Dynamics of Charge-Transfer-to-Solvent Precursor States in I-(water)n (n) 3-10) Clusters Studied with Photoelectron Imaging†

The dynamics of charge-transfer-to-solvent states are studied in I-(H2O)n)3-10 clusters and their deuterated counterparts using time-resolved photoelectron imaging. The photoelectron spectra for clusters with n g 5 reveal multiple time scales for dynamics after their electronic excitation. An increase in the vertical detachment energy (VDE) by several hundred millielectronvolts on a time scale of 1 ps is attributed to stabilization of the excess electron, primarily through rearrangement of the solvent molecules, but a contribution to this stabilization from motion of the I atom cannot be ruled out. The VDE drops by 50 meV on a time scale of tens of picoseconds; this is attributed to loss of the neutral iodine atom. Finally, the pump-probe signal decays with a time constant of 60 ps-3 ns, increasing with cluster size. This decay is commensurate with the growth of very slow electrons and is attributed to autodetachment. Smaller clusters (n) 3, 4) display simpler dynamics. Anisotropy parameters are reported for clusters n) 4-9. 1