SUBPICOSECOND IONIZATION AND DISSOCIATION OF BENZENE AND CYCLIC ALKANES AT 800 AND 400 NM

The photoionization and dissociation processes induced by 200 fs laser pulses of 800 and 400 nm in benzene and the cyclic alkanes cyclopropa ne and cyclohexane have been studied by time-of-flight mass spectromet ry. At 800 nm and intensities up to 2.1 x 10(13) W cm(-2) benzene and cyclopropane parent ions are dominant in the mass spectra whereas cycl ohexane appears completely fragmented. At 400 nm and intensities up to 4.4 x 10(12) W cm(-2) a more extensive fragmentation is observed for all three molecules. The molecular ionization is attributed to a reson ant multiphoton process and the observed fragmentation to a predominan t ID (ionization followed by dissociation) ladder climbing mechanism. (C) 1998 published by Elsevier Science B.V. All rights reserved.