  We study orbital excitations in the optical absorption spectra of YVO3 and
HoVO3. We focus on an orbital absorption band observed at 0.4 eV for
polarization E parallel c. This feature is only observed in the intermediate,
monoclinic phase. By comparison with the local crystal-field excitations in
VOCl and with recent theoretical predictions for the crystal-field levels we
show that this absorption band cannot be interpreted in terms of a local
crystal-field excitation. We discuss a microscopic model which attributes this
absorption band to the exchange of two orbitals on adjacent sites, i.e., to the
direct excitation of two orbitons. This model is strongly supported by the
observed dependence on polarization and temperature. Moreover, the calculated
spectral weight is in good agreement with the experimental result.
