Fine-structure-changing collision cross sections within the low-lyingnD2states of rubidium induced by ground-state rubidium atoms

The thermal cross sections for inelastic transfer of excited rubidium atoms from the $n{}_{}{}^2{}_{}{}^{}D_{\frac{5}{2}}^{}{}_{}{}^{}$ to the $n{}_{}{}^2{}_{}{}^{}D_{\frac{3}{2}}^{}{}_{}{}^{}$ fine-structure state caused by fine-structure-changing collisions with ground-state rubidium atoms have been measured by selective stepwise excitation of the rubidium atoms and observation of the resulting fluorescence. The cross sections (in units of ${10}^{-14\mathrm{}}$ ${\mathrm{cm}}^2$) for $n$ being 5-9 are 2.9±0.6, 6.9±1.4, 11.5±2.3, 17.1±3.0, and 26.0±5.0, respectively. The fine-structure-changing cross sections are of the order of the geometrical cross sections and increase slightly less than ${\left(n^{*}\right)}^4$ for the low-lying $n{}_{}{}^2{}_{}{}^{}D$ states studied.