Laser-Ionization of Energetic Compounds: Differences and Similarities between Structures and Energetics of Gaseous Monomers and Solid State

As one of the processes following pulsed nanosecond or ultrafast laser ablation of solids, ionization is expected to direct molecular dissociation events. Ionization-induced effects on the RDX(s) and RDX (g) are computationally investigated using DFT methods and normal mode displacement calculations incorporating the Duschinsky effect. Structures, dissociation enthalpy and free energies of the resulting [(RDX)₂]⁺ clusters show that ionization caused 75% of the conformers to be unstable in their neutral isomeric composition and orientation. 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 the charged moieties, causing the greatest stabilization. The energy costs of ion-neutral dissociation are comparable to the hydrogen-transfer and NO₂ loss processes. The RDX conformational identity is a determining factor in the emerging dissociation pathways in both dimeric and monomeric forms. Ionization of the RDX surface is proposed as another source of NO₂ and HONO precursors of the NO⁺ ion observed previously.