Positive ion spectra in He-CO-O2-laser discharges

The ion spectra of He-CO-laser discharges with and without small addition of O
2
is presented. It is shown that upon addition of oxygen the dominant positive charge carriers in the discharge are O
2
⁺
ions. It is argued that the oxygen ion O
2
⁺
is populated in stage processes: the
a^{3}\Pi
state of CO relaxes to a metastable state of oxygen, which in turn is ionized by electrons.