Physical Review Letters

Observation of the metastable negative argon ion Ar−

Young K. Bae, James R. Peterson, A. S. Schlachter, J. Warren Stearns

Published Feb 25, 1985• 22 citations

Abstract

The predicted metastable $^{4}\mathrm{S}_{3/2}^{\mathrm{e}}$ ${\mathrm{Ar}}^{\mathrm{\ensuremath{-}}}$ ion has been observed for the first time. It was produced from an ${\mathrm{Ar}}^{+}$ beam by two-step electron capture in Cs vapor. Decay-rate measurements favor the existence of only one state with a lifetime of 350\ifmmode\pm\else\textpm\fi{}150 ns.

DOI: 10.1103/physrevlett.54.789

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Physical Review Letters

Observation of the metastable negative argon ion Ar−

Young K. Bae, James R. Peterson, A. S. Schlachter, J. Warren Stearns

Published Feb 25, 1985• 22 citations

Publisher

Abstract

The predicted metastable

^{4}\mathrm{S}_{3/2}^{\mathrm{e}}

{\mathrm{Ar}}^{\mathrm{\ensuremath{-}}}

ion has been observed for the first time. It was produced from an

{\mathrm{Ar}}^{+}

beam by two-step electron capture in Cs vapor. Decay-rate measurements favor the existence of only one state with a lifetime of 350\ifmmode\pm\else\textpm\fi{}150 ns.

DOI: 10.1103/physrevlett.54.789

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Observation of the Molecular Helium Negative Ion He2−

Young K. Bae, M. J. Coggiola, James R. Peterson

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Formation and mean lifetime of the metastable doubly charged rare-gas dimer NeAr2+

I. Ben-Itzhak, Ilya Gertner, B. Rosner

The observation of a long-lived ${\mathrm{NeAr}}^{2+}$ molecular ion is reported. This ion was obtained by charge stripping of a 900-keV ${\mathrm{NeAr}}^{+}$ beam in an Ar gas target, and its mean lifetime was determined to be 275\ifmmode\pm\else\textpm\fi{}25 nsec. This is a direct measurement of the mean lifetime of a doubly charged rare-gas dimer. The ion decay is decribed well by a single exponential decay, suggesting that only one metastable state is populated in the collision. The cross section for the ${\mathrm{NeAr}}^{2+}$ production was determined to be (3\ifmmode\pm\else\textpm\fi{}2)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}18}$ ${\mathrm{cm}}^{2}$ . The existence of this weakly bound molecular ion and the fact that its mean lifetime is known can serve to motivate better theoretical calculations of molecular structure and the dissociation process.The observation of a long-lived ${\mathrm{NeAr}}^{2+}$ molecular ion is reported. This ion was obtained by charge stripping of a 900-keV ${\mathrm{NeAr}}^{+}$ beam in an Ar gas target, and its mean lifetime was determined to be 275\ifmmode\pm\else\textpm\fi{}25 nsec. This is a direct measurement of the mean lifetime of a doubly charged rare-gas dimer. The ion decay is decribed well by a single exponential decay, suggesting that only one metastable state is populated in the collision. The cross section for the ${\mathrm{NeAr}}^{2+}$ production was determined to be (3\ifmmode\pm\else\textpm\fi{}2)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}18}$ ${\mathrm{cm}}^{2}$. The existence of this weakly bound molecular ion and the fact that its mean lifetime is known can serve to motivate better theoretical calculations of molecular structure and the dissociation process.

Physical Review AJan 1, 199316 citations

The predicted metastable

^{4}\mathrm{S}_{3/2}^{\mathrm{e}}

{\mathrm{Ar}}^{\mathrm{\ensuremath{-}}}

ion has been observed for the first time. It was produced from an

{\mathrm{Ar}}^{+}

beam by two-step electron capture in Cs vapor. Decay-rate measurements favor the existence of only one state with a lifetime of 350\ifmmode\pm\else\textpm\fi{}150 ns.

