Laser ionization of solid RDX: a density functional theory study

Abstract

Structural changes induced via ionization in an RDX lattice have been studied by using optimized [(RDX)2]0 conformers comprising eight combinations of four RDX isomers using DFT. Structures, dissociation enthalpy, and free energies of the resulting [(RDX)2]·+ clusters are calculated. The gas-phase and medium polarizable continuum model (PCM) calculations of the most stable [(RDX)2]·+ cluster produced similar structural results. Electron removal caused 75% of the [(RDX)2]·+ conformers to be unstable in their neutral isomeric composition and orientation. Charge distributions and structural factors indicate that [(RDX)2]·+ are in the general form RDX·+·RDX. Ionization causes charge polarization, hydrogen transfer, N-N dissociation, and assisted HONO formation in solid RDX. The assisted HONO formation occurs via and suggests hydrogen mobility within [(RDX)2]·+, causing a stabilization by a minimum of 114 kJ/mol more than the other conformers. The RDX conformational identity is a determining factor in the emerging dissociation pathways. The energy costs of ion-neutral dissociation are comparable to the hydrogen transfer and NO2 loss processes. Ionization of the RDX surface is expected to produce NO2 and HONO precursors of the NO+ ion observed previously.