REMPI TIME-OF-FLIGHT MASS-SPECTRA OF C2H7N ISOMERS

Using a time of flight (TOF) mass spectrometer, we obtained the multip hoton ionization (MPI) spectra of ethylamine (EA) and dimethylamine (D MA) molecules in the region of 440 nm-470 nm with a dye laser and at 5 32 nm with a Nd:YAG laser respectively. Both kinds of molecular ions a re formed through resonance enhanced multiphoton ionization (REMPI) vi a Rydberg states. The fragment ions come from the dissociation of the corresponding molecular ion. The MPI-MS patterns of the two isomers ar e readily distinguished. The beta-cleavage of the EA molecular ion is dominant. The currents of the molecular ion and the ion created by its pseudo-beta cleavage are strongest in the MPI-MS of the DMA molecule. Softer ionization occurs at longer wavelengths as the initially forme d molecular ions have less excess energy. The reactions of CH4N+ ions from different precursors are also structure related: they fragment mo re extensively in MPI of DMA molecules than in that of EA molecules. ( C) 1998 Elsevier Science B.V. All rights reserved.