THE ROLE OF ELECTRON DELOCALIZATION IN THE IONIZATION OF C-6 HYDROCARBONS USING INTENSE 780 NM LASER-PULSES OF FEMTOSECOND DURATION

The photoionization/dissociation mass spectra are reported for the ser ies of molecules benzene (C6H6), 1,3,5-hexatriene (C6H8), cyclohexane (C6H12), and n-hexane (C6H14) as a function of laser power intensity f rom 1 to 3.8 x 10(13) W cm(-2) using a pulse duration of 170 fs and wa velength 780 nm. The ionization orders are localized around 8.3 for be nzene, 1,3,5-hexatriene, and cyclohexane and the relative ionization p robabilities are measured to be 1,79, and 0.15, respectively. No ion c urrent was observed for n-hexane. The dissociation yield is observed t o increase exponentially as a function of the number of atoms in the m olecule with cyclohexane undergoing the most dissociation and benzene undergoing essentially no dissociation. These observations are interpr eted in light of a field ionization model that incorporates both the i onization potential and the electronic and nuclear structure of the mo lecule. (C) 1998 American Institute of Physics.