The interaction of an excess electron with a polar molecular environment is well known as electron solvation.
This process is characterized by an energetic stabilization and by changes of the electronic spatial
extent due to screening of the localized charge through molecular rearrangement.
At metal-ice interfaces we photo-inject delocalized electrons from the metal substrate
into adsorbed ice layers and analyze the ultrafast dynamics of electron transfer,
localization and solvation by femtosecond time- and angle-resolved two-photon photoemission spectroscopy.
To acquire further understanding of the individual steps of the complex process we vary the interfacial structure.
The substrate is changed between Cu(111) and Ru(001) and the electron dynamics in ice islands
are compared to closed D2O layers. Contrasting crystalline and amorphous ice we found that electron solvation
is mediated through electron localization at favorable structural sites, which occurs very
efficiently in amorphous ice, but is less likely in a crystalline layer. Next, we find that in an open ice
structure like ice islands the energetic stabilization due to electron solvation proceeds
at a rate of 1 eV/ps which is three times faster than in a closed ice layer. We attribute this behavior to
differences in the molecular coordination, which determines the molecular mobility and, thus,
the transfer rate of electronic energy to solvent modes. The substrate's electronic structure, on the other
hand, is important to understand the transfer rates from electrons in ice back to the metal.
First experiments on trapped electrons in crystalline ice underline the potential to study electron
solvation not only during the equilibration process, but also in quasi-static conditions,
where we find that the stabilization continues, although at much weaker rates.
The publication is available at link doi:10.1016/j.progsurf.2005.06.001