Laser-induced fluorescence detection of singlet CH2 in low-pressure methane/oxygen flames |
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Authors: | Andrew D. Sappey David R. Crosley Richard A. Copeland |
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Affiliation: | (1) Molecular Physics Laboratory, SRI International, 94025 Menlo Park, CA, USA;(2) Present address: Los Alamos National Laboratory, GP-CLS-3 M5-J565, Box 1663, 87545 Los Alamos, NM, USA |
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Abstract: | Methylene, CH2, is a chemically important intermediate in hydrocarbon combustion but has previously eluded optical detection in a combustion environment. The CH2 signal as a function of height above the burner surface in a premixed, laminar, methane/oxygen flame (5.6 Torr and fuel equivalence ratio 1.05) is measured by laser-induced fluorescence (LIF) in theB1 – ã1A1 electronic system. The ã state which lies 3165 cm–1 above the ground state is populated at the high temperatures of the flame (800–1800 K). Although less than one photon for each laser pulse is detected, we can unambiguously attribute the LIF features in the region 450 to 650 nm to CH2 by both scanning the excitation laser and dispersing fluorescence. LIF temperatures and CH and OH LIF concentration profiles are also obtained for the flame. The CH2 radical concentration maximum occurs closer to the burner than that of either OH or CH, as expected from models of methane combustion chemistry. |
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Keywords: | 33.20.Kf 35.80.+s 82.40.Py |
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