A COMPARISON OF FEMTOSECOND AND NANOSECOND MULTIPHOTON IONIZATION ANDDISSOCIATION FOR SOME NITRO-MOLECULES

Resonance-enhanced multiphoton ionization spectrometry (REMPI), using time-of-flight mass spectrometers and tuned lasers, has proved an impo rtant ultra-sensitive analytical technique, Nevertheless, conventional nanosecond REMPI suffers from a number of shortcomings: most importan tly, REMPI often fails through rapidly (pre)dissociating states, In th e case of thermally labile molecules, which include the nitro-molecule s, either no or very small parent or high/mass fragment ion peaks exis t, making the interpretation of the mass spectra ambiguous at best and often impossible, Femtosecond laser mass spectrometry (FLMS) can ofte n 'defeat' these dissociative states, resulting in large parent or hig h-mass fragment ion peaks which make the interpretation less ambiguous . In the present paper, nanosecond and femtosecond multiphoton ionizat ion and fragmentation are compared using time-of-flight mass spectrome try for NO2 gas and a number of different nitro-molecules: nitromethan e, nitrobenzene, m-nitrotoluene, dinitrotoluene and trinitrotoluene.