Flame luminescence

Crider WL, Slater RW Jr. 1969. Flame-luminescence intensification and quenching detector (FLIQD) in gas chromatography. Anal Chem 41 531-533. 

Spectroscopy of Flames Luminescence Spectra of Reactive Intermediates 182... 

Temp and relative intensities of the combustion products detected as a function of height along an RDX flame are shown in Fig 8 (Ref 67d). Intense radiation from the OH radical is observed immediately next to the combustion surface of the RDX sample. The intensity of the radiation attains its max value at a distance of 0.1mm and varies slowly with further increase in height along the flame. Luminescence of the radicals C2, CN, and CH appears at a distance of 0.1—0.2mm from the combustion surface and increases markedly as the zone of max temp in the flame is approached... 

Scattered light collected by the FI.5 lens (f = 30 cm) is relayed to the photomultiplier tube via 1 mm slits, a 1 nm bandwidth interference filter and a polarization filter, to reduce background from flame luminescence. The PDP-11/34 computer instructs the A/D convertor to make a conversion every 100 vsec. The resulting digital data are stored sequentially in core memory. The memory is saturated at 16,000 temperature measurements, at which time the data are transferred to a hard disk memory. The data in this transfer constitute one time... 

Wider application of the Rayleigh scattering technique for temperature or concentration measurements will, to some extent, rest on the ability to overcome two problem areas flame luminescence and Mie scattering from particles. Neither problem appears insurmountable. 

At certain positions in the flame, the background flame luminescence received by the photomultiplier tube can be 15% of the Rayleigh scattered intensity. A large reduction of this noise would be achieved by replacing the 1 nm bandpass filter with a monochrometer. Use of a multipass cell (12) or intracavity laser (13) would raise the signal above the flame luminescence. In addition, the increased scattered photon count rate would increase the precision of each measurement. 

The blue luminescence observed during cool flames is said to arise from electronically excited formaldehyde (60,69). The high energy required indicates radical— radical reactions are producing hot molecules. Quantum yields appear to be very low (10 to 10 ) (81). Cool flames never deposit carbon, in contrast to hot flames which emit much more intense, yellowish light and may deposit carbon (82). 

The majoiity of the various analyte measurements made in automated clinical chemistry analyzers involve optical techniques such as absorbance, reflectance, luminescence, and turbidimetric and nephelometric detection means. Some of these ate illustrated in Figure 3. The measurement of electrolytes such as sodium and potassium have generally been accomphshed by flame photometry or ion-selective electrode sensors (qv). However, the development of chromogenic ionophores permits these measurements to be done by absorbance photometry also. 

Excited states may be formed by (1) light absorption (photolysis) (2) direct excitation by the impact of charged particles (3) ion neutralization (4) dissociation from ionized or superexcited states and (5) energy transfer. Some of these have been alluded to in Sect. 3.2. Other mechanisms include thermal processes (flames) and chemical reaction (chemiluminescence). It is instructive to consider some of the processes generating excited states and their inverses. Figure 4.3 illustrates this following Brocklehurst (1970) luminescence (l— 2)... 

Many flames show perceptible spectra produced by chemo-luminescence, such as the diatomic molecules CH, C2 and CN in the blue-green cone of a Bunsen burner (7) also known from the absorption spectra of sun-spots and of red stars, and from the emission (probably fluorescence) of comet tails. 

Europium also does not modify the mantle thermoluminescence perceptibly. There are no sharp emission lines in the red due to a conceivable luminescence of a quasi-stationary concentration of Uo built up by the flame, in contradistinction to cathodo-luminescence. It must be remembered that the Boltzmann population of this state is only 4.10 even at 2000 K. 

Thus, although the colour of sparks is dependent upon flame temperature and may be similar to that of black body radiation, the overall colour effect can include contributions from atomic line emissions, from metals (seen in the UV and visible regions of the electromagnetic spectrum), from band emissions from excited oxide molecules (seen in the UV, visible and IR regions) and from continuum hot body radiation and other luminescence effects. So far as black body radiation is concerned, the colour is known to change from red (500 °C glowing cooker... 

Detonation (and Explosion), Flame (or Light) in. See Detonation (and Explosion), Luminosity (or Luminescence) Produced on... 

Effect of turbulence on flame radiation) (Authors measured the radiation intensity from propane flames and found a decrease in radiation with turbulence. Radiation is not thermal, but appears to be a luminescent phenomenon) 11) T.E. Holland et al, JApplPhys 28, 1217(1957)... 

Luminous Phenomena. See Detonation (and Explosion) Luminosity (Luminescence) Produced on, in Encycl 4 (1969), D425-L to D434-L Flash and Flame in Encycl 6 (1974), F74-R to F75-L, and Fluorescence, Luminescence and Phosphorescence, F124-R to F125-L Addl d Refs 1) A. Michel-Ldvy H. Muraour, CR 206, 1566-8 (1938) CA 32, 5629 (1938) (Luminosity of expls) 2) H. Muraour, A. Michel-Levy J. Rouvillois, CR 208,... 

W. D. Bancroft and H. B. Weiser point out that the blue luminescence of sodium is obtained without the yellow luminescence (i) when sodium salts are introduced into a flame of hydrogen in chlorine (ii) when metallic sodium bums slowly in oxygen, chlorine, or bromine (iii) when a sodium salt is fused (iv) when cathode rays act on sodium chloride (v) when anode rays first act on sodium chloride (vi) when one heats the coloured residue obtained by the action of anode rays or cathode rays on sodium chloride and (vii) when sodium chloride is precipitated rapidly from aq. soln. with hydrochloric acid or alcohol. The yellow luminescence of sodium is obtained, accompanied by the fainter blue luminescence (i) when a sodium salt is introduced into the Bunsen flame (ii) when sodium burns rapidly in oxygen, chlorine, or bromine and (iii) when canal rays act on sodium chloride. It is claimed that the yellow luminescence is obtained when sodium vapour is heated but it is very difficult to be certain that no burning takes place under these conditions. 

Above 250°C. we approach, in the gas phase, what is known as the cool flame regime. This is characterized by induction periods and by the appearance of pressure peaks and luminescent phenomena in the oxygen-hydrocarbon system. The consensus of present data seems to support the contention that these cool flames arise from the secondary decomposition of the hydroperoxides produced by the low temperature chain. The unimolecular decomposition of the hydroperoxide yields active alkoxy and hydroxyl radicals ... 

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