In the photon-energy region 1.5-6.5 eV, a size-dependent change in interband transitions associated with the d bands of metal particles has been detected directly for the first time by measuring the transmittance spectrum and its derivative of Cu island films. It is shown that the narrowed d bands for Cu particles smaller than 70Å in diameter depart from flatness gradually from the highest to the lowest levels with decreasing particle size. Comparing the d bands of bulk Au surface, this d-band change is shown to be connected with the reduced coordination number of atoms on the particle surface.
