Collisional quenching of high rotational levels in A (2)Sigma(+) OH

Collisional removal of the v'=0 level of the A (2)Sigma (+) state of the OH radical has been studied as a function of rotational level N' at room temp erature. OH in high rotational levels of the X (2)Pi (i) state were created by 193 nm photolysis of HNO3 and excited to A (2)Sigma (+) by a tunable dy e laser. Time decays of fluorescence at varying pressures were measured. Fo r O-2 and H-2, the quenching cross section sigma (Q) decreased with increas ing N' until N'similar to 10; for higher N' it appears to remain approximat ely constant. Xe behaves the same way except that the decrease continues to N'=15. For Kr, sigma (Q) appears to decrease to within experimental error of zero at N'=10; and for N-2 it was within error of zero above N'=10. Thes e results have implications for laser-induced fluorescence atmospheric moni toring of OH and combustion temperature determinations, as well as a fundam ental understanding of collisional quenching. Quenching of OH, N'similar to 1, by HNO3 was found to be 81 +/-8 Angstrom (2). (C) 2001 American Institut e of Physics.