Emission and fluorescence spectroscopy to examine shock-induced decomposition in nitromethane

Time-resolved emission spectra were obtained from neat and ethylenediamine-sensitized nitromethane shocked to 12-17 GPa peak pressures using step wave loading. Broadband emission identified as chemiluminescence from nitrogen dioxide was observed due to reactions in both neat and amine-sensitized nitromethane. When laser light at 514 nm was present, fluorescence in addition to chemiluminescence was observed in shocked nitromethane-ethylenediamine mixtures; no such fluorescence was found in neat nitromethane. The fluorescing species are assigned to an intermediate formed in the first stage of decomposition in nitromethane-ethylenediamine mixtures. The same intermediate was detected previously using time-resolved optical absorption spectroscopy (J. Phys. Chem. A 1998, 102, 2322) and was inferred to be a radical anion of nitromethane, CH3NO2.-. This interpretation is consistent with the fluorescence data reported here. Laser irradiation (similar to 10 MW/cm(2) at 514 nm) during shock loading resulted in more intense chemiluminescence in both neat nitromethane and nitromethane-ethylenediamine mixtures. However, the effect was qualitatively different in the two cases, and the difference is attributed to different decomposition mechanisms operative initially in neat and sensitized nitromethane.