Laser photofragmentation-fragment detection and pyrolysis-laser-induced fluorescence studies on energetic materials

Trace concentrations of energetic materials such as 2,4,6-trinitrotoluene ( TNT), pentaerythritol tetranitrate (PETN), and hexahydro-1,3,5-trinitro-s-t riazine (RDX) are detected by laser photofragmentation-fragment detection ( PF-FD) spectrometry. In this technique, a single laser operating near 227 n m photofragments the parent molecule and facilitates the detection of the c haracteristic NO fragment by means of its A (2)Sigma(+)-X (2)Pi (0, 0) tran sitions near 227 nm. Fragment detection. is accomplished by resonance-enhan ced multiphoton ionization with miniature electrodes and by laser-induced f luorescence (LIF) with a photodetector. Experiments are also conducted in t he visible region by use of 453.85-nm radiation for photofragmentation and fragment detection. Sand samples contaminated with PETN and RDX are analyze d by a pyrolysis-LIF technique, which involves pyrolysis of the energetic m aterial with subsequent detection of the pyrolysis products NO and NO2 by L IF and PF-LIF, respectively, near 227 nm. The application of these techniqu es to the trace analysis of TNT, PETN, and RDX at ambient pressure in room air is demonstrated with limits of detection (signal-to-noise ratio, 3) in the low parts-in-10(9) to parts-in-10(6) range for a 20-s integration time and 10-120 mu J of laser energy at 226.8 nm and similar to 5 mJ at 453.85 n m. An increase in detection sensitivity is projected with an increase in la ser energy and an improved system design. The analytical merits of these te chniques are discussed and compared with those of other laser-based techniq ues. (C) 1999 Optical Society of America.