Total cross sections forL-shell Auger-electron production and vacancy production in slow Si-Ar collisions

Total cross sections for Si $L$ and Ar $L$ Auger-electron production were measured in collisions of 35-500-keV ${\mathrm{Si}}^{+}$ ions incident on Ar atoms, and absolute cross sections for $L$-shell vacancy production were deduced. The experimental results are discussed in terms of the molecular-orbital model of atomic collisions. It is found that electron promotion via the $4f\sigma$ molecular orbital is the dominant mechanism for Si $L$-shell vacancy production. Excitation of $3d\pi$ and $3d\sigma$ electrons via $3d\delta -3d\pi -3d\sigma$ rotational coupling at small internuclear distances is treated explicitly. The calculated cross section for $3d\sigma$ excitation is found to reproduce the experimental cross section for Ar $L$-shell excitation in the range of collision energies up to 200 keV. $L-L$ vacancy-sharing processes at large internuclear distances are discussed as possible mechanisms for the observed rise of the Ar $L$ cross section beyond this energy.