97-08U

The Electron spectrum KDP-type crystals has been invistigated as a function of external hydrostatic pressure using the tigh-binding approximation. The joint density of electron states, real and imaginary parts of the dielectric permeability, refraction index, gyration coefficients, absorption and reflection coefficients for different polarization of light are determined. There pressure and frequency dependiences are investigated. The results are discussed by comparing with experimental data on piezooptic coefficients. The anomalous behaviour of the optical constants at the pressure $p \simeq 17$ kbar are due to the transformation of the hydrogen bond from two minimum to one minimum bond, when the proton to be located at the midpoint of the hydrogen bond