The Manitoba II high resolution mass spectrometer has been used to det
ermine the mass difference Si-28(2) O-16-(ClCl)-Cl-35-Cl-37 to be 14 0
13.07 (70 muu. When this value is combined with existing precise value
s for the other atomic masses in the doublet, the atomic mass of Si-28
is found to be 27.976 926 88 (35) u.