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 X 2Πi radicals to the A 2Σ+ state by pumping in the (0,0) vibrational band around 308 nm. The radiative lifetimes of specific (K′,J′) rotational levels in v′ = 0 were measured at low pressures ⩽1 mTorr which gave a mean lifetime τ0=0.721±0.009 μs (2σ). Electronic quenching rate constants for important atmospheric species N2, O2, H2O, and also for H2 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 N2, and less markedly for O2, with the rate constant tending to increase for the lowest rotational levels K′⩽3. The implications of these measurements of radiative and quenching rates for state selected rotational levels of OH A, v′=0 to the laser-induced fluorescence detection of atmospheric OH are discussed.