ИСТИНА

Despite many decades of study, models of discharges in molecular gases still lack accurate data on many key collisional processes, even for such “simple” and ubiquitous gases as O2. Good data is lacking for near-threshold electron-impact dissociation, surface recombination, the role of metastable molecules and atoms, of gas heating, of vibrational excitation, of energy transfer processes, and surface thermal accommodation. Ideally, the rate constants of these processes would be individually measured in dedicated experiments, but this is fastidious, if it is even possible. As an alternative approach, we compare comprehensive measurements of internal plasma parameters to simulations for a plasma with relatively simple chemistry, namely a DC positive column discharge in pure O2. This wellcharacterized, stable and uniform discharge is optimal for experiment-model comparison. The excellent axial uniformity (uniform reduced electric field) is ideally suited to absorption spectroscopy techniques, which provide accurate absolute densities. Although oxygen plasmas have been studied for many years, new experimental methods, including synchrotron Vacuum UltraViolet (VUV) absorption spectroscopy and laser cavity ringdown absorption spectroscopy (CRDS), provide the densities of all the major species (atomic, molecular, in ground and excited states) with much-improved absolute accuracy. Furthermore, time-resolved measurements in (fully and partially) modulated discharges and with time resolution, allow the kinetics of reactive species to be probed. The high spectral resolution of CRDS also allows the gas translational temperature to be …