Photochemical effects in 205-nm, two-photon-excited fluorescence detection of atomic hydrogen in flames

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Abstract
This Letter describes photochemical effects observed by using 205-nm, two-photon-excited fluorescence spectroscopy to measure the atomic-hydrogen concentration in atmospheric-pressure hydrogen–oxygen flames. We found that the 205-nm radiation photolyzed water produced in the flame, forming atomic hydrogen in concentrations higher than those naturally present in lean flames and leading to erroneous concentration measurements. UV excitation of molecular oxygen transitions near 205 nm is also discussed; such excitation, followed by rapid predissociation to produce atomic oxygen, may also affect some flame measurements.