ИСТИНА

The number density of O2 (b1Σ+) molecules in the positive column of a dc discharge in pure O2 was determined by high-resolution vacuum ultraviolet (VUV) absorption of the (4pπ1Σ+u ← b1Σ+) band at 131.3nm (using the Fourier Transform Spectrometer at the DESIRS beamline at Synchrotron Soleil) and from the absolute intensity of the A-band (b1Σ+v=0→3Σ − g ,v=0) emission at 760nm. The 131.3nm absorption band is the only one that is well separated from O2 X and a absorption bands. An analysis of the rotational structure of this heavily-perturbed band is presented as well as an ab − initio calculation of the (previously-unknown) transition strength. The densities obtained by the two methods agree within 20%, confirming the accuracy of the transition strength calculation. The O2 b density increases with O2 pressure up 2 Torr (reaching about 1 % of the total gas density), then decreases at higher pressure. At low pressure the b density increases with discharge current, whereas the opposite trend is observed at high pressure. These observations can be explained by O2 b quenching by O 3P atoms with a rate that increases with temperature.