PREDISSOCIATION LIFETIMES OF OH A2-SIGMA+ (V'=3) OBTAINED FROM OPTICAL OPTICAL DOUBLE-RESONANCE LINEWIDTH MEASUREMENTS

The excitation of rapidly predissociating upsilon' = 3 levels in the A2-SIGMA+ 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 upsilon' = 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 upsilon' = 3 must be included in determinations of rotational temperatures from LIF.