Infrared electron modes in light deformed clusters

Infrared quadrupole modes (IRQM) of the valence electrons in light deformed sodium clusters are studied by means of the time-dependent local-density approximation. IRQM are classified by angular momentum components λμ=20, 21, and 22 whose μ branches are separated by cluster deformation. In light clusters with a low spectral density, IRQM are unambiguously related to specific electron-hole excitations, thus giving access to the single-electron spectrum near the Fermi surface. Most of the IRQM are determined by cluster deformation and so can serve as a sensitive probe of the deformation effects in the mean field. The IRQM branch λμ=21 is coupled with the magnetic scissors mode, which enables us to detect the latter. We discuss two-photon processes, Raman scattering, stimulated emission pumping, and stimulated adiabatic Raman passage as the relevant tools to observe IRQM. An alternative method to detect the IRQM population in clusters is proposed.