Double-β-decay Q values of 74Se and 76Ge

The atomic masses of Ge-74, Se-74, Ge-76, and Se-76 have been determined from cyclotron frequency ratios of pairs of ions simultaneously trapped in a cryogenic Penning trap. Allowing for cancellation of systematic errors in the mass differences between isobars, we determine the Q value for double-electron capture of Se-74 to be 1209.240(7) keV, and the Q value for double-electron emission of Ge-76 to be 2039.061(7) keV. The new Q(2EC) value for Se-74 precludes a large resonant enhancement for neutrinoless double-electron capture.