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Physical Review A

Storage-ring experiments with 10–100-keV Ca− beams: Role of blackbody radiation

Harold K. Haugen, L. H. Andersen, T. Andersen, Péter Balling, N. Hertel, Preben Hvelplund, S.P. Møller

Published Jul 1, 1992• 51 citations
Publisher

Abstract

The lifetime of 10--100-keV ${\mathrm{Ca}}^{\mathrm{\ensuremath{-}}}$ beams in a heavy-ion storage ring was measured to be \ensuremath{\sim}490 \ensuremath{\mu}s. A combination of experimental and theoretical evidence strongly suggests that the observed decay is associated with blackbody-radiation-induced photodetachment of ${\mathrm{Ca}}^{\mathrm{\ensuremath{-}}}$(4${\mathit{s}}^{2}$4p $^{2}$P) ground-state ions at room temperature. Blackbody-radiation effects may also explain the previously reported existence of a long-lived (290\ifmmode\pm\else\textpm\fi{}100 \ensuremath{\mu}s) metastable ${\mathrm{Ca}}^{\mathrm{\ensuremath{-}}}$(4s4${\mathit{p}}^{2}$ $^{4}$P) ion [D. Hanstorp et al., Phys. Rev. Lett. 63, 368 (1989)].

DOI
10.1103/physreva.46.r1

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The lifetime of 10--100-keV Ca\ensuremath−{\mathrm{Ca}}^{\mathrm{\ensuremath{-}}}Ca\ensuremath− beams in a heavy-ion storage ring was measured to be \ensuremath{\sim}490 \ensuremath{\mu}s. A combination of experimental and theoretical evidence strongly suggests that the observed decay is associated with blackbody-radiation-induced photodetachment of Ca\ensuremath−{\mathrm{Ca}}^{\mathrm{\ensuremath{-}}}Ca\ensuremath−(4s2{\mathit{s}}^{2}s24p 2^{2}2P) ground-state ions at room temperature. Blackbody-radiation effects may also explain the previously reported existence of a long-lived (290\ifmmode\pm\else\textpm\fi{}100 \ensuremath{\mu}s) metastable Ca\ensuremath−{\mathrm{Ca}}^{\mathrm{\ensuremath{-}}}Ca\ensuremath−(4s4p2{\mathit{p}}^{2}p2 4^{4}4P) ion [D. Hanstorp et al., Phys. Rev. Lett. 63, 368 (1989)].
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The lifetime of the 3P0^{3}P_{0}3P0​ state of ${\mathrm{Bi}}^{\ensuremath{-}}$ has been measured by selective photodetachment in a cryogenic ion-beam storage ring. By measuring the lifetime as a function of applied laser powers and extrapolating to zero laser power, a lifetime of $16.0\ifmmode\pm\else\textpm\fi{}0.5$ s is deduced for electric quadrupole decay of the excited state to the ground sate. The result provides a stringent test of recent state-of-the art theoretical calculations.
We theoretically investigate the collisional dynamics of laser-cooled 87Rb{}^{87}\text{Rb}87Rb ground-state atoms and 40Ca+{}^{40}{\mathrm{Ca}}^{+}40Ca+ ground-state ions in the context of the hybrid trap experiment of Hall et al. [Phys. Rev. Lett. 107, 243202 (2011)], leading to ion losses. Cold 87Rb40Ca+{}^{87}{\mathrm{Rb}}^{40}{\mathrm{Ca}}^{+}87Rb40Ca+ ground-state molecular ions are created by radiative association, and we demonstrate that they are protected against photodissociation by blackbody radiation and by the 40Ca+{}^{40}{\mathrm{Ca}}^{+}40Ca+ cooling laser at 397 nm. This paper yields an interpretation of the direct observation of 87Rb40Ca+{}^{87}{\mathrm{Rb}}^{40}{\mathrm{Ca}}^{+}87Rb40Ca+ ions in the experiment, in contrast to other hybrid trap experiments using other species. Based on an updated model for molecular spin-orbit interaction, we also confirm that the nonradiative charge-exchange is the dominant loss process for Ca+{\mathrm{Ca}}^{+}Ca+ and obtain rates in agreement with experimental observations and a previous calculation.
We study the internal state dynamics of optically trapped polyatomic molecules subject to room-temperature blackbody radiation. Using rate equations that account for radiative decay and blackbody excitation between rovibrational levels of the electronic ground state, we model the microscopic behavior of the molecules' thermalization with their environment. As an application of the model, we describe in detail the procedure used to determine the blackbody and radiative lifetimes of low-lying vibrational states in ultracold CaOH molecules, the values of which were reported in previous work [C. Hallas et al., Phys. Rev. Lett. 130, 153202 (2023)]. Ab initio calculations are performed and are found to agree with the measured values. Vibrational-state lifetimes for several other laser-coolable molecules, including SrOH and YbOH, are also calculated.