TEMPERATURE-DEPENDENCE OF THE COLLISIONAL REMOVAL OF O-2(A(3)SIGMA(-2AND N-2()(U), V=9) WITH O)

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 rang e 150 to 300 K. In a cooled flow cell, the output of a pulsed dye lase r excites the O-2 to the v = 9 level of the A(3) Sigma(u)(+) state, an d the output of a time-delayed second laser monitors the temporal evol ution of this level via a resonance-enhanced ionization. We find the t hermally 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 c ontrast, the N-2 cross section at 225 K is similar to 8% smaller and g radually increases to a value at 150 K that is similar to 60% larger t han the room temperature value. The difference between the temperature dependence of the O-2 and N-2 collision cross section implies that th e removal by oxygen becomes more important at the lower temperatures f ound in the mesosphere, but removal by N-2 still dominates.