MEASURING THE ELECTRONIC ABSORPTION SPECTRA OF GOLD NANOCLUSTERS VIA MASS SELECTIVE UV-VIS SPECTROSCOPY

Nanoscale engineering shows tremendous promise for developing new devices in energy transfer and storage, chemical synthesis, sensing, and a host of other applications. These applications critically depend on controlling electronic structure, but synthetic and experimental limitations hamper efforts to link electronic structure to dynamics and chemistry. We are overcoming these limitations by recording gas-phase, ultraviolet-visible (UV-Vis) spectra of ligand-protected gold nanoclusters with compositions precisely selected from a mixture by mass spectrometry. Clusters consisting of 6 to 9 gold atoms and varying ligand count and type were collected at 36 K and 4 K, with nitrogen and helium gas, respectively, physisorbing onto the surface of the clusters and acting as solvents. These spectra provide an unprecedented level of detail on the electronic structure of the clusters due to the homogeneous, contaminant-free environment and cryogenic temperatures in our instrument. With the aid of computational studies, experiments and analysis are underway to definitively assign the spectral features and to determine the factors that lead to shifts and splitting of transitions. The number and type of ligand and solvent species have a significant impact on transitions expected to involve only core metal atoms. Tracking the changes in the electronic transitions of gold nanoclusters with respect to chemical composition and structure will allow us to develop design rules to chemically manipulate their electronic structure, analogous to those developed for organic and organometallic molecular systems