Ultrafast non-resonant multiphoton preparation of ion-molecule reactions within clusters

Using two-photon non-resonant excitation with a picosecond tunable laser, ion-molecule reactions have been initiated in the ground state of ionic clusters. Two examples are treated here of nucleophilic attack of ammonia on para-fluorochlorobenzene and meta-chloroiodobenzene cations. The reaction products are easily observed and identified in the first state without further fragmentation. The second system has been chosen for its lack of a stable relay state for the resonant ionisation. These experiments demonstrate the potential of pico (femto) tunable light sources in preparing reactions of ionic states by two-photon (or three-photon) non-resonant excitation. This method should be rather general even in the absence of a stable intermediate state.