A wall-stabilized high-current (100 A) arc was operated in argon at a pressure of 1 atm. Different gases (CO2, O2) could be added to the plasma. Temperature, electron, ion, and atom densities have been determined by spectroscopic observations in the visible and in the vacuum-ultraviolet (vuv) regions of the spectrum, assuming local thermal equilibrium. These values, together with the absolute emission intensities in the vuv region between 980 and 1250 Å, allowed the calculation of the photoionization cross section of carbon. This experimental value compared well with previously published theoretical calculations: it was 19×10-18 cm2 at threshold.
WALTER HOFMANN and GERHARD L. WEISSLER, "Measurement of the Photoionization Cross Section in the Resonance Continuum of C I Using a Wall-Stabilized Arc," J. Opt. Soc. Am. 61, 223-230 (1971)