ULTRAFAST NONRESONANT MULTIPHOTON PREPARATION OF ION-MOLECULE REACTIONS WITHIN CLUSTERS

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