Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Investigations of Ra$^+$ properties to test possibilities of new optical
  frequency standards   The present work tests the suitability of the narrow transitions $7s \
^2S_{1/2} \to 6d ^2D_{3/2}$ and $7s ^2S_{1/2} \to 6d ^2D_{5/2}$ in Ra$^+$ for
optical frequency standard studies. Our calculations of the lifetimes of the
metastable $6d$ states using the relativistic coupled-cluster theory suggest
that they are sufficiently long for Ra$^+$ to be considered as a potential
candidate for an atomic clock. This is further corroborated by our studies of
the hyperfine interactions, dipole and quadrupole polarizabilities and
quadrupole moments of the appropriate states of this system.

23
The categories of this paper are: solv-int
12
The categories of this paper are: nucl-th
33
The categories of this paper are: plasm-ph
11
The categories of this paper are: hep-lat
26
The categories of this paper are: bayes-an
20
The categories of this paper are: acc-phys
0
The categories of this paper are: hep-ph
9
The categories of this paper are: nlin
16
The categories of this paper are: stat
17
The categories of this paper are: q-fin
14
The categories of this paper are: math-ph
34
The categories of this paper are: chem-ph
19
The categories of this paper are: eess
1
The categories of this paper are: cs
4
The categories of this paper are: cond-mat
24
The categories of this paper are: dg-ga