Q values for neutrinoless double-electron capture in 96Ru, 162Er, and 168Yb

The $Q$ values of the neutrinoless double-electron capture transitions in ${}^{96}\text{Ru}$, ${}^{162}\text{Er}$, and ${}^{168}\text{Yb}$ have been determined by Penning-trap mass-ratio measurements. Based on our new high-precision results for the $Q$ values, neither of these transitions shows a resonant enhancement of the capture rate. At present, this excludes these nuclides from the list of suitable candidates in the search for neutrinoless double-electron capture.