Radial density distribution of excited atoms in a surface-wave-produced Ar-O2plasma column

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Abstract
The radial density distribution of Ar I and O I excited atoms in a radiative state and Ar(3P2) metastable atoms in an Ar-O2 cylindrical plasma column produced by an electromagnetic surface wave is examined experimentally. The radial density distributions of the Ar(3P2) metastable atoms and that of the O I radiative atoms are nearly flat, whereas the radial variation of Ar I radiative atoms can have a deep minimum on the plasma column axis. The difference in radial profiles leads to the conclusion that the atomic number density in the O(33P) level is the result of a two-step process, viz. dissociation of the O2 molecule and excitation of the ground-state atomic oxygen, this process being caused by Ar(3P2) metastable atoms (rather than by electrons) successively colliding with O2 and O. The results in Ar-OI2 are compared with observations made in Ne-O2.