We investigate the effect of site-selective isotope substitution on the Ram
an spectra of the yttrium-barium cuprate by means of first-principles bands
tructure calculations. Upon oxygen isotope substitution we find a dramatic
change in the Raman scattering intensities which is much more pronounced th
an the shift of the phonon frequencies. This effect is due to large changes
in the eigenvectors caused by the site-selective substitution.