Trace Detection of Nitrocompounds by ArF Laser Photofragmentation/Ionization Spectrometry

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A new method for detecting trace vapors of NO2-containing compounds near atmospheric conditions has been demonstrated with the use of one-color-laser photofragmentation/ionization spectrometry. An ArF laser is employed to both photolytically fragment the target molecules in a collision-free environment and ionize the characteristic NO fragments. The production of NO is hypothesized to result from a combination of two NO2 unimolecular fragmentation pathways, one yielding NO in its X 2Π electronic ground state and the other in its A 2Σ+ excited state. Ionization of ground-state NO molecules is accomplished by resonance-enhanced multiphoton ionization processes via its A 2Σ+X 2Π (3, 0), B 2Π ← X 2Π (7, 0) and/or D 2Σ+X 2Π (0, 1) bands at 193 nm. The analytical utility of this method is demonstrated in a molecular beam time-of-flight apparatus. Limits of detection range from the parts-per-million (ppm) to parts-per-billion (ppb) level for NO, NO2, CH3NO2, dimethylnitramine (DMNA), ortho- and meta-nitrotoluene, nitrobenzene, and trinitrotoluene (TNT). Under effusive beam experimental conditions, discrimination between structural isomers, ortho-nitrotoluene and meta-nitrotoluene, has been demonstrated with the use of their characteristic photofragmentation/ionization mass spectra.

Keywords: ArF excimer laser; NOx detection; Photofragmentation spectroscopy; Resonance-enhanced multiphoton ionization (REMPI)

Document Type: Research Article


Affiliations: 1: U.S. Army Research Laboratory, AMSRL-WT-PC, Aberdeen Proving Ground, Maryland 21005-5066; NRC/NAS Postdoctoral Research Associate 2: U.S. Army Research Laboratory, AMSRL-WT-PC, Aberdeen Proving Ground, Maryland 21005-5066

Publication date: November 1, 1993

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