The authors have measured the cross sections for the collisional quenching of highly excited (34<or=n<or=43) S rubidium atoms by ground-state rubidium atoms. The comparison between their data and the values calculated using a theoretical approach that only takes into account the valence electron-ground-state rubidium interaction provides the first experimental estimation of the cross section for the elastic scattering of ultra-low-energy electrons (E approximately=0.01 eV) by rubidium atoms. Their results for the quenching are connected to the available measurements of the self-broadening of the rubidium (5S-nS) lines by using a recent theoretical model: for n approximately 40 the self-broadcasting is essentially due to inelastic collisions. An upper limit is given for the cross section for the isotopic transfer between 85 Rb(nS) and 87 Rb(nS) states due to collisions with ground-state rubidium atoms.
An experiment is described which measures the collision cross section for transfer of excitation in rubidium by helium. Rubidium atoms are pumped to either the
2P21 or
2P23 state by irradiation with one of the resonance lines. Some excited rubidium atoms are transferred to the other
P state by collisions with helium atoms. The rubidium atoms then radiate both resonance lines. Measurements of the intensities of both resonance lines as a function of helium pressure are used to calculate the collision cross section. The cross section for
2P21 to
2P23 is 1.0\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}17}$
cm2\ifmmode\pm\else\textpm\fi{}10% and for
2P23 to
2P21 is 1.2\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}17}$
cm2\ifmmode\pm\else\textpm\fi{}10%.
The electronic excitation transfer processes, $\mathrm{K}(^{2}P_{\frac{1}{2}})\ensuremath{\rightarrow}\mathrm{Rb}(^{2}S_{\frac{1}{2}})\ensuremath{\rightarrow}\mathrm{K}(^{2}S_{\frac{1}{2}})+\mathrm{Rb}(^{2}P_{\frac{1}{2}})+\ensuremath{\Delta}E$ and $\mathrm{K}(^{2}P_{\frac{3}{2}})+\mathrm{Rb}(^{2}S_{\frac{1}{2}})\ensuremath{\rightarrow}\mathrm{K}(^{2}S_{\frac{1}{2}})+\mathrm{Rb}(^{2}P_{\frac{1}{2}})+\ensuremath{\Delta}E$ have been studied by irradiating a cell containing a nonequilibrium mixture of potassium and rubidium vapors with either the 7665 \AA{} D2 line or the 7699 \AA{} D1 line of the potassium resonance doublet. The resulting collisionally induced rubidium 7948 \AA{} fluorescence signal, isolated by interference filters used in tandem, is detected with a liquid-nitrogen-cooled $S\ensuremath{-}1$ photo-multiplier placed at right angles to the direction of excitation. Measurements of the intensity ratio of the potassium and rubidium fluoresence combined with an optical absorption determination of the rubidium atom density yields the following excitation transfer cross sections: $Q[\mathrm{K}(^{2}P_{\frac{1}{2}})\ensuremath{\rightarrow}\mathrm{Rb}(^{2}P_{\frac{1}{2}})]=2.2 {\AA{}}^{2}\ifmmode\pm\else\textpm\fi{}25%$ and $Q[\mathrm{K}(^{2}P_{\frac{3}{2}})\ensuremath{\rightarrow}\mathrm{Rb}(^{2}P_{\frac{1}{2}})]=2.6 {\AA{}}^{2}\ifmmode\pm\else\textpm\fi{}20%$ at $T=365\ifmmode^\circ\else\textdegree\fi{}\mathrm{K}\ifmmode\pm\else\textpm\fi{}2%$. Throughout an experimental run the potassium and rubidium vapor pressures are varied, but data are taken for only the lowest vapor pressures for which corrections due to resonance radiation imprisonment are unnecessary.