Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Quadrupole moments and hyperfine constants of metastable states of
  Ca$^+$, Sr$^+$, Ba$^+$, Yb$^+$, Hg$^+$, and Au   Atomic quadrupole moments and hyperfine constants of the metastable $^2
D_{3/2, 5/2}$ states of Ca$^+$, Sr$^+$, Ba$^+$, Yb$^+$, and Hg$^+$ are
calculated by the multiconfiguration Dirac-Hartree-Fock and relativistic
configuration-interaction methods. For Hg$^+$, the configuration is $5d^9
6s^2$. For the other ions, the configuration consists of a single $d$-electron
outside a set of closed shells. Current interest in the quadrupole moments of
these states is due to the fact that optical transitions of these ions may be
useful as references for frequency standards. Energy shifts of the metastable
states due to the interactions of the quadrupole moments with external electric
field gradients are among the largest sources of error in these frequency
standards. For the quadrupole moments, agreement is obtained to within about
10~% with the available measurements. For the hyperfine constants, good
agreement is obtained with measurements and with other calculations, except for
the $A$ factors of the $^2D_{5/2}$ states of Sr$^+$, Ba$^+$, and Yb$^+$, where
the correlation effects are so large that they reverse the sign of the constant
relative to the Dirac-Hartree-Fock value. As a test of the Hg$^+$ calculational
methods, quadrupole moments and hyperfine constants are calculated for the
$5d^9 6s^2 ^2 D_{3/2, 5/2}$ states in isoelectronic neutral Au. This yields a
new value of the nuclear quadrupole moment $Q$($^{197}$Au) = +0.587(29) b.

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The categories of this paper are: atom-ph
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The categories of this paper are: plasm-ph
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The categories of this paper are: econ
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The categories of this paper are: nucl-th
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The categories of this paper are: supr-con
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The categories of this paper are: q-bio
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The categories of this paper are: hep-th
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The categories of this paper are: cmp-lg
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The categories of this paper are: chao-dyn
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The categories of this paper are: astro-ph
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The categories of this paper are: adap-org
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The categories of this paper are: q-alg
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The categories of this paper are: acc-phys
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The categories of this paper are: hep-ex
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The categories of this paper are: hep-ph
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The categories of this paper are: math