Atom-molecule inelastic collision dynamics in open shell systems: O + NO and Cl + NO Thomas A. Stephenson Department of Chemistry and Biochemistry, Swarthmore College O + NO collisions have been identified as critical to an understanding of the radiative cooling of the upper atmosphere and as the source of deviations of quantum state population distributions for the local kinetic energy distribution in the thermosphere. O + NO collisions act to cool vibrationally excited NO molecules formed by high energy solar radiation, competing with NO relaxation via chemiluminescence. NO infrared chemiluminescence (110 km above the Earth’s surface) In our experiments, we produce O atoms by photolysis of either SO2 or N2O at 193 nm. These high velocity O atoms interact with supersonic expansion cooled NO to produce rotationally, vibrationally, and electronically (spin-orbit) excited NO, which we detect using ultraviolet laser-induced fluorescence. Laser-induced fluorescence excitation spectrum of jet-cooled NO