PHOTOIONIZATION DISSOCIATION OF ALKYL SUBSTITUTED BENZENE MOLECULES USING INTENSE NEAR-INFRARED RADIATION/

The photoionization products for benzene, toluene, ethylbenzene and n- propylbenzene are measured using time-of-flight methods upon interacti on with 780 nm radiation pulses of duration 170 fs and intensity 10(13 -13.6) W cm(-2). The relative ionization yields scale as 1, 1.2, 1.4, and 0.35 for benzene, toluene, ethylbenzene and n-propylbenzene at max imum laser intensity. Limited dissociation was observed for benzene an d toluene at all laser power densities. A significant (> 5%) dissociat ion/ionization yield was observed for ethylbenzene and n-propylbenzene at the lowest laser power densities. The dissociation increased as 11 th order and 9th order processes for ethylbenzene and n-propylbenzene, respectively to a maximum of 70% dissociation/ionization for n-propyl benzene at 3.8 X 10(13) W cm(-2). At 3.8 X 10(13) W cm(-2) the dissoci ation yield increases quadratically with alkyl chain length for the se ries. The observed ionization/dissociation trends are consistent with a model which incorporates both Field ionization and energy redistribu tion concepts.