  We observe the low-lying excitations of a molecular dimer formed by two
electrons in a GaAs semiconductor quantum dot in which the number of confined
electrons is tuned by optical illumination. By employing inelastic light
scattering we identify the inter-shell excitations in the one-electron regime
and the distinct spin and charge modes in the interacting few-body
configuration. In the case of two electrons a comparison with
configuration-interaction calculations allows us to link the observed
excitations with the breathing mode of the molecular dimer and to determine the
singlet-triplet energy splitting.
