Interband effect in the optical response of strontium clusters

Photoabsorption spectroscopy has been performed on singly charged strontium clusters Sr-n(+) for the sizes n = 61, 127, and 200, in the 1.8 to 5.2 eV energy range. Superimposed on the giant resonance, related to the Mie plasm a resonance of a metallic sphere, the spectra reveal an extended wing in th e high-energy range attributed to interband transitions. Evidence of striki ng correspondence with the absorption spectrum of a macroscopic sphere obta ined from the measured real and imaginary parts of the bulk strontium diele ctric function is shown.