A three-site, three-harmonic oscillator vibronic model Hamiltonian that includes correlation effects is considered in order to study the optical absorption spectra of the Creutz-Taube ion at various values for the total charge. The model is made by a two band Hubbard Hamiltonian, plus a vibronic interaction that is linear in the nuclear coordinates. We show that the main features of absorption spectra observed experimentally in the near-IR-visible are well reproduced by this model, as far as band position and shape are concerned. An approximate approach to the vibronic problem reveals that, in the present case, the vibronic interaction is strong and good results can be obtained only by solving the full vibronic problem.