Laser ionization of solid RDX: a density functional theory study

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 114kJ/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.