Shifts and Widths of Some Stark-Broadened Oxygen Lines in an Arc Plasma

Abstract

A thermal oxygen plasma was generated in a wall-stabilized arc and its temperature and electron density were determined spectroscopically from the intensity measurement of an oxygen line of known transition probability. Observations were made over the range of electron densities from (1 to 6)×${10}^{16}$ ${\mathrm{cm}}^{-3\mathrm{}}$ and for temperatures around 10 000°K. The profiles of several oxygen lines were scanned end on and side on, and the shifts and half-widths were compared with the results of a recently developed Stark-broadening theory for isolated lines of heavy elements. The agreement in the half-widths is very good, with deviations usually smaller than 10%. The ratio of measured to calculated width averaged over the six investigated multiplets is 1.00 with a standard deviation of ±0.06. However, the agreement in the shifts is good only in those cases where the shifts are large. For the two strongly broadened multiplets at 6046 and 6455 Å, detailed side-on observations were made at various radial distances. They show the theoretically expected linear dependence of half-widths and shifts on the electron density over the measured range. For the strong multiplet at 6455 Å the intensity distribution in the distant line wings was measured, too, and could be represented by power laws with exponents of -1.96 for the blue wing and -1.91 for the red wing, in close agreement with theoretical asymptotic formulas.