Collisional quenching of high rotational levels in A 2Σ+ OH

Abstract

Collisional removal of the v′=0 level of the A 2Σ+ state of the OH radical has been studied as a function of rotational level N′ at room temperature. OH in high rotational levels of the X 2Πi state were created by 193 nm photolysis of HNO3 and excited to A 2Σ+ by a tunable dye laser. Time decays of fluorescence at varying pressures were measured. For O2 and H2, the quenching cross section σQ decreased with increasing N′ until N′∼10; for higher N′ it appears to remain approximately constant. Xe behaves the same way except that the decrease continues to N′=15. For Kr, σQ appears to decrease to within experimental error of zero at N′=10; and for N2 it was within error of zero above N′=10. These results have implications for laser-induced fluorescence atmospheric monitoring of OH and combustion temperature determinations, as well as a fundamental understanding of collisional quenching. Quenching of OH, N′∼1, by HNO3 was found to be 81±8 Å2.