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Physical Review A

6pP2 levels of ionized barium: Lifetimes and depolarization cross sections

F. M. Kelly, M. S. Mathur

Published Nov 1, 1978• 7 citations
Publisher

Abstract

The Hanle effect and its variation with density has been used to determine the depolarization cross section for collisions between the $^{2}P_{\frac{3}{2}}$ barium ions and neutral atoms. An extrapolation of the data to zero density gives a value of the average lifetime $\ensuremath{\tau}=6.22$ ns for the $6p^{2}P_{\frac{3}{2}}$ level. A further experiment gives $\ensuremath{\tau}=7.55$ ns for the $6p^{2}P_{\frac{1}{2}}$ level.

DOI
10.1103/physreva.18.2135

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Physical Review A•Aug 1, 1976•34 citations
The Hanle effect and its variation with density has been used to determine the depolarization cross section for collisions between the 2P32^{2}P_{\frac{3}{2}}2P23​​ barium ions and neutral atoms. An extrapolation of the data to zero density gives a value of the average lifetime \ensuremathτ=6.22\ensuremath{\tau}=6.22\ensuremathτ=6.22 ns for the 6p2P326p^{2}P_{\frac{3}{2}}6p2P23​​ level. A further experiment gives \ensuremathτ=7.55\ensuremath{\tau}=7.55\ensuremathτ=7.55 ns for the 6p2P126p^{2}P_{\frac{1}{2}}6p2P21​​ level.
The change in the Hanle effect of the singlet resonance line of neutral barium has been studied over a wide range of density. The low density region has been used to confirm a lifetime of 8.37 ± 0.08 ns for the 6s6p1P1 level. We have determined the cross sections for the relaxation of the multipole moment of order 2 for collisions of the excited level with the ground level and with the metastable 6s5d1D2 level, and comparisons are made with the measured value of [Formula: see text] for the ground level with theoretical predictions.
The lifetime of the Ca+{\mathrm{Ca}}^{+}Ca+ 42P324^{2}P_{\frac{3}{2}}42P23​​ state and that of the Mg+{\mathrm{Mg}}^{+}Mg+ 32P323^{2}P_{\frac{3}{2}}32P23​​ state have been measured by the Hanle-effect method with optical excitation from the ground states of the ions. The lifetimes are, respectively, (6.72\ifmmode\pm\else\textpm\fi{}0.20)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}9}$ and (3.67\ifmmode\pm\else\textpm\fi{}0.18)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}9}$ sec. The ions were produced by introducing traces of calcium or magnesium into an argon discharge. "Alignment" depolarization cross sections $\ensuremath{\sigma}$ were obtained for the collisional depolarization of the following states of calcium and magnesium due to collisions with argon: $\ensuremath{\sigma}(\mathrm{Ca} 4^{1}P_{1} \mathrm{state})=(1.9\ifmmode\pm\else\textpm\fi{}0.3)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}14}{\mathrm{cm}}^{2};$ $\ensuremath{\sigma}({\mathrm{Ca}}^{+} 4^{2}P_{\frac{3}{2}} \mathrm{state})=(1.4\ifmmode\pm\else\textpm\fi{}0.2)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}14}{\mathrm{cm}}^{2};$ $\ensuremath{\sigma}(\mathrm{Mg} 3^{1}P_{1} \mathrm{state})=(1.9\ifmmode\pm\else\textpm\fi{}0.3){10}^{\ensuremath{-}14}{\mathrm{cm}}^{2};$ $\ensuremath{\sigma}({\mathrm{Mg}}^{+} 3^{2}P_{\frac{3}{2}} \mathrm{state})=(1.3\ifmmode\pm\else\textpm\fi{}0.25)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}14}{\mathrm{cm}}^{2}.$The magnitudes of these cross sections are in accord with the theories of Byron and Foley and of Omont; we give a discussion of the extension of these theories to include ion-atom collisions.
The lifetimes of the 5p2P325p^{2}P_{\frac{3}{2}}5p2P23​​ and 5p2P125p^{2}P_{\frac{1}{2}}5p2P21​​ states of Sr+{\mathrm{Sr}}^{+}Sr+ and the 6p2P326p^{2}P_{\frac{3}{2}}6p2P23​​ and 6p2P126p^{2}P_{\frac{1}{2}}6p2P21​​ states of Ba+{\mathrm{Ba}}^{+}Ba+ have been measured by the Hanle-effect technique with optical excitation from the ion ground state. (The lifetimes of the Mg+{\mathrm{Mg}}^{+}Mg+ 3p2P323p^{2}P_{\frac{3}{2}}3p2P23​​ and Ca+{\mathrm{Ca}}^{+}Ca+ 4p2P324p^{2}P_{\frac{3}{2}}4p2P23​​ states were obtained by the same technique and reported previously.) These Ca+{\mathrm{Ca}}^{+}Ca+, Sr+{\mathrm{Sr}}^{+}Sr+, and Ba+{\mathrm{Ba}}^{+}Ba+ states each decay to a 2D32,52^{2}D_{\frac{3}{2},\frac{5}{2}}2D23​,25​​ doublet as well as to the ground 2S12^{2}S_{\frac{1}{2}}2S21​​ state, and the branching ratios for these transitions have been measured. The ions were produced by introducing traces of the atomic vapor into an argon discharge. Consequently, the cross sections for collisional depolarization of these 2PJ^{2}P_{J}2PJ​ states due to collisions with argon were also obtained from the measurements. The experimental results are given in Tables I and II. A discussion of the ion-atom collisional depolarization cross sections is included.
The radiative lifetimes of the 17992-,25068-,28857-, 37414-, 40564-, and 44017-${\mathrm{cm}}^{\ensuremath{-}1}$ neutral levels and the 30392-${\mathrm{cm}}^{\ensuremath{-}1}$ ion level of Yb have been measured by the Hanle method in a fast-flowing He system. The lifetimes (in units of ${10}^{\ensuremath{-}9}$ sec) were found to be 820(20), 5.12(0.12), 14.4(0.4), 77.4(6.0), 9.32(0.6), 39.1(3.5), and 5.8(0.6), respectively. In a flowing system with He as a buffer gas the alignment depolarization cross sections with Yb were obtained and are reported here for the first time. They are (in units of ${10}^{\ensuremath{-}15}$ cm2{\mathrm{cm}}^{2}cm2) 5.0(1.0), 5.9(1.0), 5.9(1.2), 17.9(2.0), 28.2(3.0), 5.16(4.0), and 7.2(2.5), respectively.