  Absorption spectra of closed-shell Na_2, Na_3+, Na_4, Na_5+, Na_6, Na_7+, and
Na_8 clusters are calculated using a recently implemented conserving linear
response method. In the framework of a quasiparticle approach, we determine
electron-hole correlations in the presence of an external field. The calculated
results are in excellent agreement with experimental spectra, and some possible
cluster geometries that occur in experiments are analyzed. The position and the
broadening of the resonances in the spectra arise from a consistent treatment
of the scattering and dephasing contributions in the linear response
calculation. Comparison between the experimental and the theoretical results
yields information about the cluster geometry, which is not accessible
experimentally.
