Cross sections for electron-impact excitation of Krypton

Electron-impact excitation cross sections for Kr have been measured by means of the optical method over a range of incident-electron energies between onset and 250 eV. By measuring cascade transitions into the 4p(5)5p levels from higher-lying levels and subtracting this contribution from the observed transitions out of the 4p(5)5p levels, we are able to determine the cross sections for direct electron excitation into the ten levels of the 4p(5)5p configuration (2p in Paschen's notation). The general trends of these cross sections for Kr are compared with previous measurements from our labs on Ne, Ar, and Xe. We note that the optical emission cross sections for transitions from levels resonant with the ground level vary with gas pressure. Fitting this observed pressure dependence to a simple model allows us to test theoretical values of the transition coefficients for these levels.