The $Q$ value of the ${}^{112}\mathrm{Sn}$ double-beta decay was determined by using a Penning trap mass spectrometer. The new atomic-mass difference between ${}^{112}\mathrm{Sn}$ and ${}^{112}\mathrm{Cd}$ of 1919.82(16) keV is 25 times more precise than the previous value of 1919(4) keV. This result removes the possibility of enhanced resonance capture of the neutrinoless double-EC decay to the excited $0^{+}$ state at 1871.00(19) keV in ${}^{112}\mathrm{Cd}$.

• Received 17 March 2009

DOI:https://doi.org/10.1103/PhysRevLett.103.042501