Predissociation lifetimes of OH A 2Σ+ (v′=3) obtained from optical–optical double-resonance linewidth measurements

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Abstract
The excitation of rapidly predissociating v’=3 levels in the A 2Σ+ state of OH has recently been suggested as a means of avoiding collisional quenching corrections when performing laser‐induced fluorescence (LIF) measurements in flames. We report measurements of predissociation rates of several rotational levels in v’=3, obtained from linewidths in optical–optical double‐resonance (OODR) spectra. The magnitude of the observed predissociation rates places an upper limit on the pressures at which OH LIF can be considered ‘‘quench‐free.’’ In addition, analysis of spectral line shapes suggests that rotational transfer can significantly affect LIF quantum yields at pressures of 1 atm and higher. We conclude that variations of the predissociation rate with rotational level in v’=3 must be included in determinations of rotational temperatures from LIF.