Magnetic- and Electric-Field Effects of theB1andB2Absorption Lines in Ruby

A pseudo-Stark splitting of the $B_1\left(20\mathrm{}993 {\mathrm{cm}}^{-1\mathrm{}}\right)$ and the $B_2\left(21\mathrm{}068 {\mathrm{cm}}^{-1\mathrm{}}\right)$ absorption lines in ruby has been observed at 2°K. The splitting of each $B$ line is 2.8×${10}^{-5\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$/V/cm for an electric field parallel to the $c$ axis. This is a factor 3.7 larger than the corresponding splitting of the $R$ lines. There is no observable effect for fields perpendicular to the $c$ axis. Crystal-field theory satisfactorily predicts these properties, which are determined by the symmetry of the ${\mathrm{Cr}}^{3+}$ site. The point-charge model does not correctly predict the absolute value of the observed electric splitting, nor the matrix elements of the $B$ lines.