Emission spectroscopy of an Ar-O-2 dc magnetron sputtering plasma has been performed at 3.5 cm above a Ti target. The behavior of O-2(+) and O have been studied by introducing O-2 into the Ar plasma. The vibrational distributions of O-2(+) (b) radiative state have been determined. It is found to exhibit a quasi-Boltzmann distribution with vibrational temperatures between 2500 and 3500 K for discharge current between 200 and 500 mA at 5 mTorr. By comparing intensities of O and O-2(+) by emission spectroscopy and O-2(+) relative density by mass spectroscopy, the O/O-2 relative dissociation rate is found to be followed by the I-O/IO2+ optical intensity ratio. It is found to have an increase of n(O)/n(O2) with the discharge current. (C) 2002 Elsevier Science B.V. All rights reserved.