Investigation of Shock-Induced Chemical Decomposition of Sensitized Nitromethane Through Time-Resolved Raman Spectroscopy

Abstract

Molecular processes associated with shock induced chemical decomposition of a mixture of nitromethane with ethylenediamine (0.1 wt%)are examined using time-resolved, Raman scattering. When shocked by stepwise loading to 14.2 GPa pressure, changes in the nitromethane vibrational modes and the spectral background characterize the onset of reaction. The CN stretch mode softens and disappears even as the N02 and CH 3 stretch modes, though modified, retain their identities. The shape and intensity of the spectral background also shows changes characteristic of reaction. Changes in the background, which are observed even at lower peak pressures of 11.4 GPa, are assigned to luminescence from reaction intermediates. The implications of these results to various molecular models of sensitization are discussed.

Optical Characterization of Chemistry in Shocked Nitromethane with Time-Dependent Density Functional Theory

“…In the specific cases of nitromethane and several other model energetic materials, a number of experimental observations of high-temperature and high-pressure chemistry have been reported. Equations of state, vibrational spectra, and optical spectra of stepwise shock-loaded nitromethane have been studied via time-resolved spectroscopy to determine details of the onset of chemistry. − Bouyer et al have performed optical emission spectroscopy on detonating nitromethane to measure the time-dependent temperature profile and the optical transparency spectrum of the products at and behind the shock front. − …”

Recent Developments to Understand Molecular Changes in Shocked Energetic Materials

“…In the following paragraphs, we summarize some of the important findings from our Raman measurements [17,19,22]. Further details will be presented elsewhere [22,34].…”

“…percent ethylenediamine) undergoes an irreversible change at peak pressures in the vicinity of 10 GPa (the exact threshold pressure has not been determined) [IS]. To investigate the molecular changes associated with the chemical decomposition in sensitized nitromethane, a series of Raman measurements were carried out in sensitized nitromethane [19,34]. Representative spectra of sensitized nitromethane shocked to 14 GPa are presented in Figure 3.…”