Collisional energy transfer between excited Sr atoms

The following energy-transfer reactions have been observed in a Sr vapor following pulsed excitation of the 5 ${}_{}{}^1{}_{}{}^{}$ ${\mathit{P}}_1$ state: ${\mathrm{Sr}}^{\mathrm{*}}$(5 ${}_{}{}^1{}_{}{}^{}$ ${\mathit{P}}_1$)+${\mathrm{Sr}}^{\mathrm{*}}$(5 ${}_{}{}^1{}_{}{}^{}$ ${\mathit{P}}_1$)→Sr(5 ${}_{}{}^1{}_{}{}^{}$ ${\mathit{S}}_0$)+${\mathrm{Sr}}^{\mathrm{*}\mathrm{*}}$(${\mathit{n}}^{2\mathit{S}+1\mathrm{}}$L)-ΔE, ${\mathrm{Sr}}^{\mathrm{*}}$(4 ${}_{}{}^1{}_{}{}^{}$ ${\mathit{D}}_2$) +${\mathrm{Sr}}^{\mathrm{*}}$(4 ${}_{}{}^1{}_{}{}^{}$ ${\mathit{D}}_2$)→Sr(5 ${}_{}{}^1{}_{}{}^{}$ ${\mathit{S}}_0$)+${\mathrm{Sr}}^{\mathrm{*}\mathrm{*}}$(${\mathit{n}}^{2\mathit{S}+1\mathrm{}}$L)-ΔE. The 4 ${}_{}{}^1{}_{}{}^{}$ ${\mathit{D}}_2$ state was populated by a nonlinear stimulated process. By measuring the rate coefficients for these reactions for over 40 final states ${\mathit{n}}^{2\mathit{S}+1\mathrm{}}$L, we look for insight into how these reactions depend on energy defect, spin, and angular momentum. It is found that there is not a very strong dependence on the energy defect, and that singlet and triplet final states are produced in comparable amounts. The final states tend to be populated more effectively as their angular momentum increases. Total rate coefficients are of the order of gas-kinetic rates.