Precise ground-state hyperfine splitting inii173

A laser-microwave double-resonance experiment on electrodynamically trapped $^{173}\mathrm{Yb}^{+}$ ions has been performed and a value of \ensuremath{\Delta}${\ensuremath{\nu}}_{\mathrm{h}\mathrm{f}\mathrm{s}=10\phantom{\rule{0ex}{0ex}}491\phantom{\rule{0ex}{0ex}}720239.55}$\ifmmode\pm\else\textpm\fi{}0.09 Hz for the ground-state hyperfine separation has been determined. This value is corrected for small Zeeman and second-order Doppler shifts. Combined with a previous similar measurement on $^{171}\mathrm{Yb}^{+}$ and with the known ${g}_{I}$ values of both isotopes, we obtain a value of -0.004 25(6) for the differential hyperfine anomaly $^{171}\mathrm{\ensuremath{\Delta}}^{173}$.