Collisional energy transfer between excited-state strontium and noble-gas atoms

Inert-gas-induced collisional transfer between the first four excited states of Sr has been measured by determining excited-state densities following pulsed laser excitation of the 5 ${}_{}{}^1{}_{}{}^{}$P state. We observe 5 ${}_{}{}^1{}_{}{}^{}$P collisional transfer exclusively to the 4 ${}_{}{}^3{}_{}{}^{}$D state, with (∼800 K) rate coefficients ranging from 0.24 to 2.0×${10}^{\mathrm{-}11}$ ${\mathrm{cm}}^3$ ${\mathrm{s}}^{\mathrm{-}1}$ for the various gases. We also measure 4 ${}_{}{}^1{}_{}{}^{}$ ${\mathit{D}}_2$ transfer primarily to the 4 ${}_{}{}^3{}_{}{}^{}$D state, with rate coefficients of 0.65 to 6.8×${10}^{\mathrm{-}11}$ ${\mathrm{cm}}^3$ ${\mathrm{s}}^{\mathrm{-}1}$. The 4 ${}_{}{}^3{}_{}{}^{}$D state radiative lifetime is observed to be 2.9±0.2 μs, collisional mixing between the 4 ${}_{}{}^3{}_{}{}^{}$ ${\mathit{D}}_{\mathit{j}}$ fine-structure levels is essentially gas kinetic (k∼5×${10}^{\mathrm{-}10}$ ${\mathrm{cm}}^3$ ${\mathrm{s}}^{\mathrm{-}1}$), and k<${10}^{\mathrm{-}13}$ ${\mathrm{cm}}^3$ ${\mathrm{s}}^{\mathrm{-}1}$ for 4 ${}_{}{}^3{}_{}{}^{}$D→5 ${}_{}{}^3{}_{}{}^{}$P collisional transfer.