Spatially resolved spectroscopic profiles of plasmoidal rf discharges

The intensities of prominent visible emissions from rf‐excited plasmoidal discharges consisting of gaseous oxygen, oxygen/nitrogen mixtures, nitrogen, oxygen/carbon monoxide mixtures, and carbon monoxide have been recorded. In each case the radial dependence of the luminous output from a spherically symmetric discharge was obtained by deconvolution of the spatially resolved intensity data. Only the emissions associated with transitions between the relatively long lived excited states of the ions, i.e., $({\mathrm{O}}_2^{+}\mathrm{)*}$ and (CO⁺)* revealed the anomaly known as the dark sheath in the discharge. Further, the dark sheath was only observed when oxygen was present in the discharge. These results are in agreement with the ``delayed‐emission'' theory proposed by Kregel and Miller which associates the dark sheath with relatively long lifetimes for the excited states of the ions as well as with a coincident region of high electric field (peculiar to electronegative gases such as oxygen). Discharge pressures ranged from 10⁻⁴ and 10⁻³ Torr and the frequency of the applied rf field was 27.120 MHz.