Detection of Energetic Materials by Laser Photofragmentation/Fragment Detection and Pyrolysis/Laser-Induced Fluorescence

Report No. ARL-TR-2387
Authors: Sausa, Rosario C.; Swayambunathan, Vaidhianat; Singh, Gurbax
Date/Pages: February 2001; 39 pages
Abstract: Trace concentrations of energetic materials such as 2,4,6- trinitrotoluene (TNT), pentaerythritol tetranitrate (PETN),and hexahydro-l,3,5-tinnitro-s-triazine (RDX) are detected by laser photofragmentationlfragment detection (PF/FD) spectrometry. In this technique, a single laser operating near 227 nm photofragments the parent molecule and facilitates the detection of the characteristic NO fragment by means of its A2lr-X2 II (0,0) transitions near 227 nm. Fragment detection is accomplished by resonance-enhanced multiphoton ionization (REMPI) with miniature electrodes and by laser-induced fluorescence (LIF) with a photodetector. Experiments are also conducted in the visible region using 453.85-nm radiation for photofragmentation and fragment detection. Sand samples contaminated with PETN and RDX are analyzed by a pyrolysis/LIF technique, which involves pyrolysis of the energetic material with subsequent detection of the pyrolysis products NO and NO2 by LIF and PF/LlF, respectively, near 227 nm. Applying these techniques to the trace analysis of TNT, PETN, and RDX at ambient pressure in room air is demonstrated with limits of detection (S/N = 3) in the range of low parts-per-billion to parts-per-million for a 20-s integration time with l0-l20 micronj of laser energy at 226.8 nm and 5 mJ at 453.85 mm An increase in detection sensitivity is projected with an increase in laser energy and an improved system design. The analytical merits of these techniques are discussed and compared to other laser-based techniques.
Distribution: Approved for public release
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Last Update / Reviewed: February 1, 2001