Collisional Quenching of No A2sigma+(nu'= 0) Between 125 and 294 (Postprint)

We report measurements of the temperature-dependent cross sections for the quenching of fluorescence from the A 2Sigmav 0 state of NO for temperatures between 125 and 294 K. Thermally averaged cross sections were measured for quenching by NO X 2Pi, N2, O2, and CO in a cryogenically cooled gas flow cell. Picosecond laser-induced fluorescence was time resolved, and the thermally averaged quenching cross sections were determined from the dependence of the fluorescence decay rate on the quencher-gas pressure. These measurements extend to lower temperature the range of previously published results for NO and O2 and constitute the first reported measurements of the N2 and CO cross sections for temperatures below 294 K. Between 125 and 294 K, a negative temperature dependence is observed for quenching by NO, O2, and CO, implicating collision-complex formation in all three cases. Over the same temperature range, a constant, nonzero cross section is measured for quenching by N2. Updated empirical models for the temperature dependence of the cross sections between 125 and 4500 K are recommended.