Unimolecular decay of hydrogen-bonded cluster ions

The unimolecular decay of the hydrogen-bonded phenol(H2O)(4)(+) cluster ion was studied both experimentally and theoretically. The ion is formed by re sonant two-color two-photon ionization of the neutral cluster. If the secon d color exceeds the dissociation threshold of the ion, fragmentation occurs on a microsecond time scale. By analyzing the time-of-flight (TOF) signal of the metastable ions at different excess energies the dependence of the f ragmentation rate on the excess energy can be deduced. These experimental r ates are compared to microcanonical decay constants k(E) calculated from Ri ce-Ramsperger-Kassel-Marcus (RRKM) theory based on ab initio data solely.