ON THE USE OF ACTINOMETRY TO MEASURE THE DISSOCIATION IN O-2 DC GLOW-DISCHARGES - DETERMINATION OF THE WALL RECOMBINATION PROBABILITY

A study has been performed to re-investigate the actinometric techniqu e used to determine the absolute concentration of O atoms in DC O-2 fl owing glow discharges for pressures ranging from 0.36 to 2 Torr and di scharge currents ranging from 5 to 80 mA in Pyrex tubes of three diffe rent diameters (16, 7 and 4 mm). Actinometric measurements using O(P-3 - S-3) 844 nm, O(P-5 - S-5) 777 nm and Ar(2p(1) - 1s(2)) 750 nm trans itions are compared to VUV absorption spectrometry. The choice of the excitation cross sections for the calculations of atomic excitation ra tes as a function of the reduced electric field using a Boltzmann code and the contribution of the quenching processes of the excited states are discussed. The dissociation ratio [O]/[O-2] can be determined fro m the ratio of intensities I-B44/I-750 by the relation [O]/[O-2] = C-3 p(2p1) I-844/I-750 We have found that C-3p(2p1) remains constant (C-3P (2p1) = 2.6 x 10(-3)) throughout the range of experimental conditions investigated. The recombination probability gamma of the O atoms at th e wail is calculated and correlated to the wall temperature of the Pyr ex tubes. The variation of the recombination probability as a function of the wall temperature is fitted by the relation gamma = 0.94 exp(-1 780/T-wall) for 300 < T-wall < 500 K.