Measurement of CH2O in low and atmospheric pressure flames by Laser Induced Fluorescence and Cavity RingDown absorption

We have investigated the spatial structure of formaldehyde usinglaser-induced fluorescence (LIF), LIF imaging, and cavity ringdownspectroscopy (CRDS) in two flames. The first is an atmospheric pressureBunsen flame, into which are inserted various metal to simulatedifferent types of heat removal inserts in appliance flames. Here LIFimaging is used. The second is a low pressure flat flame that can bemodeled with a one-dimensional code. All three techniques are used. Theresults in both cases show that CH2O appears prior to CH, inlower pressure regions of the flame

Combustion Research Program: Flame studies, laser diagnostics, and chemical kinetics

We have made a detailed study of the care that must be taken to correctly measure OH radical concentrations in flames. A large part of these studies has concerned collisional quenching of hydride radical species (OH, NH, and NH{sub 2}), in particular the dependence upon rotational level and collision velocity (temperature). The results on OH and NH have shown unique and interesting behavior from the viewpoint of fundamental molecular dynamics, pointing to quenching often governed by collisions on an anisotropic, attractive surface, whereas NH{sub 2} quenching appears to depend on state-mixing considerations, not dynamic control. This state-specific behavior of these small, theoretically tractable hydrides has direct ramifications for quantitative flame diagnostics. Our other effort in the diagnostic area has been repeated but unsuccessful searches for laser induced fluorescence in the vinyl radical

Collisional processes near the CH B 2Σ- v′=0,1 predissociation limit in laser-induced fluorescence flame diagnostics

Excitation and dispersed laser-induced fluorescence spectra of CH¿B¿2S-v'=0,1 in methane flames are analyzed using rotational relaxation models to investigate their applicability for flame diagnostics. The existence of non-predissociative and highly predissociative rotational levels in the same vibrational state provides a unique scenario to test the effects of rotational relaxation in laser-induced fluorescence measurements. Using a statistical power gap law for rotational relaxation modeling, we find that the levels with collision-free lifetimes as short as 100 ps have apparent fluorescence yields larger than expected because of the extent of rotational relaxation at atmospheric pressure. Also, vibrational (v'=1 to v'=0) and electronic energy transfer (B¿2S-v'=1 to A¿2¿) are competitive, and together are half the value for the total collisional removal rate from CH¿B¿2S-v'=0. The measured electronic energy transfer branching ratio into A¿(v'=0-3) depends on the initial rotational level pumped, and energy gap considerations can be used to explain these propensities. The combination of measurements and model calculations finds the excitation of the CH¿B¿2S-¿v'=1,N'=8 level a good candidate for laser-induced fluorescence quantitative measurements in flames at atmospheric pressure

Collisional processes near the CH B 2Σ- v′=0,1 predissociation limit in laser-induced fluorescence flame diagnostics

Excitation and dispersed laser-induced fluorescence spectra of CH¿B¿2S-v'=0,1 in methane flames are analyzed using rotational relaxation models to investigate their applicability for flame diagnostics. The existence of non-predissociative and highly predissociative rotational levels in the same vibrational state provides a unique scenario to test the effects of rotational relaxation in laser-induced fluorescence measurements. Using a statistical power gap law for rotational relaxation modeling, we find that the levels with collision-free lifetimes as short as 100 ps have apparent fluorescence yields larger than expected because of the extent of rotational relaxation at atmospheric pressure. Also, vibrational (v'=1 to v'=0) and electronic energy transfer (B¿2S-v'=1 to A¿2¿) are competitive, and together are half the value for the total collisional removal rate from CH¿B¿2S-v'=0. The measured electronic energy transfer branching ratio into A¿(v'=0-3) depends on the initial rotational level pumped, and energy gap considerations can be used to explain these propensities. The combination of measurements and model calculations finds the excitation of the CH¿B¿2S-¿v'=1,N'=8 level a good candidate for laser-induced fluorescence quantitative measurements in flames at atmospheric pressure