Thermal decomposition of condensed nitromethane from molecular dynamics using the ReaxFF Reactive force field

We study the thermal decomposition and subsequent reaction of the energetic material nitromethane (CH$_3$NO$_2$) using molecular dynamics (MD) with the ReaxFF first principles-based reactive force field. We characterize the chemistry of liquid and solid nitromethane at high temperatures (2000-3000 K) and density 1.97 g/cm$^3$ for times up to 200 picosec. At T=3000 K the first reaction in the decomposition of nitromethane is an inter-molecular proton transfer leading to CH$_3$NOOH and CH$_2$NO$_2$. For lower temperatures (T=2500 and 2000 K) the first reaction during decomposition is often an isomerization reaction involving the scission of the C-N bond the formation of a C-O bond to form methyl nitrate (CH$_3$ONO) . Also at very early times we observe intra-molecular proton transfer events. The main product of these reactions is H$_2$O, which starts forming following the initiation steps. The appearance of H$_2$O marks the beginning of the exothermic chemistry. Recent quantum mechanics-based MD simulations on the chemical reactions for a crystalline sample heated to T=3000 K for 10 ps are in excellent agreement our ReaxFF MD, providing a direct validation of ReaxFF.