Time-resolved studies of chemical reactions in clusters

Abstract

Excited-state proton transfer (ESPT) rates in molecular clusters were measured as a function of cluster size using picosecond spectroscopy in a molecular beam mass spectrometer. ESPT from the S1 state of phenol to basic solvent clusters (NH3)n occurs for a critical solvent cluster size n ≥5 with a rate constant of k= (60 ± 10 ps)-1 for n = 5−7. ESPT showing critical cluster-size dependencies was also observed in the basic solvent N(CH3)3 (n ≃ 3). Proton transfer was not observed in the less basic solvent clusters (CH3OH) n and (H2O) n . Mixed solvent studies indicate that the addition of a dissimilar molecule to an otherwise neat solvent cluster impedes ESPT presumably due to a disruption of the hydrogen bonding network.