| Photoelectron spectroscopy has developed into one of the most versatile and successful tools for probing molecular and cluster anions. Recently, this technique has been combined with an ultrafast laser system for a direct time-domain investigation of cluster dynamics. Using this technique, we report for the first time the localization and photodetachment of the excess electron in the excited state of hydrated electron clusters, (H2O) n-. Furthermore, by photoexciting these clusters near the detachment threshold, a "simulation" of the electron attachment process could be obtained, and subsequently, its lifetime can be determined. Utilizing pump-probe femtosecond photoelectron spectroscopy, a qualitative excited state lifetime of the anionic water clusters has been measured by accessing the excited state with the first ultrafast pulse, then variably delaying the detaching photon.; A more direct observation of the electron attachment process in these negatively charged clusters was made using traditional (direct detachment) photoelectron spectroscopy. Specifically, in hydrated electron clusters, (H 2O)n-, we attempt to clarify previous results by exploring the nature of the trace species surrounding the intense parents appearing at magic numbers n = 2, 6, 7, and 11. We report photoelectron spectra for the small anionic water clusters, (H2O)n - (n = 2--11, excluding the tetramer). Using this technique, two isomeric forms for most of these small water anions, which are distinguishable by their vertical electron detachment energies (VDEs), have been observed. The feature corresponding to the more strongly bound form evolves continuously to the band characteristic of the larger (n ≥ 11) clusters, while the smaller clusters display a dramatically smaller sequential solvation shift. This disparity results in a sharp break in the cluster radius (∝n1/3) dependence of the VDEs, disputing earlier studies. |
