Short pulse laser mass spectrometry of nitrotoluenes: ionization and fragmentation behavior

The mass spectra of all isomers of mononitrotoluene, four isomers of dinitrotoluene and of 2,4,6,-trinitrotoluene, obtained by multiphoton ionization utilizing ultrashort laser pulses with center wavelengths of either 206 nm or 412 nm, are presented and discussed. Under these ionization conditions all nitrotoluenes exhibit a high degree of fragmentation which increases with the degree of substitution. For the compounds having a nitro group in position 2 and/or 6 a pronounced ortho effect leading to the loss of OH is observed. The fragmentation patterns in the lower mass range are typical for alkylated aromatic substances. While no fundamental differences between the mass spectra obtained with the two wavelengths were observed, the visible light in all cases resulted in a broader variety of fragments and additional signals in the higher mass range. The latter can be used for isomer identification.