Abstract
Because of the importance of the hydroxyl radical (OH) as an intermediate in combustion processes, research on OH diagnostic tech- niques has been widespread. Andresen, et al.1 have recently shown that excitation of lines in the weak OH A2∑+ ←X2∏ (3,0) band using a powerful (400 mJ/pulse) KrF excimer laser results in strong laser-induced fluorescence (LIF). The A2∑+ state of OH is known to predissociate, especially in its higher vibrational levels, but the natural lifetime of many levels above v′ = 2 are not known accurately. The fluorescence quantum yield from the rapidly predissociating v′ = 3 state is insensitive to slower intermolecular processes such as coilisional quenching, presumably leading to improved measurement accuracy. However, the actual predissociation rate, which is required to calíbrate the quantum yield for concentration measurements, remains uncertain. Moreover, calculations indícate that the predissociation rate is expected to increase in higher rotational levels,2 leading to a potentially strong effect on temperature measurements.
© 1991 Optical Society of America
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