AbstractThe classical dispersion equation for the extraordinary IR spectrum of uniaxial crystals is shown to be valid, even if damping is included. The directional dependence of the damping factors γj(ϑ) and their effect on the other oscillator parameters (dispersion frequencies ωj(ϑ), oscillator strengths 4 πσj(ϑ) is investigated in detail. Evidence is given for the validity of a sum rule of damping factors. The theory is applied to MgF2, ZnF2and α