FORMATION OF PROTONATED AMMONIA CLUSTERS PROBED BY A FEMTOSECOND LASER

Femtosecond pump-probe techniques combined with a reflectron time-of-f light mass spectrometer are employed to investigate the formation mech anisms of protonated ammonia clusters. Pump pulses are employed to exc ite the ammonia clusters to electronically excited states correspondin g to selected A or C' states, while probe pulses with variable delay t imes are used to ionize the clusters. The results reveal that both the absorption-ionization-dissociation and absorption-dissociation-ioniza tion mechanisms occur in the A state, while the absorption-ionization- dissociation mechanism is the sole one operative in the C' state.