On the Electronic Structures of Au25(SR)18 Clusters Studied by Magnetic Circular Dichroism Spectroscopy

The first magnetic circular dichroism (MCD) spectra are reported at room temperature for well-defined thiolate-protected Au25 clusters (Au25(SG)18 and Au25(PET)18, where SG and PET denote glutathione and 2-phenylethanethiolate, respectively). MCD essentially corresponds to electronic transitions in the absorption spectrum, so the electronic structures of the Au25 clusters are explored based on a simultaneous deconvolution analysis of both the electronic absorption and MCD spectra, giving enhanced spectral resolution. We then find that the observed MCD responses are entirely interpreted in terms of the Faraday B terms, representing strict nondegeneracies of the excited and ground states of the Au25 clusters that correspond to so-called superatom D and P orbitals, respectively.