Study of electron impact excitation of argon in the extreme ultraviolet: emission cross section of resonance lines of Ar I, Ar II

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Abstract
The authors have studied in a crossed-beam experiment under optically thin conditions the extreme ultraviolet (EUV) spectrum of argon produced by electron impact excitation. The most prominent features of the EUV spectrum between 40 and 110 nm are the resonance lines of Ar I at 104.8 nm and 106.7 nm and of Ar II at 91.96 nm and 93.21 nm. Absolute cross sections of these lines at 200 eV are measured by the relative-flow technique and compared with previous estimates. The measured emission cross section values at 200 eV for the Ar I lines at 104.8 nm and 106.7 nm are 23.1*10-18 cm2 and 9.32*10-18 cm2, respectively, with an uncertainty of 14%. When compared with electron energy loss estimates of the direct excitation cross section these values establish that cascading is larger for the Ar I resonance lines than previous emission experiments have indicated. The far ultraviolet (FUV) spectrum of Ar is also surveyed for the first time and is found to consist of Ar II multiplets from simultaneous ionization-excitation.