[en] High energy resolution $\mathrm{K}{\mathrm{\beta <!--\; ??\; -->}}_{1,3}$ x-ray emission spectra of Ar induced in collisions with 0.75–3.0 MeV protons were measured using a complete in-vacuum curved-crystal x-ray emission spectrometer in Johansson geometry. The $\mathrm{K}{\mathrm{\beta <!--\; ??\; -->}}_{1,3}{\mathrm{M}}^{1,2}$ satellite lines were clearly resolved in the measured spectra and their intensity relative to the parent $\mathrm{K}{\mathrm{\beta <!--\; ??\; -->}}_{1,3}$ diagram line was used to extract the M shell single ionization probability for near-central collisions. The experimental values are compared to the theoretical predictions calculated within the semiclassical approximation (SCA) and also the binary encounter based geometrical model. Very good agreement with experimental data was achieved for the SCA values employing concise Dirac–Hartree–Fock wave functions for the description of valence M shell electrons. (paper)