Ionization and fragmentation dynamics of benzene in intense laser fields by tandem mass spectroscopy

Using a tandem time-of-flight mass spectrometer, benzene cations produced b y the resonantly enhanced multiphoton ionization are mass separated and are exposed to intense laser fields (similar to 2x10(16) W/cm(2)) at lambda si milar to 790 and 395 nm with the pulse duration of similar to 50 fs. Compar ing the yields of the product ions with those obtained from neutral benzene molecules, the ionization and dissociation dynamics of benzene in intense laser fields is investigated. At lambda similar to 790 nm, the formation of parent benzene ions is a dominant process irrespective of the initial char ge states, i.e., major products obtained when starting from neutral benzene are benzene cations and dications and those obtained when starting from be nzene cation are benzene dications. On the other hand, at lambda similar to 395 nm, the fragmentation processes to produce C4Hi+(i=2-4) and C3Hj+(j=1- 3) dominate over further ionization to the benzene dication for both cases starting from neutral benzene and benzene cation, indicating the population trapping occurs by the efficient confinement in the light-dressed mixture of the C and X states of benzene cations assisted by the ultrafast intramol ecular decay process. (C) 2001 American Institute of Physics.