Pulsed excitation on the two-photon Cs $6{}^2{S}_{1/2}\to 7{}^2{D}_{3/2,5/2}$ transition results in time-resolved fluorescence at 697 and 672 nm. The rates for fine-structure mixing between the $7{}^2{D}_{3/2,5/2}$ states have been measured for helium and argon rare-gas collision partners. The mixing rates are very fast, $1.26\pm 0.05\times {10}^{-9} {\mathrm{cm}}^3$/atom s for He and $1.52\pm 0.05\times {10}^{-10} {\mathrm{cm}}^3$/atom s for Ar, driven by the small energy splitting and large radial distribution for the valence electron. The quenching rates are considerably slower, $6.84\pm 0.09\times {10}^{-11}$ and $2.65\pm 0.04\times {10}^{-11} {\mathrm{cm}}^3$/atom s for He and Ar, respectively. The current results are placed in context with similar rates for other alkali-metal–rare-gas collision pairs using adiabaticity arguments.

• Received 1 January 2016

DOI:https://doi.org/10.1103/PhysRevA.93.033418