Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Electronic ground states of Fe$_2^+$ and Co$_2^+$ as determined by x-ray
  absorption and x-ray magnetic circular dichroism spectroscopy   The $^6\Pi$ electronic ground state of the Co$_2^+$ diatomic molecular cation
has been assigned experimentally by x-ray absorption and x-ray magnetic
circular dichroism spectroscopy in a cryogenic ion trap. Three candidates,
$^6\Phi$, $^8\Phi$, and $^8\Gamma$, for the electronic ground state of Fe$_2^+$
have been identified. These states carry sizable orbital angular momenta that
disagree with theoretical predictions from multireference configuration
interaction and density functional theory. Our results show that the ground
states of neutral and cationic diatomic molecules of $3d$ transition elements
cannot generally be assumed to be connected by a one-electron process.

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The categories of this paper are: dg-ga
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The categories of this paper are: adap-org
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The categories of this paper are: acc-phys
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The categories of this paper are: atom-ph
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The categories of this paper are: supr-con
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The categories of this paper are: chem-ph
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The categories of this paper are: eess
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The categories of this paper are: math-ph
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The categories of this paper are: astro-ph
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The categories of this paper are: math
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The categories of this paper are: cmp-lg
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The categories of this paper are: mtrl-th
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The categories of this paper are: hep-ex
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The categories of this paper are: patt-sol
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The categories of this paper are: econ
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The categories of this paper are: q-fin