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.