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Optics and Spectroscopy

Inelastic Transitions Between the Fine-Structure Components of Alkali-Metal Atoms in the Case of Adiabatic Collisions. II. Calculations of Cross Sections

E. I. Dashevskaya, E. E. Nikitin

Published Jun 1, 1967• 11 citations
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For years, inelastic, fine-structure-changing collisions between excited alkali-metal atoms and noble-gas perturbers have been a source of information on the alkali-metal--noble-gas interaction. Here, we consider the role of elastic fine-structure-mixing collisions on alkali-metal absorption cross sections. Specifically, we consider the four optical hyperfine transitions of the ${D}_{1}$ absorption spectrum for $^{87}\mathrm{Rb}$, and in particular the doublet corresponding to $5^{2}S_{1/2}({F}_{g}=2)\ensuremath{-}5^{2}P_{1/2}({F}_{e}=1,2)$ transitions. Although ideally the amplitudes of the doublet's absorption cross sections are identical, we find that fine-structure mixing of ${D}_{2}$ oscillator strength into the ${D}_{1}$ spectrum breaks the cross sections' equality and leads to doublet asymmetry. We obtain a fine-structure mixing parameter $\ensuremath{\lambda}$ of $(5.4\ifmmode\pm\else\textpm\fi{}0.3)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}21}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{3}$, and estimate a $5^{2}P_{1/2}$ hyperfine-splitting density shift $\ensuremath{\zeta}$ in the $^{87}\mathrm{Rb}$-Xe system of $+0.71\ifmmode\pm\else\textpm\fi{}0.03\phantom{\rule{0.16em}{0ex}}\mathrm{GHz}/\mathrm{amagat}$. These results have implications for spectroscopic applications of the $^{87}\mathrm{Rb}$ isoclinic point, which we consider as part of our conclusions.

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We have measured cold titanium-helium collisions that cause transitions between the fine-structure levels of the $[3{d}^{2}4{s}^{2}]\phantom{\rule{0.3em}{0ex}}^{3}F_{J}$ electronic ground state of atomic titanium, over a temperature range from 5 to $20\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The $\mathrm{Ti}\text{\ensuremath{-}}\mathrm{He}$ inelastic collision cross section is significantly smaller than cross sections measured for collisions of non-transition-metal atoms with noble gas atoms. Our theoretical calculations of the inelastic cross sections reproduce the magnitude and temperature dependence of the measurements, and attribute the suppression of inelastic collisions to titanium's ``submerged'' $d$-shell valence electrons.

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Mechanism of the excitation of alkali metal atoms in slow collisions

E. E. Nikitin, Anatoly I. Shushin

OptSp•Sep 1, 1977•0 citations
For years, inelastic, fine-structure-changing collisions between excited alkali-metal atoms and noble-gas perturbers have been a source of information on the alkali-metal--noble-gas interaction. Here, we consider the role of elastic fine-structure-mixing collisions on alkali-metal absorption cross sections. Specifically, we consider the four optical hyperfine transitions of the D1{D}_{1}D1​ absorption spectrum for 87Rb^{87}\mathrm{Rb}87Rb, and in particular the doublet corresponding to $5^{2}S_{1/2}({F}_{g}=2)\ensuremath{-}5^{2}P_{1/2}({F}_{e}=1,2)$ transitions. Although ideally the amplitudes of the doublet's absorption cross sections are identical, we find that fine-structure mixing of D2{D}_{2}D2​ oscillator strength into the D1{D}_{1}D1​ spectrum breaks the cross sections' equality and leads to doublet asymmetry. We obtain a fine-structure mixing parameter $\ensuremath{\lambda}$ of $(5.4\ifmmode\pm\else\textpm\fi{}0.3)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}21}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{3}$, and estimate a 52P1/25^{2}P_{1/2}52P1/2​ hyperfine-splitting density shift $\ensuremath{\zeta}$ in the 87Rb^{87}\mathrm{Rb}87Rb-Xe system of $+0.71\ifmmode\pm\else\textpm\fi{}0.03\phantom{\rule{0.16em}{0ex}}\mathrm{GHz}/\mathrm{amagat}$. These results have implications for spectroscopic applications of the 87Rb^{87}\mathrm{Rb}87Rb isoclinic point, which we consider as part of our conclusions.
We have measured cold titanium-helium collisions that cause transitions between the fine-structure levels of the [3d24s2]3FJ[3{d}^{2}4{s}^{2}]\phantom{\rule{0.3em}{0ex}}^{3}F_{J}[3d24s2]3FJ​ electronic ground state of atomic titanium, over a temperature range from 5 to 20K20\phantom{\rule{0.3em}{0ex}}\mathrm{K}20K. The $\mathrm{Ti}\text{\ensuremath{-}}\mathrm{He}$ inelastic collision cross section is significantly smaller than cross sections measured for collisions of non-transition-metal atoms with noble gas atoms. Our theoretical calculations of the inelastic cross sections reproduce the magnitude and temperature dependence of the measurements, and attribute the suppression of inelastic collisions to titanium's ``submerged'' ddd-shell valence electrons.