Optical absorption in small metal particles

The optical absorption of small metal particles is investigated using the hard-walled sphere model of noninteracting electrons in an infinitely deep spherical potential well. An analytical formula is obtained for the frequency-dependent dielectric function, valid if the particle radius greatly exceeds the inter-electron spacing. The exact result lies between the earlier approximations of Kawabata and Kubo and of Hache et al. for the same model. As the radius gets smaller, the absorption shows pronounced oscillations, attributable to shell effects, as a function of frequency.