Time-Resolved Dynamics in Iodide-Uracil-Water Clusters upon Excitation of the Nucleobase

The dynamics of iodide-uracil-water (I·U·H2O) clusters following π-π* excitation of the nucleobase are probed using time-resolved photoelectron spectroscopy (TRPES). Photoexcitation of this cluster at 4.77 eV results in electron transfer from the iodide moiety to the uracil, creating a valence-bound (VB) anion within the cross-correlation of the pump and probe laser pulses. This species can decay by a number of channels, including autodetachment and dissociation to I or larger anion fragments. Comparison of the energetics of the photoexcited cluster and its decay dynamics with those of the bare iodide-uracil (I·U) complex provide a sensitive probe of the effects of microhydration on these species. The results are also compared with TRPES experiments on I·U·H2O at lower pump photon energies, where both the initial photoinduced dynamics and the decay of the photoexcited cluster are qualitatively different.