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Physical Review A

4D2→4F2 excitation transfer in Li induced by collisions with Li, He, and Ar ground-state atoms

Bernard Dubreuil, Catherine Chaleard

Published Feb 1, 1984• 10 citations
Publisher

Abstract

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, ${\ensuremath{\sigma}}^{\mathrm{Li}}=400$ ${\mathrm{\AA{}}}^{2}$, ${\ensuremath{\sigma}}^{\mathrm{He}}=120$ ${\mathrm{\AA{}}}^{2}$, and ${\ensuremath{\sigma}}^{\mathrm{Ar}}=190$ ${\mathrm{\AA{}}}^{2}$. These values agree with the experimental results of Gallagher in Na and the calculations of Gersten. Finally, the behavior of the $4^{2}D\ensuremath{-}4^{2}F$ two-level system in the $l$-mixing regime is investigated in the case of Ar collisions.

DOI
10.1103/physreva.29.958

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l-mixing collisions Li(n2{n}^{2}n2D)+X\ensuremath{\rightarrow}Li(n2{n}^{2}n2L,L>2)+X induced in Rydberg states of lithium (n=4,5,...,13) by rare-gas atoms or Li ground-state atoms are studied in a heat-pipe arrangement. The l-mixing cross sections deduced from the time analysis of the n2{n}^{2}n2D laser-induced fluorescence agree with experimental values obtained with the heavier alkali-metal atoms and with different theoretical models developed for quasielastic Rydberg-electron--target collisions. Quenching of the n2{n}^{2}n2D fluorescence at higher rare-gas pressures is interpreted as inelastic collisional transfer of the L\ensuremath{\ge}1 mixed states to the nonhydrogenic S sublevel. Finally the radiative lifetimes of the n2{n}^{2}n2D states and n2{n}^{2}n2L mixed states with L\ensuremath{\ge}1 are deduced, respectively, from the low-pressure limit and intermediate-pressure study of the n2{n}^{2}n2D fluorescence relaxation rate.
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Two-step laser-induced-fluorescence techniques are used to investigate nnn-changing collisional processes $\mathrm{Li}(n=9)+\mathrm{Li}(2^{2}S)\ensuremath{\rightarrow}\mathrm{Li}({n}^{\ensuremath{'}}\ensuremath{\ne}n) +\mathrm{Li}(2^{2}S)+\ensuremath{\Delta}E_{\mathrm{nn}}^{\ensuremath{'}}$ in a temperature-controlled lithium heat-pipe oven. Numerical identification of the resonance- and collision-induced fluorescences with the hydrogenic rate equations describing the time variation of the n=7,8,9,10,11n=7,8,9,10,11n=7,8,9,10,11 populations allows the determination of collisional transfer and quenching rate coefficients. nnn-changing collisions with $\ensuremath{\Delta}n=|n\ensuremath{-}{n}^{\ensuremath{'}}|=1$ predominate, and the quenching rate coefficients are found nearly independent of $n: {k}_{n}\ensuremath{\sim}1.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}$ cm3{\mathrm{cm}}^{3}cm3${\mathrm{s}}^{\ensuremath{-}1}$.