The energy levels for excitons in ${\mathrm{Cu}}_2$O under uniaxial stress have been calculated under the assumption of strong mixing between the yellow and green exciton series. The reversal of the order for the strain-split levels of the $2S$ yellow exciton with respect to the $1S$ yellow exciton is explained by two different and competing splitting mechanisms. The results agree well with resonance-enhancement measurements of Waters et al. The level assignment as proposed by Agekyan and Stepanov and Fröhlich et al. is confirmed.

• Received 10 March 1980

DOI:https://doi.org/10.1103/PhysRevB.23.597