Electron-Impact Excitation of the $6{}_{}{}^2{}_{}{}^{}P$ States in Cesium

The ratio of the differential cross sections at zero-angle scattering for the excitation of the $6{}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}$ and $6{}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$ states in Cs has been measured for incident-electron energies between 3 and 68 eV. At 68-eV incident-electron energy the ratio is found to be 1.85, as predicted from degeneracy, but decreases significantly below 20-eV incident-electron energy.