of ytterbium-173 by a combined theoretical and experimental investigation of the hyperfine level splittings in the first excited state ($4f^{13}(^2\!F^{o})6s^2$, $J=7/2$) of the $^{173}\mathrm{Yb}^{+}$ ion. This ${}^2\!F^o_{7/2}$ state is metastable, contains six $m_F=0$ states that will be first-order insensitive to magnetic fields, and easily state-selectively coupled to the ground state for precision spectroscopy.

  -------------------------------------- ------------------- ----------------------------- ------------------- ----------- ---------
    $^{87}\mathrm{Rb}$ [@Gerginov2009]    $\frac{3}{2}^{-}$   $p_{3/2}, \mathrm{proton}$    $^2\!P_{{3}/{2}}$      $-0.58$    $0.30$
     $^{113}\mathrm{In}$ [@EckKus57]      $\frac{9}{2}^{+}$   $g_{9/2}, \mathrm{proton}$      $^2\!P_{3/2}$        $0.574$    $0.99$
     $^{115}\mathrm{In}$ [@EckKus57]      $\frac{9}{2}^{+}$   $g_{9/2}, \mathrm{proton}$     $^2\!P_{{3/2}}$       $0.565$    $1.00$
    $^{133}\mathrm{Cs}$ [@GerDerTan03]    $\frac{7}{2}^{+}$   $g_{7/2}, \mathrm{proton}$    $^{2}\!P_{{3/2}}$       $0.82$   $0.022$
   $^{137}\mathrm{Ba^{+}}$ [@Lewty2013]   $\frac{3}{2}^{+}$   $d_{3/2}, \mathrm{neutron}$   $^{2}\!D_{{3/2}}$    $-0.0629$   $0.039$
   $^{155}\mathrm{Gd}$ [@Unsworth1969]    $\frac{3}{2}^{-}$   $p_{3/2}, \mathrm{neutron}$       $^9\!D_3$          $-1.66$   $-0.29$
    $^{165}\mathrm{Ho}$ [@DanFerGeb74]    $\frac{7}{2}^{-}$   $f_{7/2}, \mathrm{proton}$    $^4\!I_{{15/2}}$        $0.75$     $1.0$
       $^{173}\mathrm{Yb}$ [@Singh]       $\frac{5}{2}^{-}$   $f_{5/2}, \mathrm{neutron}$      $^{3}\!P_2$         $-34.4$    $0.15$
  -------------------------------------- ------------------- ----------------------------- ------------------- ----------- ---------

  :  Compilation of spectroscopic determinations of nuclear octupole moments. $\Omega^\mathrm{emp}$ are the empirical moments derived from the combination of spectroscopic HFS measurements and electronic structure calculations. $\Omega^\mathrm{SP}$ are octupole moments predicted by the single-particle model [@sch55]. All octupole moments are in units $\mathrm{barn}\times \text{nuclear magneton} (\mathrm{b\times{\mu_N}})$. All listed isotopes are stable except for $^{115}\mathrm{In}$ and $^{87}\mathrm{Rb}$ with half-lives of $4.4\times10^{14}$ and $4\times10^{10}$ years, respectively [@Stone2005]. Values of $\Omega$ have also been 