Radiative lifetimes and quenching rate coefficients for directly excited rotational levels of OH (A 2Σ+,v′=0)

Abstract

A narrow bandwidth pulsed dye laser has been used to excite OH ${\mathrm{X\hspace{0.17em}}}^2{\Pi }_i$ radicals to the ${\mathrm{A\hspace{0.17em}}}^2{\Sigma }^{+}$ state by pumping in the (0,0) vibrational band around 308 nm. The radiative lifetimes of specific (K′,J′) rotational levels in $\text{v′ = 0}$ were measured at low pressures $\text{⩽1\hspace{0.17em}}\mathrm{mTorr}$ which gave a mean lifetime ${\tau }_0\text{=0.721±0.009\hspace{0.17em}μ}\mathrm{s}\text{\hspace{0.17em}(2σ).}$ Electronic quenching rate constants for important atmospheric species ${\mathrm{N}}_2,$ ${\mathrm{O}}_2,$ ${\mathrm{H}}_2\mathrm{O},$ and also for ${\mathrm{H}}_2$ were measured for a range of initially excited rotational levels. A strong dependence of this rate constant on the initially excited level was found for ${\mathrm{N}}_2,$ and less markedly for ${\mathrm{O}}_2,$ with the rate constant tending to increase for the lowest rotational levels $\text{K′⩽3.}$ The implications of these measurements of radiative and quenching rates for state selected rotational levels of OH A, $\text{v′=0}$ to the laser‐induced fluorescence detection of atmospheric OH are discussed.