Application of superspace symmetry to optical and magnetic resonance spectra of incommensurably modulated crystals

The superspace description of incommensurable crystals is used to calculate the symmetry adapted crystal field potential for an incommensurable crystal. With this crystal field potential the perturbation of the high temperature phase energy levels by the incommensurable modulation can be calculated using perturbation theory. The results of such calculations on ThBr 4 are compared with the experimental results obtained from optical and magnetic resonance spectroscopy.