Electron excitation of neutral and ionic levels in Townsend discharges of argon at high E/N
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We have measured the emission coefficients of the 3p levels of ArI: 3p1, 3p5, 3p6, 3p7, 3p8, and 3p10. The data for the 3p5, 3p6, 3p7, 3p8 and 3p10 levels were converted to excitation coefficients by using quenching coefficients from the literature. Measurements were performed in the range of E/N between \(\) to above \(\) except for the 3p7 level where measurements were done only up to \(\). The data for the emission coefficients for Ar II levels include two 4p' levels with terms 2P 0 1/2 and 2F 0 7/2, and three 4p levels with terms 2P 0 1/2, 4P 0 5/2 and 2D 0 5/2. The measurements for the ionic levels were done for E/N above \(\) up to nearly \(\). The absolute values of the coefficients were obtained from the intensity of the light emitted at the anode in the parallel plate self-sustained Townsend argon discharges. For low E/N the apparent emission coefficients (i.e. the normalized spatial profile of emission) for both neutral and ionic levels increase exponentially in almost the entire discharge gap. At about \(\) the exponentially increasing signal was obtained only near the anode, while at \(\) the spatial dependence was flat throughout the electrode gap.
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