengths, ρ_{(N−O/N−N)} values, or stretching frequencies of the N−O/N−N bonds have been found.