Recent modifications to the “Manitoba II” high resolution mass spectrometer are described. Mass differences among the members of the triplet ${}^{199}\mathrm{Hg}{-}^{183}{\mathrm{W}}^{16}\mathrm{O}{-}^{12}{\mathrm{C}}_2^{35}{\mathrm{Cl}}_5$ have been measured. These self-consistent mass differences give masses for ${}^{183}\mathrm{W}$ and ${}^{199}\mathrm{Hg},$ as well as the mass difference across the W to Hg region of the mass table. These masses and the mass difference provide important constraints for the least squares atomic mass evaluation.

• Received 22 January 2003

DOI:https://doi.org/10.1103/PhysRevC.67.064316