CALCULATION OF THE FH2(OH-)-CENTER ABSORPTION-BANDS IN CSCL

The F(H2)(OH-)-center electron-energy levels in CsCl are calculated with use of a pseudopotential formalism in which the model Potential incorporates the point-ion potential, ion-size effects, and the interaction with both the OH- permanent and displacement dipole moments. Electronic polarization and a radial A1g, distortion of the nearest-neighbor cations are treated as perturbations. The F(H2)(OH-)-center model is an F center between two NNN OH- ions along <001> with the permanent dipoles pointing toward the vacancy, and the configuration has D4h point-group symmetry. The OH-displacement from the lattice site along <001> is taken as a model parameter, and it is adjusted to obtain agreement with the absorption bands. The model yields an average F(H2)(2)-band peak at 2.25 eV, compared with the observed value of 2.33 eV, and an F(H2)(1)-band peak at 1.38 eV, compared with the observed value of 1.31 eV. The optimum OH- displacement is 0.43 angstrom toward the vacancy accompanied by an 8% outward A1g, radial displacement of the NN Cs+ ions. The calculated A1g, localized-mode frequency is 2.42 X 10(12) Hz. The calculated ratio of the band oscillator strengths is 4.2, which is in good agreement with the experimental value of 3.2.