Modeling Decomposition of Energetically Functionalized Dodecanes

High explosives (HE) experience radiation in a variety of settings, from environmental sources to space applications. Degradation of HE in sunlight is also of interest. Understanding the decomposition of energetic functional groups (EFGs) in response to radiation is critical. Computational modeling provides a predictive view of HE degradation and reveals mechanistic details that can be difficult to obtain experimentally. We have designed a dodecane-X system, where X = H or the EFG azide, nitro, nitramine, nitrate ester. These molecules are investigated in order to obtain a systematic view of EFG degradation under UV radiation while keeping the molecular backbone constant. Dynamics following electronic excitation is modeled using the Non-Adiabatic Excited State Molecular Dynamics (NEXMD) software. NEXMD uses Fewest Switches Surface Hopping (FSSH) to model internal conversion. The open-shell configuration interaction singles (CIS) implementation coupled with the semi-empirical AM1 Hamiltonian accurately describes bond breaking barriers. An ensemble of trajectories is propagated allowing statistical determination of timescales (relaxation, bond breaking, and energy transfer) as well as quantum yields (QY), which are related to relative stability. We find that the primary low energy pathway involves only the EFG. The QY of the most probable pathway is generally reduced at higher energy as new pathways involving exciton energy transfer and decomposition of the alkane chain are introduced.