LASER IONIZATION STUDIES OF NITROAROMATIC AND NOX(X = 1 OR 2) MOLECULES IN THE REGION 224-NM-238-NM

Wavelength dependent ionisation studies have been carried out on the nitroaromatic molecules nitrobenzene and o-nitrotoluene as well as NO and NO2 gases in the wavelength region 224-238 nm. Mass spectra from the nitroaromatic molecules show extensive fragmentation with a particularly prominent NO+ ion peak. This particular fragment ion has been of great importance, not only as a marker to identify the presence of a nitro-type compound, but also to distinguish from NO(x)(x = 1 or 2) molecules from which it may have originated and to provide information about possible energy pathways in the fragmentation processes. The particular studies described in this paper were carried out to identify wavelength regions where greater ionisation efficiency of the NO molecule arising from the nitroaromatic molecules could be achieved. In the course of these studies an important difference in the NO+ wavelength dependent ionisation spectra of nitrobenzene and o-nitrotoluene was observed. The observation of atomic oxygen resonances in the nitrobenzene and NO2 Spectra suggest that similar pathways are being followed in these two dissociating molecules.