Calculation of theFH(OH−)-center absorption bands in CsCl

The $F_H$(${\mathrm{OH}}^{\mathrm{-}}$)-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, the interaction with the ${\mathrm{OH}}^{\mathrm{-}}$ finite-size permanent electric dipole moment, and the interaction with the electric dipole moment produced by displacement of the ${\mathrm{OH}}^{\mathrm{-}}$ ion from the lattice site. Electronic polarization and a radial $A_1$ distortion of the nearest-neighbor cations are treated as perturbations. The presence of the ${\mathrm{OH}}^{\mathrm{-}}$ ion in the next-nearest-neighbor position to the vacancy reduces the point-group symmetry to $C_{4v}$. The orientation of the ${\mathrm{OH}}^{\mathrm{-}}$ permanent dipole moment and the ${\mathrm{OH}}^{\mathrm{-}}$ displacement from the lattice site, both along 〈001〉, were used as model parameters and were adjusted to obtain agreement with the observed peaks of the $F_H$(1) and $F_H$(2) bands. The model yields a calculated $F_H$(1) band peak of 1.62 eV compared with the observed value of 1.57 eV, and a calculated $F_H$(2) band peak of 2.28 eV compared with the observed value of 2.31 eV. The ${\mathrm{OH}}^{\mathrm{-}}$ ion is oriented with the positive end closest to the vacancy; the center of the mass is displaced 0.15 Å toward the vacancy; and the radial A1 distortion of the nearest neighbors is outward 8% of the internuclear separation. There is considerable dipolar mixing of the ‖S〉 and ‖Z〉 basis states where the ${\Vert }^1$ $A_1$〉 ground state is given by 0.796‖S〉+0.605‖Z〉. .AE