Femtosecond dynamics of benzene(NH3)n complexes in highly excited states

The dynamic off benzene(NH3)n heteroclusters is studied with 170 fs laser pulses in a molecular beam. The clusters were excited to about 6.2 eV, i.e. above the S2 state of bare benzene. By varying the probe energy (3.1 and 4.65 eV) we examined the dynamics of internal conversion and their dependence on the cluster size. The obtained time constants of internal conversion are in the order of 100 fs. The ultrafast dynamics were not observed before and show that earlier nanosecond studies were only revealing the long-time behaviour after further relaxation and fragmentation of the vibrationally highly excited complexes.