Rubidium and Cesium Excitation Transfer in Nearly Adiabatic Collisions with Inert Gases

The cross sections for rubidium $5{}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}\rightleftarrows 5{}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$ and cesium $6{}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}\rightleftarrows 6{}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}$ excitation transfer due to inert-gas collisions have been measured. The temperature of the collision vessel has been varied from 300°K to 900°K in order to partially establish the velocity dependence of these cross sections (the alkali resonance-line optical depths were always much less than 1). The various cross sections exhibit a systematic behavior that can be combined to find the general shape of a "universal" cross section that ranges across six orders of magnitude, starting just below the threshold for "sudden" collisions. The surprisingly large influence of optical line broadening on these excitation-transfer measurements has been removed as a source of error.