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Spectrometric Studies of Selected Nitrocompounds Using Laser-Induced Photofragmentation/Photoionization at 193 nm.
Final rept. Aug 93-Feb 94,
ARMY RESEARCH LAB ABERDEEN PROVING GROUND MD
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A new method for detection trace vapors of NO2 containing compounds near atmospheric conditions has been demonstrated using one color laser photofragmentationfragment 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 X2Pi electronic ground state and the other in its A2Sigma excited state. Ionization of ground state NO molecules is accomplished by resonance-enhanced multiphoton ionization processes via their A2Sigma -X2Pi 3,0, B2Pi -X2Pi 7,0, andor D2Sigma - X2Pi 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 photofragmentationphotoionization mass spectra. jg
APPROVED FOR PUBLIC RELEASE