Use of radiation trapping for measuring electron-impact excitation cross sections for higher resonance levels of rare-gas atoms

Radiation trapping causes the optical emission cross sections for transitions from an atomic resonance level to lower levels to be dependent on the atom number density. We have measured the optical emission cross sections for a number of heavy rare-gas resonance transitions over the pressure range of 0.04 to 30 mTorr. We compare the results with the theory of Heddle, using it to extrapolate our cross-section data to the high-pressure regime where the resonance radiation is completely reabsorbed. This allows us to obtain the apparent excitation cross section for seven resonance levels of Ne, Ar, and Kr without measuring the resonance radiation that would otherwise entail vacuum ultraviolet radiometry. In some cases, our analysis of the measured pressure dependence of the optical emission cross sections points out the need for improved transition probabilities values.