Cross sections of excitation transfer between the fine-structure sublevels of Cs(7 2 P), Rb(6 2 P) and Rb(7 2 P) induced by collisions with rare-gas atoms have been determined from the time dependence of the sensitised fluorescence. The Cs and Rb atoms, contained in absorption cells filled with inert gases at different pressures, were excited using a pulsed dye laser pumped by a nitrogen laser. The fluorescence was observed time resolved employing a photon counting technique. The use of a two-level approximation allowed the Maxwellian (velocity) averaged transfer cross sections to be calculated. Comparison of the cross section values determined in this work with the values quoted by other authors shows good consistency in the case of Rb 6 2 P inert-gas collisions while in the case of Cs 7 2 P inert-gas collisions there are some discrepancies. Rb 7 2 P excitation transfer has not been dealt with before.
The temperature dependence of cross sections for 52P1/2 ↔ 52P3/2 excitation transfer in rubidium, induced in collisions with CH4, CH2D2, and CD4 molecules, has been investigated using methods of sensitized fluorescence over a temperature range 300–650 K. The cross sections, which are of the order of 30 Å2 and which exceed similar cross sections for collisions with noble gas atoms by at least two orders of magnitude, exhibit an isotope effect which is ascribed to the phenomenon of electronic-to-rotational energy transfer.
The 8
2S state of rubidium is selectively populated by stepwise excitation using light from a rubidium lamp and a tunable dye laser. Excitation transfer from the 8
2S to the 6
2D state is studied in a glass cell containing rubidium vapor and noble-gas atoms at different pressures and ground-state rubidium atoms as perturbers. The thermally averaged cross sections for excitation transfer (in units of ${10}^{\mathrm{\ensuremath{-}}15}$
cm2) are 0.13\ifmmode\pm\else\textpm\fi{}0.05, 3.0\ifmmode\pm\else\textpm\fi{}1.2, 2.2\ifmmode\pm\else\textpm\fi{}0.9, 1.7\ifmmode\pm\else\textpm\fi{}0.7, and 4.3\ifmmode\pm\else\textpm\fi{}2.6 for the noble gases He, Ne, Ar, Kr, and Xe, respectively, and (6.7\ifmmode\pm\else\textpm\fi{}3.0)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}13}$
cm2 for rubidium atoms. The results show that the excitation-transfer cross sections for intermediately excited states cannot be accurately scaled from simple models.