The K-beta transitions of Ar ions, excited in an electron beam ion trap, we
re detected with the help of an X-ray crystal spectrometer. The spectrum wa
s analyzed by using Hartree-Fock calculations with Cowan computer code. Hig
h-energy features above 3190 eV, belonging to the K-beta transitions in tra
pped Ar III and Ar IV ions, were observed in the spectrum. An unfitted maxi
mum at 3192 eV was interpreted as the result of 1s-3d excitation of inner s
hell electrons in Ar II ions.