Flame laser excitation spectra

Figure 3. Laser-excitation spectrum for nitric oxide in CHi-02-N2 flame at atmospheric pressure (spectrometer set for 0,1 y-band at 2368.8 A)...

The laser atomic fluorescence excitation and emission spectra of sodium in an air-acetylene flame are shown below. In the excitation spectrum, the laser (bandwidth = 0.03 nm) was scanned through various wavelengths while the detector monochromator (bandwidth = 1.6 nm) was held fixed near 589 nm. In the emission spectrum, the laser was fixed at 589.0 nm, and the detector monochromator wavelength was varied. Explain why the emission spectrum gives one broad band, whereas the excitation spectrum gives two sharp lines. How can the excitation linewidths be much narrower than the detector monochromator bandwidth ... 

Fluorescence excitation and emission spectra of the two sodium D lines in an air-acetylene flame, (a) In the excitation spectrum, the laser was scanned, (to) In the emission spectrum, the monochromator was scanned. The monochromator slit width was the same for both spectra. [From s. J. Weeks, H. Haraguchl, and J. D. Wlnefordner, Improvement of Detection Limits in Laser-Excited Atomic Fluorescence Flame Spectrometry," Anal. Chem. 1976t 50,360.]... 

Figure 19. The laser-induced fluorescence excitation spectrum of the Ct swan band system in an acetylene-air flame (21)...

Figure 13. Fluorescence spectrum for S02 and SO in a H2-02 N2 (3 1 5) flame with 1 % HsS added to the unburnt gas. Laser excitation at 266.5 nm.

Figure 15. Comparison of CH flame emission and laser-excited fluorescence spectrum in an oxy-acetylene slot torch...

Excitation by flame is less effective than by electric arc or spark, glow, or plasma discharge, or by lasers which produce a more line-rich spectrum on the other hand, these advantages can only be exploited by instruments capable of higher resolution. ... 

CARS can be resonantly-enhanced electronically when either the pump, Stokes or the CARS frequency Itself coincides with an electronic transition in the probed species. Stokes resonances are weighted by the excited vibrational state involved in the Raman resonance and this enhancement is generally weak even at flame temperatures. More typically one tries to achieve primary resonance with the pump laser. In so doing, Stokes resonances are automatically satisfied. The strength of the resonance scales as the product of the four dipole matrix elements Involved with each field in the wave mixing process. Thus only certain transitions tend to be enhanced leading in most cases to a simplification of the CARS spectrum. In the case of the combustion relevant OH molecule under study in our laboratory, a simple triplet spectrum is predicted since each Raman-resonant, downward Stokes transition must satisfy the appropriate dipole selection mles for strong electronic enhancement as shown in Fig. 10. ... 

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