Band emission spectra

Contributions from band emission spectra, especially in the region of intensive band systems (CN at 370-385 nm, Nj" at 390-400 nm, NH at 340-350 nm, OH at 310-320 nm). Also here weighted corrections, as in the case of matrix line wings may be necessary. 

A more common type of spectral interference in either emission or absorption measurements arises from the occurrence of band emission-spectra due to molecular species in the flame. (In fact, many elements can be measured by means of the band spectra of the molecules they form in certain flames.) Calcium and strontium, for example, exist partially as molecular hydroxides and oxides in a flame and emit bands in the vicinity of both the sodium and lithium resonance lines. When the alkaline-earth/alkali-metal ratio is high, the interference can become serious, unless a high-resolution monochromator is used. 

In the work on TiC and related compounds discussed above the structure of valence band emission spectra is not discussed. In several instances, however, it appears that lines originating in the valence bonding region can give information on the order and constitution of bonding molecular orbitals. This has been discussed in some detail by Urchd i) for compounds of second short period elements and by Fischer - for 3d transition element compounds. 

Previously, attempts were made to model the middle IR band emission spectra (2 to 5.5 i,m) from the rocket fuel chemistry and the physical properties during combustion by making use of techniques such as quantum mechanics and computational fluid dynamics. These methods proved to be too time consuming and the accuracies of the predictions were not acceptable (Roodt, 1998). 

Diphenylphosphinoethyl-functionalised imidazolium salts and their silver-carbene complexes were used to synthesise a series of di- and trinuclear gold complexes able to exhibit multi-band emission spectra. The PL properties of these species are likely significantly influenced by gold-gold interactions. ... 

Figure 141 shows the EL spectra from a microcavity (a) and conventional LED (b) based on the emission from an NSD dye forming a thin emitting layer of a three-organic layer device. It is apparent that the half-width of emission spectra from the diode with microcavity is much narrower than those from the diode without cavity. With 0 = 0°, for example, the half-width of the spectrum of the diode with cavity is 24 nm whereas that of the sample without cavity increases to 65 nm. According to Eq. (275), the resonance wavelength, A, decreases with an increase of 0 in agreement with the experimental data of Fig. 141. We note that no unique resonance condition in the planar microcavity is given due to broad-band emission spectrum of the NSD emission layer. Multiple matching of cavity modes with emission wavelengths occurs. Thus, a band emission is observed instead a sharp emission pattern from the microcavity structure as would appear when observed with a monochromator the total polychromic emission pattern is a superposition of a range of monochromatic emission patterns. The EL spectra...

More careful work on the nature of the products of the electrical discharge passed through SO2 and S has forced the re-evaluation of these conclusions on the H2S oxidation. Meschi and Myers found that the major product in such a system was not S2O2, as had been believed, but S2O, and that this was the species responsible for the banded emission spectrum observed by Markovich and Emanuel and by Norrish and Zeelenberg. In the discharge system, such a product might be formed by direct combination ... 

The vibrational structure of a resonance Raman spectrum is thus similar to that of a (hot-band) emission spectrum. This relationship between Raman spectra and their REPs is equivalent to the mirror-image relationship observed between absorption and emission spectra in simple cases (Mingardi et ai, 1975). 

Germanium monofluoride, GeF, is known only from the band emission spectrum from a discharge in Gep4. The bond force constant of the molecule is calculated to be 3.92 x 10 dynes/cm27. 

Description of Method. Quinine is an alkaloid used in treating malaria (it also is found in tonic water). It is a strongly fluorescent compound in dilute solutions of H2SO4 (f = 0.55). The excitation spectrum of quinine shows two absorption bands at 250 nm and 350 nm, and the emission spectrum shows a single emission band at 450 nm. Quinine is rapidly excreted from the body in urine and is easily determined by fluorescence following its extraction from the urine sample. 

A quick analysis of Equation (77) shows that if the melt layer is thin (kd 1), the emission spectrum corresponds to an absorption spectrum. This means that the emission peaks occur at the same wave numbers as the absorption bands. In case of thick melt layers (kd 1) Equation (77) becomes the following expression ... 

Opposite behavior was displayed by molten fluoride systems. For instance, no bands were observed in the thin layer emission spectrum of a KF - K2SiF6 melt, whereas increasing the melt layer to 10-20 mm led to the appearance of two intensive bands at 730 and 476 cm 1. These bands correspond to v3 and v4 vibrations of the complex ion SiF62 Solid K2SiF6 is characterized by IR absorption bands at 741 and 483 cm 1 [343]. 

The emission spectrum observed by high resolution spectroscopy for the A - X vibrational bands [4] has been very well reproduced theoretically for several low-lying vibrational quantum numbers and the spectrum for the A - A n vibrational bands has been theoretically derived for low vibrational quantum numbers to be subjected to further experimental analysis [8]. Related Franck-Condon factors for the latter and former transition bands [8] have also been derived and compared favourably with semi-empirical calculations [25] performed for the former transition bands. Pure rotational, vibrationm and rovibrational transitions appear to be the largest for the X ground state followed by those... 

Additional support for this disassembly mechanism was obtained by monitoring the release of the pyrene tail units by fluorescence spectroscopy. The confined proximity of the pyrene units in the dendritic molecule results in formation of excimers. The excimer fluorescence generates a broad band at a wavelength of 470 nm in the emission spectrum of dendron 31 (Fig. 5.25). Upon the release of the pyrene units from the dendritic platform, the 470 nm band disappeared from... 

Absorption and Emission Spectra. The excitation-emission spectrum of 1 (bottom half of Fig. 1) shows that the relatively narrow emission band is nearly independent of the excitation wavelength and that the excitation spectrum is not only nearly independent of the wavelength at which the emission is monitored, but is also very similar to the absorption spectrum, both being somewhat broader than the emission band. This leaves no doubt that the observed emission is due to the polysilane, and its shape, location and the mirror image relation to the absorption permit its assignment as fluorescence. 

Figure 6.1. Jablonski-type diagram for pyrazine. The zero-field splittings (between tx, tV) t2) are not drawn to scale. Spin polarization ( x x x) resulting from the most probable intersystem crossing routes and part of the emission spectrum where different vibronic bands (v = /,/, k) have different zf origins are schematically indicated. (After El-Sayed.(17))...

On the other hand, the exposed copolymer yarn containing 4.0 mole percent 4,4 -BPDC still exhibits the normal terephthalate fluorescence (388 nm emission) as the major band in the emission spectrum when excited with 342 nm energy. 

For recording the intensity ratio at two emission wavelengths, it should possess strongly different emission spectrum but a comparable intensity to that of reporter band. 

A study of the valence band photoelectron spectrum and the X-ray emission spectrum of poly(ethylene oxide) was carried out by Brena and co-workers [102] in order to understand the effect of conformation on the observed spectra. Up to 12 monomers were used in the calculations for the valence band photoelectron... 

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