Nonadiabatic approach to tunneling centers and their isotope effect

Abstract

In previous theoretical work on paraelectric centers (e.g., KCl: O${\mathrm{H}}^{-}$) the inertia of the tunneling particle (e.g., ${\mathrm{H}}^{+}$) has been neglected (adiabatic approximation). In the present work a nonadiabatic treatment of the phonon-assisted tunneling is given. A considerable alteration in the transition rates is found. Further on, the isotope effect is shown to exhibit "dynamical" features in addition to the "static" ones treated so far. A 90° transition for KCl: O${\mathrm{H}}^{-}$ is calculated. Idealized lattice dynamics is used in the form of the Debye model.