Shock-Induced Chemical Changes in Neat Nitromethane:  Use of Time-Resolved Raman Spectroscopy

Time-resolved Raman spectroscopy was used to examine chemical changes in neat liquid nitromethane subjected to stepwise loading to peak pressures of 14−17 GPa. After a peak pressure at 14 GPa was reached, no changes in the CN (917 cm -1 ), NO 2 (1400 cm -1 ), and CH 3 (2968 cm -1 ) symmetric stretching modes were observed. After a peak pressure at 16 GPa was reached, time-dependent changes were observed during the induction period reported in previous absorption experiments. At this peak pressure, the extent of reaction was small, and the observed changes in the CH 3 and CN modes indicated prereaction changes in the sample bulk. After a peak pressure at 17 GPa was reached (980 K peak temperature), all three peaks disappeared, indicating that the extent of reaction was substantial under these conditions. The broadening of the CH 3 peak and the softening of the CN mode observed in this work suggest strong intermolecular interactions. These interactions lead to a reaction precursor involving proposed head-to-tail intermolecular associations with decomposition proposed to follow through a bimolecular reaction, put forward by Bardo, which forms nitrosomethane and nitromethanol. Confirmation of these ideas will require different spectroscopic methods, since Raman measurements are primarily useful for probing initial changes in the sample.