Electron impact excitation of argon in the extreme vacuum ultraviolet

Polarization-free excitation cross sections in the extreme vacuum ultraviolet have been measured for electron impact on Ar. Observed spectral features were those lines of ArI and ArII which lie between 700 and 1100 Å. Excitation functions were measured for the ArI resonance line at 1048 Å and the ArII resonance line at 920 Å. Peak cross sections for these two lines were found to be (39.4 ± 7.9) × ${10}^{-18\mathrm{}}$ and (6.9 ± 1.4) × ${10}^{-18\mathrm{}}$ ${\mathrm{cm}}^2$, respectively. At low energies, excitation of the ArII resonance line is dominated by an electron exchange transition.