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Absolute differential cross sections have been measured for the ejection of electrons of various energies at 160° by argon ions and protons striking argon gas as a target. The observed energy spectrum consists of a number of "lines" or peaks superimposed on a continuous spectrum. The fine-structure regions occur below 20 eV and from about 120 to 220 eV for both projectiles. A number of lines are identified with auto-ionization transitions from neutral states and with Auger transitions from one- and two-vacancy states. With argon ions each peak has a "Doppler"-shifted counterpart due to electrons emitted from the moving particles. The data are compared with the Fano-Lichten electron-promotion model and with the statistical theories of Russek and of Everhart and Kessel.