  We report resonant inelastic x-ray scattering studies of electronic
excitations in a wide variety of cuprate compounds. Specifically, we focus on
the charge-transfer type excitation of an electron from a bonding molecular
orbital to an antibonding molecular orbital in a copper oxygen plaquette. Both
the excitation energy and the amount of dispersion are found to increase
significantly as the copper oxygen bond-length is reduced. We also find that
the estimated bond-length dependence of the hopping integral t_pd is much
stronger than that expected from tight-binding theory.
