STUDY OF ELECTRON-IMPACT EXCITATION OF ARGON IN THE EXTREME ULTRAVIOLET - EMISSION CROSS-SECTION OF RESONANCE LINES OF AR-I, AR-II

We 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 ArI at 104.8 nm and 106.7 nm and of ArII 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 ArI lines at 104.8 nm and 106.7 nm are 23.1 X 10-18 cm2 and 9.32 X 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 ArI resonance lines than previous emission experiments have indicated. In addition all the emission cross sections for the ArI, II Rydberg series in the EUV spectral interval are measured at 0.5 nm resolution. The far ultraviolet (FUV) spectrum of Ar is also surveyed for the first time and is found to consist of ArII multiplets from simultaneous ionization-excitation.