Photoionization, fragmentation and proton transfer in 1-naphthol(NH3)n clusters

The fragmentation of photoionized 1-naphthol·(NH3)n clusters is examined. In one-color resonant two-photon ionization experiments, fragmentation in the ion state is observed for every cluster size above n=1. For small clusters (n≤4), a single neutral ammonia is evaporated in the ion state. This ceases at energies 1500–2500 cm−1 above the ionization thresholds. Larger clusters, n≥5, are readily ionized at much lower energies than n≤4. They yield (1-naphthol·(NH3)n)+, 1-naphthol·(NH3)nH+, and (NH3)nH+ ion fragments. Several neutral ammonia molecules can be lost. These observations support predictions that n≥5 clusters undergo proton transfer in the ground state.