Electron Transfer and Solvation Dynamics at Solid Cesium-Copper Interfaces in Presence of Solvents
The objective of this thesis is to decipher the fundamental mechanisms during the solvation of alkali in polar and nonpolar solvents on a metal surface. These mechanisms include electrostatic interaction between adsorbates, hydrogen bonding, van der Waals interactions and image charge interactions on the surface. The interplay of such fundamental interactions are decisive for the structure of the alkali-solvent adsorbates at interfaces. In addition, resonant excitation of the alkali results in a coupled alkali-solvent dynamics which in turn increases the lifetime of the excited alkali as well as induce energy transfer to the solvent molecules. This work addresses electronic structure and dynamics of the solvation of Cs+ in D2O and Xe on Cu(111) as a representative solvents with polar and nonpolar behaviour,
The surface science approaches have enabled the preparation of adsorbates on metal substrates with well-controlled coverages. In the solvation of Cs+ in D2O on Cu(111), the water-water interactions are preferred over water-Cs+ interactions and that result in a solvation pattern where ions reside at the periphery of the clusters. Such structures exhibit a hybrid alkali-water electronic state and its energy varies as a function of adsorbate coverage ratio. The excited state dynamics of this hybrid state depends on the coordination of the alkali to the solvent molecules.
In the solvation of Cs+ in Xe on Cu(111), it is observed that the energy of the Cs 6s state increases with Xe coverage and concomitantly the intensity of the photoemission decreases. This is attributed to the gradual decoupling of the bonding between Cs+ and Cu(111). In addition, the lifetime of the excited Cs 6s state has increased significantly upon adsorption of Xe. These properties of the Xe are attributed to the polarization of its charge density by Cs+ ions on the surface. Remarkably, no hybrid alkali-Xe state on Cu(111) is observed during the interaction. This suggests a sharp contrast in the solvation of Cs+ ions in the polar and the nonpolar solvents.
This work reveals the dominant nature of the cooperative interactions during the solvation of alkali in polar solvents whereas alkali solvation in nonpolar solvent exhibits a competitive nature of the Coulomb and van der Waals interactions on the surface.