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 resonant two-color two-photon ionization of the neutral cluster. If the second 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 fragmentation rate on the excess energy can be deduced. These experimental rates are compared to microcanonical decay constants k(E) calculated from Rice–Ramsperger–Kassel–Marcus (RRKM) theory based on ab initio data solely. Received: 8 March 2000 / Revised version: 28 April 2000 / Published online: 5 October 2000