AVS 50th International Symposium
    Homeland Security Topical Conference Wednesday Sessions
       Session HS-WeP

Paper HS-WeP2
Temperature-Dependent micro-Raman Study of Some High Explosives

Wednesday, November 5, 2003, 11:00 am, Room Hall A-C

Session: Poster Session on Science & Technology for Homeland Security
Presenter: E.S. Etz, National Institute of Standards and Technology
Authors: E.S. Etz, National Institute of Standards and Technology
S.V. Roberson, National Institute of Standards and Technology
G. Gillen, National Institute of Standards and Technology
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In collaboration with the Transportation Security Agency, NIST has initiated a chemical metrology program that will support the nationwide operational deployment and utilization of trace explosives detection devices. The project critically examines the analytical methodology whereby collections of micrometer-sized high explosives (HE) particles undergo thermal vaporization at the front-end of an ion-mobility spectrometer (IMS), leading to sample detection and identification. We have started to examine this front-end process in detail with a focus on particle transport and HE thermalization-vaporization for the IMS detection system. Of interest here is the temperature behavior and the thermochemistry of the analyte HEs in the temperature regime leading to the melting point, and beyond to the vapor phase. To understand the fragmentation and decomposition of HEs, we are using Raman microspectroscopy to study the particle spectra of relevant HEs heated to their melting temperature, and beyond, on a microscope hot-stage. The spectra are examined for (i) shifts in the peak frequency of Raman bands, (ii) temperature-induced changes in the spectral halfwidth and asymmetry of bands, (iii) changes in the relative intensities of bands and (iv) the presence of decomposition products. The spectra are acquired with a commercial Raman microprobe utilizing 514.5, 532, and 785 nm excitation. Discussed are the results obtained for the explosives TNT (m.p. 80.7 °C), PETN (m.p. 141.3 °C), RDX (m.p. 204 °C), and the plastic binary composites Semtex and C-4. The spectra show considerable changes as the sample is ramped up to the higher temperatures. These changes take on various forms, including substantial peak shifts to lower frequencies, band broadening with lowering of symmetry, and pronounced relative intensity changes. These spectral manifestations are correlated with the structural and compositional changes of these organic samples.