ON THE RELATIONSHIP BETWEEN THE POPULATION OF THE FINE-STRUCTURE LEVELS OF THE GROUND ELECTRONIC-STATE OF ATOMIC OXYGEN AND THE TRANSLATIONAL TEMPERATURE

Using a recent calculation of the cross sections for fine structure ch anging collisions during an encounter between two oxygen atoms in the ground electronic state, we determine the population of the fine struc ture levels of oxygen as & function of altitude for four model atmosph eres representing conditions at 0-degrees longitude, 45-degrees latitu de, at midday and midnight, and high and low solar and geomagnetic act ivity. We include the effect of electron impacts. The fine structure l evels are shown to be in local thermodynamic equilibrium (LTE) at die local neutral atom translational temperature for altitudes up to 350 k m and 400 km for midnight and midday, respectively, at low activity, a nd up to at least 600 km at high activity. At higher altitudes spontan eous emission causes deviation from LTE and overpopulates the lowest ( J=2) level at die expense of the other two levels.