The photofragmentation of the nitrotoluene isomers in the gas phase is studied in the wavelength region 210-270 nm using a pulsed UV laser in conjunction with a time-of-flight mass spectrometer. Laser-induced mass spectra are analysed and compared with those produced by the electron impact technique. The generation of the observed fragment ions is explained by invoking different fragmentation pathways followed by these molecules. Observed differences in the mass spectra of the ortho-meta-, and para-nitrotoluene isomers and in the wavelength dependence of the NO fragment released from these molecules are discussed as a possible way of providing a laser-based method for their identification.Recently, it has been shown by Kosmidis et al.' that the mass spectrum from the multiphoton ionization and dissociation of nitrobenzene, using UV laser light, can be explained by both the dissociation ionization (DIdissociation followed by ionization) and the ionization dissociation (ID-ionization followed by dissociation) decomposition mechanisms. For these two fragmentation routes, different dissociation pathways have been proposed.Due to the similarities which exist between nitrobenzene and the nitrotoluene isomers it is believed that many common characteristics could appear in their photodissociation processes. Thus, while the knowledge of the photochemistry of nitrobenzene is essential for understanding that of the nitrotoluene isomers, it is expected that the latter could contribute to the understanding of the entire group of nitro-explosive compounds which includes dinitrotoluene and trinitrotoluene. Moreover, this knowledge is a prerequisite for the sensitive and selective photodetection of these materials.The photodecomposition of the nitrobenzene molecule has been extensively studied using laser light, but the case is different for the nitrotoluenes. Although the fragmentation of their molecular ions has been well by other techniques, little work has been presented for molecular fragmentation using lasers.'"'' These laser studies do not, however, cover all the isomers and have mainly been carried out using a small number of discrete wavelengths.In this paper, the UV-laser-induced dissociation of ortho-, meta-and para-nitrotoluene in the gas phase is presented in the wavelength range 210-270 nm. The electron impact (EI) mass spectra of these molecules have also been recorded for reasons of completeness, and are compared with the laser-induced mass spectra.The study is carried out in this wavelength range for two reasons. Firstly, there is the possibility to study the molecular fragmentation with respect to the ionization thresholds. For aromatic molecules, it has been proposed that the extensive fragmentation observed after a

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A triple-quadrupole spectrometer has been used to study proton-transfer reactions of multiply charged ions generated by electrospray ionization. Doubly and triply charged ions generated from the peptides Arg-Lys-Glu-Val-Tyr and Met-Lys-bradykinin, respectively, were found to undergo proton-transfer reactions with ammonia molecules contained in the RF-only quadrupole collision-gas cell of the spectrometer. With horse-heart myoglobin in the source, ions having charges of 20+, 19+, 16+ and 14+ were selected in turn by the first quadrupole and their proton-transfer reactions with ammonia investigated. For each ion, numerous product ions were detected having charges (n-1)+, (n-2)+, (n-3)+ ... where n was the charge on the reacting parent ion. The possibility of using the experimental technique to measure approximately the proton affinities of multiply charged ions is discussed. Also, a procedure is outlined for identifying the charge states of product ions resulting from collision-induced dissociation of multiply charged ions.

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