Mass and double-beta-decay Q value of 136Xe

The atomic mass of Xe-136 has been measured by comparing cyclotron frequencies of single ions in a Penning trap. The result, with 1 standard deviation uncertainty, is M(Xe-136) = 135.907 214 484 (11) u. Combined with previous results for the mass of Ba-136 [Audi, Wapstra, and Thibault, Nucl. Phys. A 729, 337 (2003)], this gives a Q value (M[Xe-136] - M[Ba-136])c(2) = 2457.83(37) keV, sufficiently precise for ongoing searches for the neutrinoless double-beta decay of Xe-136.