On the fragmentation of benzene by multiphotoionization

The MPI fragmentation of benzene is analyzed on the basis of experimental data and the dissociation dynamics of C₆H₆⁺ at low excess energies. A multiple fragmentation mechanism with branchings is discussed in which vibrational energy is pumped into the C₆H ₆⁺ ground state by photon absorption and subsequent radiationless transitions. Calculations are performed for a statistical, products phase space model and show remarkably good agreement with the experimentally observed fragment patterns vs laser intensity. About 60 eV/molecule are required to make C⁺ the most abundant ion, if all the energy were initially present in the C₆H₆⁺. By RRKM estimates of the C₆H₆⁺ decomposition rate it is concluded that such an assumption is not realistic and a model with multiple absorption and fragmentation steps applies.