PROTON-TRANSFER DYNAMICS AND CLUSTER ION FRAGMENTATION IN PHENOL AMMONIA CLUSTERS

Excited-state proton transfer dynamics are reported for the phenol(NH3 )n cluster system. Excited-state proton transfer is shown to occur for this system by isotopic substitution of the hydroxyl proton and ammon ia protons. The observed dynamics slow from 80 to 600 ps upon cluster deuteration. The effects of cluster vibrational energy and ammonia con centration in the expansion gas are also studied. The results of these experiments are compared with a previous study [Syage and Steadman, J . Chem. Phys. 95, 2497 (1991)] which used a single excitation energy a nd varied ionization energy. Our experiments indicate that a significa nt amount of cluster ion fragmentation occurs for this system and caut ion must be exercised in assigning the decays observed in a given ion mass channel to a particular parent cluster. Due to the difficulties o f associating a given decay curve with a cluster of particular mass, a previously proposed model of proton transfer in isolated clusters [Hi neman et al., J. Chem. Phys. 97, 3341 (1992)] which details the effect of cluster vibrational energy on the proton transfer rate cannot be a pplied to the phenol/ammonia system.