  The dispersion of the in-plane Cu-O bond-stretching LO phonon mode in the
high-$T_{C}$ superconducting cuprates shows strong softening with doping near
the zone boundary. We suggest that it can be described with a negative
electronic dielectric function that results in overscreening of inter-site
Coulomb interaction due to phonon-induced charge transfer and vibronic
electron-phonon resonance. We propose that such a strong electron-phonon
coupling of specific modes can form a basis for the phonon mechanism of
high-temperature superconductivity. With the Eliashberg theory using the
experimentally determined electron dispersion and dielectric function, we
demonstrate the possibility of superconductivity with the order parameter of
the $d_{k_{x}^{2}-k_{y}^{2}}$ symmetry and the transition temperature well in
excess of 100K.
