Within the framework of the time-dependent local-density approximation and the self-interaction correction, we have estimated the photoionization cross-section and the photoelectron angular asymmetry parameter of C 60 . The latter exhibits large variation around the surface plasmon resonance of the π electrons near 20 eV. Based on a semiclassical electrodynamics model, we show that this behaviour is generic for any surface plasmon resonance in the continuum and is a signature of the correlated motion of the electrons. It is related to the change of sign of the real part of the dynamical polarizability at resonance. Possible experiments to investigate this new plasmon signature are discussed.

We study the spin-dependent electronic excitations in alkali-metal nanoparticles. Using numerical and analytical approaches, we focus on the resonances in the response to spin-dependent dipole fields. In the spin-dipole absorption spectrum for closed-shell systems, we investigate in detail the lowest-energy excitation, the "surface paramagnon" predicted by L. Serra et al. [Phys. Rev. A 47, R1601 (1993)]. We estimate its frequency from simple assumptions for the dynamical magnetization density. In addition, we numerically determine the dynamical magnetization density for all low-energy spin-dipole modes in the spectrum. Those many-body excitations can be traced back to particle-hole excitations of the noninteracting system. Thus, we argue that the spin-dipole modes are not of collective nature. In open-shell systems, the spin-dipole response to an electrical dipole field is found to increase proportionally with the ground-state spin polarization.Comment: 12 pages, 9 figure

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