Emission spatial profiles

Previous evidence for the mechanism of formation of CH comes from two experiments. A measurement [6] of spatial profiles in low-pressure C2H2/O2 flames showed the ratio [CH ]/[C2][OH] to be remarkably constant with variation in many different flame parameters. Only the A A state was observed, however. In a more recent study [7] in a low pressure discharge flow at room temperature, emission spatial profiles, measured downstream from mixing of 0 + C2H2, were compared with the results of a computer calculation, varying many discharge parameters. Here it was concluded that CH was produced from the reaction O + C2H, not the reaction C2 + OH deduced from the flame study. The present profiles suggest that neither mechanism is solely responsible for the formation of electronically excited CH. 

However, as we noted earlier (in Section II), it is most important to have a full temporal and spatial profile of the picosecond laser pulses in order to correctly interpret the one or two photon excited molecular response functions (absorption, emission, Raman scattering) of the system under study. While autocorrelation techniques such as second harmonic generation (SHG) or two photon fluorescence have always been the route to such short pulse measurements, a significant advance has recently been made in bringing these conventional autocorrelation measurements into the real-time domain. ... 

The main building blocks of any LIF set-up incorporate (i) the laser system, (ii) the reaction environment, and (iii) the fluorescence detection system. In addition, various ancillary groups might be encountered, such as optical components to shape the incoming laser beam, and most likely some imaging optics for efficient collection of the fluorescence emission. Also, some laser monitoring equipment is likely, measuring the laser s power, and temporal, spectral and spatial profiles. 

Fig. 2 shows the spatial profiles for a stoichiometric propane/oxygen flame at 6.5 Torr. There are several salient features. First, the OH emission profile peaks higher off the burner (i.e., later in the flow) than the ground state CH profile. The O2 concentration, although not measured here, must continually decrease as a function of distance from the burner. Over this region, the temperature (measured... 

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. 

A general picture of the effect of concomitant on analyte ion emission in the ICP is shown in the spatial profiles in fig. 11. Sodium is chosen as a typical concomitant. Addition of sodium enhances the analyte intensity low in the plasma, whereas a slight suppression is observed higher in the normal analytical... 

The Physical Electronics 680 Nanoprobe employs a field emission electron gun, and this results in a spatial resolution of less than lOnm. Ion bombardment for depth profiling is available in the SAM, and both the electron beam and the ion beam are computer controlled so that depth profiles can be run automatically, and maps and line scan of Auger electron distributions can be generated. 

It has been shown recently [25] that concentrations of NOj, tend to reduce with increase in the amplitude of discrete-frequency oscillations. The mechanisms remain uncertain, but may be associated with the imposition of a near-sine wave on a skewed Gaussian distribution with consequent reduction in the residence time at the adiabatic flame temperature. Profiles of NO, concentrations in the exit plane of the burner are shown in Fig. 19.6 as a function of the amplitude of oscillations with active control used to regulate the amplitude of pressure oscillations. At an overall equivalence ratio of 0.7, the reduction in the antinodal RMS pressure fluctuation by 12 dB, from around 4 kPa to 1 kPa by the oscillation of fuel in the pilot stream, led to an increase of around 5% in the spatial mean value of NO, compared with a difference of the order of 20% with control by the oscillation of the pressure field in the experiments of [25]. The smaller net increase in NO, emissions in the present flow may be attributed to an increase in NOj due to the reduction in pressure fluctuations that is partly offset by a decrease in NOj, due to the oscillation of fuel on either side of stoichiometry at the centre of the duct. 

I /I )2 should be an increasing function of L. One has to keep in mind that due to a two-dimensional orientational distribution function of the in-plane molecular alignment, the contribution of / normalized to the total intensity / +ij, a=/ /(/ +/j ) differs from one even for a homogeneously oriented device, as for example a = 0.75 with S — 3. It is clear that the experimentally observed EL anisotropy plotted against the distance, x, from the A1 cathode (located at x = 0), and identified with varying thickness (L) of parallel oriented n monolayers, contains the EL emission profile determined by the spatial distribution of emitting states, x(x) ... 

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