Despite decades of research, the chemical processes and states of matter that govern the behavior of energetic materials under detonation conditions are not well understood, including the molecular-level processes that determine decomposition kinetics and energy release. Oxygen content is often employed as a simple and intuitive guide to the development and practical use of explosives, but its effect on detonation chemistry remains little studied, especially for the case of oxygen overabundance. To this end, we have conducted quantum molecular dynamics (QMD) simulations of zero oxygen balance and oxygen-rich mixtures of hydrogen peroxide and nitromethane under detonation-like conditions to near-equilibrium time scales. We find excellent agreement between our extrapolated chemical equilibrium properties and those from thermochemical models for the zero oxygen balance mixture. In contrast, for the oxygen-rich mixture, we observe the formation of nitrogen oxide intermediates, particularly nitrate ions (NO3), that effectively act as an oxygen/nitrogen "trap" by precluding the formation of the equilibrium products N-2 and CO2. Our results could have implications for the design and modeling of oxygen-rich energetics in common military and industrial use.