We have observed splittings between the &sgr;+and &sgr;−groups of components of optical lines emitted by fast beams of Ar+and O+[v/c= (3.2−4.2) × 10−3] in a magnetic field of 13 800 G. In order to observe these separations, which were of the order of 0.2–0.3 Å, it was necessary to reduce the recorded widths of spectral lines by refocusing the spectrometer and by exciting the beam in a gas target.