Flame fluorescence profile

Fluorescence profiles for SH in a rich H2/O2/N2 flame containing varying amounts of H2S are shown in Figure 12. The similarity with the profiles for S2 in Figure 8 suggests that S2 and SH are chemically coupled. 

Fluorescence profiles for SO in a rich flame with added H2S are presented in Figure 15. The corresponding profiles for S02 are shown in Figure 16. Similarity of the SO and S02 profiles suggest that they are chemically coupled. 

Figure 12. SH A2X — X2U fluorescence profiles above the burner surface for Hg-Ot-Nt (4 1 6) flames with added HtS (a),l. 0% (b), 0.5% (c), 0.25%. Laser excitation at 323.76 nm with detection at 328.0 nm.

Reaction (7) couples S2 and SH, as was noted from their fluorescence profiles. Similarly, reaction (12) links SO to S02. Reactions (13) and (14) connect oxidized and reduced species, SO with S2 and SH. The model relates all sulfur bearing species in the flames. The non-equilibrium concentrations of H and OH radicals generated in the flame front by the fast radical chain branching reactions... 

The hydroxyl concentration profile for a stoichiometric CH -air flame is presented in Figure 8. Here the maximum mole fraction observed and the predicted mole fraction are equal to better than 10% accuracy. The abscissas of the theoretical and the experimental results were matched by setting the theoretically predicted temperature equal to the measured hydroxyl rotational temperature. At all positions in the flame the hydroxyl 2j[(v,=o) state exhibited a Boltzmann distribution of rotational states. This rotational temperature is equal to the N2 vibrational temperature to within the +100 K precision of the laser induced fluorescence and laser Raman scattering experiments. An example of this comparison is given in Figure 9. 

The measurements of temperature and species concentrations profiles in premixed, laminar flames play a key role in the development of detailed models of hydrocarbon combustion. Systematic comparisons are given here between a recent laminar methane-air flame model and laser measurements of temperature and species concentrations. These results are obtained by both laser Raman spectroscopy and laser fluorescence. These laser probes provide nonintrusive measurements of combustion species for combustion processes that require high spatial resolution. The measurements reported here demonstrate that the comparison between a model and the measured concentrations of CH, O2,... 

Concentration Profiles. The relative fluorescence intensity profiles for OH, S2, SH, SO, and SO2 were converted to absolute number densities according to the method already outlined. Resulting concentration profiles for a rich, sulfur bearing flame are exhibited in Figure 17. H-atom densities were calculated from the measured OH concentrations and H2 and H2O equilibrium values for each flame according to Equation 6. Similar balanced radical reactions were used to calculate H2S and S concentrations 6). Although sulfur was added as H2S to this hydrogen rich flame, the dominant sulfur product at early times in the post flame gas is S02 ... 

Saturation Broadening in Flames and Plasmas As Obtained by Fluorescence Excitation Profiles... 

Gaussian Laser Profile-Voigt Atom Profile. This case turns out to be a better approximation of our experimental situation, i.e., the laser FWHM is fairly broad compared to the absorption line width and the absorption profile of atoms in an atmospheric combustion flame is described by a Voigt profile. Here the laser is assumed to have a Gaussian spectral profile as well as a Gaussian atomic absorption profile. In this case, convolution of two Gaussian functions is still a Gaussian function. Evaluation of the ratio n2/nT, and the fluorescence radiance. Bp, allows determination of the half width of the fluorescence excitation profile, 6X... 

COMPARISON BETWEEN THE THEORETICAL AND THE EXPERIMENTAL VALUES OF THE FLUORESCENCE EXCITATION PROFILE HALFWIDTHS FOR THE Ar/02/H2 FLAMES.(a) ... 

Determination of Flame and Plasma Temperatures and Density Profiles by Means of Laser-Excited Fluorescence... 

A flame profile provides useful informalir>n ahoiil the processes lhai go on in different parts of a flame it is a contour plol lhal reveals regions of the flame lhal have similar values for a variable of interest. Some t>f these variables include icinperaiurc. chemical composition, absorbance, and radiant or fluorescence iniensiiv. 

FIGURE 11-3. Relation of height above burner head to relative intensity of the fluorescence signal Cadmium atomic fluorescence intensity profiles in premixed and unpremixed nitrous oxide—hydrogen flames, (a) Atomic fluorescence in optimized N2O/H2 premixed flame, (d) Atomic fluorescence in optimized N2O/H2 unpremixed flame, (c) Scatter in N2O/H2 premixed flame, (cf) Scatter in N2O/H2 unpremixed flame. [From M. P. Bratzel, Jr., R. M. Dagnall, and J. D. Winefordner, Evaluation of Premixed Flames Produced Using a Total Consumption Nebulizer Burner in Atomic Fluorescence Spectrometry, Anal. Chem., 41,1527 (1969). Used by permission of the American Chemical Society.]... 

The decay trace shown in the upper part of Fig. 4 is obtained following laser excitation of a specific N level in the v =0 level of the state of CH in the burner. Here, the spectrometer which viewed the fluorescence was tuned to 390 nm, the location of the (0,0) band of the B-X system. If the spectrometer wavelength is changed to 413 nm, the trace in the lower panel results. This is fluorescence in the (0,0) and (1,1) bands of the A-X system, produced by CH molecules which have been coUisionally transferred from the B to the A state. Note that the risetime of the A-X emission is the same as the decay of the B-X trace, whereas the A state dies out more slowly, having smaller gq for all flame conditions and the three individual collision partners for which measurements were made. Spatial profiles showing the fluorescence from A caused by collisional transfer fiom B are given in Figs. 2 and 3. 

Spatial variations in the temperature and concentration of atomic iron in a low-pressure lean (cp = 0.37) H2/02/Ar/Fe(C0)s flame were measured using laser-induced fluorescence (Wlokas et al., 2009 Staude et al., 2009a). Iron pentacarbonyl was foxmd to decompose in the flame to produce atomic iron, which was then transformed to iron oxides and hydroxides. On the basis of a previously developed mechanism (Rumminger et al., 1999), a reduced 12-step mechanism for flame inhibition by Fe(CO)s was developed and validated by comparing measured and simulated concentration profiles of atomic iron. 

Pulsed flame photometric detector, provides two simultaneous signals for S and P by measurement of a fluorescence/time profile in the range of 2—25 ms with about 5 Hz cycle time (after Prof. Aviv Amirav, University Tel Aviv, Israel). 

Parameters discussed previously for line broadening in emission spectrometry are also applicable for fluorescence spectrometry, especially since many of the same atom producers (flames, inductively coupled plasmas, etc.) are used for both techniques. In fluo rescence, the width of the absorption profile can be... 

Food and feed quality begins with the selection of the best-quality ingredients, which are evaluated in terms of physical properties that include color, smell, taste, and texture, and proximate and chemical analyses that include amino acids, fatty acids, minerals, and vitamins. The amino acid profile is usually determined by ion-exchange chromatography or HPLC systems equipped with fluorescent detectors. The fatty acid composition is, in most instances, analyzed via gas chromatography coupled with a flame ionization detector. New capillary columns allow the analysis of fatty acid isomers, such as trans configured, that need to be declared in food labels in many countries around the globe. 

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