Ultraviolet emission cross sections for neutral argon--argon and krypton--krypton collisions

Measurements of the absolute total ultraviolet (UV) emission cross sections for ground state argon-argon and krypton-krypton atomic collisions have been made over an energy interval from threshold to 150 eV in the center-of-mass (cm) system. Additionally, emission cross sections for the lowest resonance state radiations have been individually measured from 30 to 150 eV cm for Ar + Ar collisions and from 80 to 150 eV cm for Kr + Kr collisions. These cross sections were determined from the detection of uv radiation emitted in solid angles centered 900 to the neutral atom beam axis. The effect of trace numbers of metastable atoms in the incident neutral beam on the total uv cross section has been examined near the threshold for uv production. UV emission thresholds for ground state collisions equal to 18 and 17 eV were observed for Ar + Ar and Kr + Kr collisions, respectively. For much of the collision energy interval studied, the total uv emission cross sections, sigma(uv), were larger in magnitude by a constant factor than the corresponding total ionization cross sections, sigma/sub -/. For the Ar + Ar collisions sigma(uv) = 1.2 sigma/sub -/ and for the Kr + Kr collisions sigma(uv) = 4.5 sigma/sub -/. Additionally it was found that the ratios of the individual resonance emission cross sections were constant over the interval of collision energies examined. For Ar + Ar the ratio for the lowest radiative excited states was determined to be sigma (104.8 nm)/sigma (106.7 nm) = 0.71, and for Kr + Kr collisions, sigma (116.5 nm)/sigma (123.6 nm) = 0.22. The above results have been compared to pertinent experimental work and to an electron promotion model for collisional excitation