Precise atomic mass differences for wide doublets as determined with the Manitoba II mass spectrometer

In work reported previously, the 1 m radius, second-order, double-focusing mass spectrometer at the University of Manitoba ('Manitoba II') has been used to determine the spacing, ΔM, of relatively narrow mass spectral doublets (1/115 000 < ΔM/M < 1/17 000). In this work, involving relatively much wider doublets, we describe a systematic correction which must be applied to such determinations. We also report new values for the 37Cl – 35Cl mass difference and for two rare earth doublets which check the reliability of a large body of previous data.