Energetic Material Detection by Laser Photofragmentation-Fragment Detection

Report No. ARL-TR-5244
Authors: Stephen D. Roberson and Rosario C. Sausa
Date/Pages: August 2010; 28 pages
Abstract: We detect thin films of 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-hexanitro-1,3,5-triazine (RDX) by one- and two-laser photofragmentation (PF) with subsequent fragment detection in real time at ambient temperature and pressure. In the one-laser technique, a laser tuned to 226 nm excites the energetic material and both generates the characteristic nitric oxide (NO) photofragments and facilitates their detection by resonance-enhanced multiphoton ionization (REMPI) using their A-X (0,0) transitions near 226 nm. In contrast, in the two-laser technique, a 454-nm laser generates the analyte molecule in the gas phase by matrix assisted desorption, and a second laser tuned to 226 nm both photofragments it and ionizes the resulting NO. We report the effects of laser energy, analyte concentration, and matrix concentration on the ion signal and determine the rotational temperatures of the NO photofragments from Boltzmann, rotational distribution analysis of the REMPI spectra. We achieve limits of detection (LOD) (S/N=3) of hundreds of ng/cm² for both techniques under ambient conditions with a positive signal identification as low as 70 pg using a single, 226-nm laser pulse of about 50 µJ.
Distribution: Approved for public release
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Last Update / Reviewed: August 1, 2010