A Vacuum Ultraviolet Photoionization Study on the Isomerization, Decomposition, and Molecular Mass Growth Processes in Solid Nitromethane (CH3NO2)

Abstract In this Feature Article, we highlight the crucial findings from experimental and theoretical studies investigating the dissociation mechanisms of condensed phase nitromethane (CH3NO2), a model compound of nitro-hydrocarbon (R-NO2) based energetic material. Our findings on intriguing isomerization, decomposition and molecular mass growth pathways of nitromethane are placed into perspective by exploiting complementary spectroscopy probes such as Fourier Transform Infrared Spectroscopy (FTIR), Electron Paramagnetic Resonance (EPR), and single-photon isomer selective photoionization reflectron time-of-flight mass spectrometry (PI-ReTOF-MS) in conjunction with quantum chemical calculations. These investigations unravel the isomerization of nitromethane to exotic isomers such as aci-nitromethane, nitrosomethanol, and N-hydroxyoxaziridine. Evidence of non-equilibrium decomposition channels involving suprathermal oxygen, hydrogen and carbene formation are also revealed. Finally, involvement of these radical species in molecular mass growth processes leading to higher molecular weight products are emphasized. Benchmark studies established from a ‘simple’ nitromethane system are highly beneficial to predict the decomposition mechanisms of ‘real’ explosives.