ИСТИНА

The chemical kinetics of oxygen atoms and ozone molecules were investigated in a fully- modulated DC discharge in pure oxygen gas in a borosilicate glass tube, using cavity ringdown spectroscopy (CRDS) of the optically forbidden O(3P2)-> O(1D2) absorption at 630nm. Measurements were made over a range of tube temperatures (10 and 50°C) gas pressures (0.5-4 Torr) and discharge current (10-40 mA). The discharge current was square- wave modulated (on for 0.2 seconds and off for 1 second), allowing the build-up to steady- state and the decay in the afterglow to be studied. The O atom density decays non- exponentially in the afterglow, indicating a surface loss probability dependent on incident active particle fluxes. The ozone density passes through a maximum a few 100ms into the afterglow, then decays slowly. An existing time-resolved self-consistent 1D radial model of O2 positive column discharges was upgraded to interpret the new results. The ozone behaviour in the afterglow can only be modelled by the inclusion of: 1) surface production of O3 from the reaction of O2 molecules with adsorbed O atoms, 2) reactions of vibrationally-excited ozone with O atoms and with O2(a1∆g) molecules, and 3) surface loss of ozone with a probability of around 10-5. The example of simulation results and the experimental data comparison is shown in figure 1. At 0.5 Torr, models with only gas- phase production of O3 strongly underestimate the observed ozone densities (whether or not vibrational kinetics is included). At higher pressure (4 Torr) the model without vibrational kinetics seriously overestimates the ozone concentration (by factor ~2.5), whether or not ozone surface processes are included.