Mechanism and power dependence of the multiphoton ionization of bromobenzene

The multiphoton ionization and fragmentation of bromobenzene is examined in the low and medium power regimes. Single-photon excitation to the 1B2 state is followed by a one-photon absorption that leads to the parent ion. Subsequent absorptions lead to the C6H+5 and C4H+x species. Mass-resolved studies of this resonance-enhanced two-photon process are in qualitative agreement with a kinetic model. The power dependencies of the parent, phenyl, and C4H+x ions are successfully predicted and simple relationships for the branching ratios are evident. Information on the relative cross sections for photon absorption by the ions is obtained. The analysis of the data suggests that the primary route is ionization to form the parent with subsequent formation of the fragments occurring via a ladder-switching mechanism.