Visible and UV multiphoton ionization and fragmentation of polyatomic molecules

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Abstract
It is now known that tunable dye laser light leads to resonance enhanced photoionization of molecules in a mass spectrometer via multiphoton absorption. In some cases this process also leads to ion fragmentation. Time delayed tandem laser pulses of different wavelengths are employed to study the mechanism of this multiphoton ionization and fragmentation process in benzene. The experimental results strongly indicate that excitation does not proceed up an autoionization ladder of the neutral molecule, rather the multiphoton process is shown to be due to the climbing of two independent ladders, one up to the ionization potential in the neutral molecule, the second in the new species of molecular parent ions produced. Hence multiphoton ionization could also form a new basis of ion spectroscopy.