Long-lived metastable ${\mathrm{He}}_{2}^{\ensuremath{-}}$ negative ions have been observed for the first time. They were produced from

{\mathrm{He}}_{2}^{+}

by two-step electron capture in a Cs vapor target. The apparent autodetachment decay rates have been measured at several delay times after formation, and indicate the presence of more than one state, with the lifetime of the major component exceeding 100 \ensuremath{\mu}s. The most likely configurations are ${^{4}\ensuremath{\Sigma}_{g}}^{+}$ and/or $^{4}\ensuremath{\Pi}_{g}$ states bound below ${\mathrm{He}}_{2}({^{3}\ensuremath{\Sigma}_{g}}^{+})$.

The natural lifetime of the metastable

4d\phantom{\rule{0.2em}{0ex}}^{2}D_{5∕2}

state in

^{88}\mathrm{Sr}^{+}

has been measured using a single laser-cooled, trapped ion. The ion was prepared in the

4d\phantom{\rule{0.2em}{0ex}}^{2}D_{5∕2}

state by laser excitation of the $5s\phantom{\rule{0.2em}{0ex}}^{2}S_{1∕2}\ensuremath{-}4d\phantom{\rule{0.2em}{0ex}}^{2}D_{5∕2}$ quadrupole transition at 674 nm. The decay time was measured by using Dehmelt's electron shelving method to monitor the ion's electronic state. Two separate investigations were conducted under slightly different experimental conditions. 160 000 decay times from the

4d\phantom{\rule{0.2em}{0ex}}^{2}D_{5∕2}

state were observed in total, and two different methods for determining the statistical value of the measured lifetime have been compared. Systematic effects have also been estimated, and including these effects yields a value of $\ensuremath{\tau}=390.8(1.6)\phantom{\rule{0.3em}{0ex}}\mathrm{ms}$ ($1\ensuremath{\sigma}$ uncertainty) for the natural lifetime.

{3p}^{5}4s{}^{3}{P}_{2}^{o}

state of neutral argon. Our calculations, based on many-body perturbation theory, yield a binding energy of 24.9 meV. As a test of the present computational method, we also include the results of a comparative study of ${\mathrm{Ca}}^{\ensuremath{-}}$.

The lifetime of the metastable autodetaching 1s2s2p

^{4}

{\mathit{P}}_{5/2}

level of the $^{4}\mathrm{He}^{\mathrm{\ensuremath{-}}}$ ion has been measured by a time-of-flight technique to be 350\ifmmode\pm\else\textpm\fi{}15 \ensuremath{\mu}s using a heavy-ion storage ring. Blackbody-induced photodetachment of this weakly bound level is shown to influence the decay rate by nearly 20%, an effect not discussed previously. The magnetic-field-induced mixing effects provide additional information about the lifetime of the close-lying

^{4}

{\mathit{P}}_{3/2}

level, yielding \ensuremath{\tau}

{(}^{4}

{\mathit{P}}_{3/2}

)=12\ifmmode\pm\else\textpm\fi{}2 \ensuremath{\mu}s. The observed lifetimes are consistent with previous experimental values, but the accuracy of the

^{4}

{\mathit{P}}_{5/2}

lifetime is improved by a factor of 6, allowing a detailed test of theoretical predictions to be performed. The

^{4}

{\mathit{P}}_{5/2}

lifetime is significantly shorter than most recent advanced theoretical results, but in agreement with a multiconfiguration Hartree-Fock approach accurately describing the initial bound

^{4}

{\mathit{P}}_{5/2}

and the final continuum

^{2}

{\mathit{F}}_{5/2}

states.

The observation of a long-lived

{\mathrm{NeAr}}^{2+}

molecular ion is reported. This ion was obtained by charge stripping of a 900-keV

{\mathrm{NeAr}}^{+}

beam in an Ar gas target, and its mean lifetime was determined to be 275\ifmmode\pm\else\textpm\fi{}25 nsec. This is a direct measurement of the mean lifetime of a doubly charged rare-gas dimer. The ion decay is decribed well by a single exponential decay, suggesting that only one metastable state is populated in the collision. The cross section for the

{\mathrm{NeAr}}^{2+}

production was determined to be (3\ifmmode\pm\else\textpm\fi{}2)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}18}$

{\mathrm{cm}}^{2}

. The existence of this weakly bound molecular ion and the fact that its mean lifetime is known can serve to motivate better theoretical calculations of molecular structure and the dissociation process.