4D2→4F2excitation transfer in Li induced by collisions with Li, He, and Ar ground-state atoms

Excitation transfers between the $4{}_{}{}^2{}_{}{}^{}D$ and $4{}_{}{}^2{}_{}{}^{}F$ states of lithium are studied in a temperature-controlled heat-pipe oven. These transfers are induced by collisions with Li, He, and Ar ground-state atoms. Quenching cross section and radiative rates are also measured. For the excitation transfer process, the thermally averaged cross sections are, respectively, ${\sigma }^{\mathrm{Li}}=400\mathrm{}$ ${\mathrm{\AA }}^2$, ${\sigma }^{\mathrm{He}}=120\mathrm{}$ ${\mathrm{\AA }}^2$, and ${\sigma }^{\mathrm{Ar}}=190\mathrm{}$ ${\mathrm{\AA }}^2$. These values agree with the experimental results of Gallagher in Na and the calculations of Gersten. Finally, the behavior of the $4{}_{}{}^2{}_{}{}^{}D-4\mathrm{}{}_{}{}^2{}_{}{}^{}F$ two-level system in the $l$-mixing regime is investigated in the case of Ar collisions.