Auger Line Shapes of Free Atoms

Quantitative calculations of Auger line shapes of free atoms after particle-impact ionization are presented. It is shown that the line shapes deviate from Lorentzians for all impact energies, due to long-range continuum interactions between the Auger electron and unobserved collision fragments. In particular, even at asymptotically high impact energies, the observed linewidth ${\Gamma }_{\mathrm{FWHM}}$ exceeds the decay width ${\Gamma }_0$ of the initial state by up to 10%; moreover, the line shapes are slightly, but noticeably shifted and asymmetrically distorted with respect to a Lorentzian. The magnitude of these effects was unknown in the past; possible implications for various subfields of physics are discussed.