Acetone And Methyl Ethyl Ketone, Multi-photon Ionization Mass Spectrometry

Resonance enhanced multi-photon ionization (REMPI) technique develops and improves following the appearance and development of laser. Cooperating with time of fly spectroscopy, it can achieve dual selections (mass spectrum selection and spectroscopy selection) during the ionization and detection process. Compared with the other methods, the technique has much advancement: high sensitivity, elaborate selectivity, high resolution etc. Ever since then the method has been playing an important role in environment pollutant detection, material composition analysis and so on. Meanwhile it has intersected with many fields and has got many returns.Ketenes have abundant physical and chemical characters, and many researchers take interest in it both home and abroad. So ketenes have been long the research center of optical-physics and optical-chemistry; especially acetone, with small mass number and perfect symmetry, quite a lot of studies have been done on it. If one methyl of Acetone is substituted by an ethyl, an acetone molecule changes into a 2-butanone molecule, CH₃COC₂H₅. The research for 2-butanone can help to understand the influences of structure and symmetry on characters.We adopt laser spectroscopy; and take 355nm and 532nm as excitation lamp pulse. We have studied the multi-photon ionization time of flight mass spectrum (MPI-TOFMS) of acetone, 2-butanone and xyiene. The main signals are C⁺,CH⁺,CH₂⁺,C₂⁺,C₂H₂⁺ and so on. CHO⁺ (m/e=29) in acetone spectrum and C₂H₃O⁺ (m/e=43) in 2-butanone spectrum origin from their isomers.The mass spectrums at 532nm are quite abundant compared with spectrums at 355nm; there are ions with m/e=4,6, 8 at 532nm. In our opinion they are ought to be multiply charged ions, but there is no relative report about multiply charged ion under similar condition, so advanced research is needed for the appearance of this phenomenon and the affirmation of these ions. No argument is made here about them. The mass spectrums of acetone and 2-butanone are much simpler. No acetone or 2-butanone molecule ions are detected during experiments.The ionization and dissociation mechanism is discussed. According to Getanken's theory acetone belongs to mechanism C, while 2-butanone belongs to mechanism B. No acetone or 2-butanone molecule ions are detected.The main ions in xylene MPI-TOF mass spectrum are mainly the ions with m/e equal to 1,12,24; no xylene molecule ion is found.