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Electronic excitations in atomic clusters: beyond dipole plasmon

Multipole electron modes beyond the Mie plasmon in atomic clusters are investigated within the time-dependent local density approximation theory (TDLDA). We consider the origin of the modes, their connection with basic cluster properties and possible routes of experimental observation. Particular attention is paid to infrared magnetic orbital modes, scissors and twist, and electric quadrupole mode. The scissors and twist modes determine orbital magnetism of clusters while the electric quadrupole mode provides direct access to the single electron spectra of the cluster. We examine two-photon processes (Raman scattering, stimulated emission pumping and stimulated adiabatic Raman passage) as the most promising tools for experimental investigation of the modes.