Nitrogen-Nitrogen Bond Breaking in Irradiation Products of Hexanitrohexaazaisowurtzitane (CL-20)

While the primary result of an interaction of ionizing radiation with an organic material is the ejection of electrons from molecular orbitals producing cations, the free electrons can further interact, yielding excited states; and, potentially, anions. In this work, we computed reaction barriers and energies for N-N bond breaking in the CL-20 cation, anion, and excited state to investigate if CL-20 degradation is accelerated after radiation exposure. We focused on N-N bond dissociation because it is the rate-determining step in the thermal degradation of CL-20. We found that N-N cleavage rapidly takes place in the CL-20 cation and anion with greatly reduced reaction energies as compared to CL-20. We also outlined a potential path for photodissociation of the N-N bond. While CL-20 is kinetically stable, initial degradation occurs readily in its irradiation products. This is of importance for the performance of the explosive after high-dose exposure and influences aging if CL-20 is irradiated at a low dose over extended periods of time.