Temperature dependence of the collisional removal of O-2(A(3)Sigma(+)(u), v=9) with O-2 and N-2

The temperature dependence of the collisional removal of O-2 molecules in the upsilon = 9 level of the A(3) Sigma(u)(+) electronic state has been studied for the colliders O-2 and N-2, over the temperature range 150 to 300 K. In a cooled flow cell, the output of a pulsed dye laser excites the O-2 to the v = 9 level of the A(3) Sigma(u)(+) state, and the output of a time-delayed second laser monitors the temporal evolution of this level via a resonance-enhanced ionization. We find the thermally averaged removal cross section for O-2 collisions is constant (similar to 10 Angstrom(2)) between room temperature and 200 K, then increases rapidly with decreasing temperature, doubling by 150 K. In contrast, the N-2 cross section at 225 K is similar to 8% smaller and gradually increases to a value at 150 K that is similar to 60% larger than the room temperature value. The difference between the temperature dependence of the O-2 and N-2 collision cross section implies that the removal by oxygen becomes more important at the lower temperatures found in the mesosphere, but removal by N-2 still dominates.