Inelastic collisional processes in fine-structure-state mixing have been studied by selective stepwise excitation and observation of the resulting fluorescence during collisions of excited rubidium
62D25 state atoms with various noble-gas atoms. It is shown that for intermediately excited rubidium atoms the fine-structure-state mixing cross sections are generally increasing from helium to xexon. The cross sections for the process $\mathrm{Rb}(6^{2}D_{\frac{5}{2}})+A(n^{1}S_{0})\ensuremath{\rightarrow}\mathrm{Rb}(6^{2}D_{\frac{3}{2}})+A(n^{1}S_{0})+\ensuremath{\Delta}E$ have the values ${\ensuremath{\sigma}}_{\mathrm{fs}}^{*}=2.4\ifmmode\pm\else\textpm\fi{}0.9, 3.1\ifmmode\pm\else\textpm\fi{}1.2, 2.6\ifmmode\pm\else\textpm\fi{}1.0, 5.8\ifmmode\pm\else\textpm\fi{}2.2, \mathrm{and} 9.3\ifmmode\pm\else\textpm\fi{}5.6$ in units of ${10}^{\ensuremath{-}14}$
cm2, where
A denotes in sequence any one of the noble gas atoms He, Ne, Ar, Kr, and Xe, respectively. Transfer cross sections for the transfer of excited Rb
62D-state atoms out of the doublet were also determined and are about an order of magnitude smaller than the fine-structure-mixing cross sections.
The total quenching cross sections for $\mathrm{He}({n}^{1,3}S)(2\ensuremath{\le}n\ensuremath{\le}11)$ states by thermal collisions [600(+ 200, - 100) K] with He, Ne, Ar, Kr, and Xe have been measured. The main quenching mechanism is attributed to Penning ionization for lower
n, and collisional angular-momentum transfer for highly excited states. Measured cross sections are of the order of ${10}^{\ensuremath{-}15}$ to ${10}^{\ensuremath{-}14}$,
cm2. The values for higher
n states are much smaller than the geometrical cross section; this is explained by a relatively large energy spread between the
S state and $l\ensuremath{\ge}1$ states.
Cross sections for the transfer of excitation between fine-structure sublevels of the 9D state of caesium due to collisions with noble-gas atoms are measured. The experimental method employs stepwise excitation with a pulsed dye laser in the second step (6 2 P 3/2 to 9 2 D 5/2 ) and time-resolved detection of sensitised fluorescence 9 2 D 3/2 to 6 2 P 1/2 . The cross sections for the process Cs(9 2 D 3/2 )+A to Cs(9 2 D 5/2 )+A are (in units of 10 -14 cm 2 ) 7.6(1.5), 2.5(5), 2.7(5), 3.0(6) and 3.2(6) for A=He, Ne, Ar, Kr and Xe, respectively. For all the noble gases except helium the experimental cross sections are a few times smaller than the ones obtained in a recent semiclassical calculation.