Structure-reactivity effects in the picosecond dynamics of isolated clusters

Abstract

The link between gas-phase and condensed-phase chemical dynamics is being sought by the study of reactivity in small molecular clusters. We present measurements of reaction rates as a function of cluster size and composition to elucidate the role of solvent on a single-molecule basis. In previous work we showed that reactivity in clusters is strongly correlated to the stepwise binding energies of individual solvent molecules. Here, we show that solvent structure also plays a large role in determining chemical reactivity. This paper focuses on the excited state proton transfer reaction of phenol (PhOH) in a cluster of solvent-like molecules (i.e., NH3 and CH3OH). Three cases of structure-reactivity effects are reported: (1) rate inhibition by the addition of a CH3OH molecule to an (NH3) solvent cluster (60 ps vs 500 ps), (2) very different reaction rates for the inequivalent phenol molecules in phenol dimer solvated by (NH3) (50 ps vs 500 ps), and (3) solvent reorganization following proton transfer that occurs on the time scale of 0.3 ns.