Emission spectrum banding series

The emission spectrum consists of a series of weak bands starting at about 220 nm and then growing into a continuum from about 240 to 400 nm, with a maximum at approximately 270 nm as shown in Figure 5. Halstead and Thrush estimated that =65% of the emission occurs from the B2 state, =15% from the 3B3, and =20% from a combination of the A2 and Bi states [24, 28, 29] with a rate constant of 2 X 1CT31 cm6 molec 2 s 1 using argon as the bath gas at 300 K [53], As with the reaction of SO + 03 discussed above, collisional coupling results in a radiative lifetime that is pressure dependent. 

The chemiluminescent emission spectrum of GeCl2 was obtained by burning GeCl4 in potassium vapor using a diffusion flame technique 11 The spectrum consisted of a series of closely spaced diffuse bands in the region 4900—4100 A with an underlying continuum. The bands resemble those of SnCl2. 

A fine spectrum is an absorption or emission spectrum that displays a series of vertical fines indicating that only certain narrow wavelength bands (fines) are absorbed or emitted. A fine spectrum results when atoms are measured. This is the case because there are no vibrational levels in atoms, and therefore only very few transitions are allowed. 

The a3 n state of CO was first identified through its ultraviolet emission spectrum to the ground state, producing what are now known as the Cameron bands [160, 161, 162], Its radioffequency spectrum was then described by Klemperer and his colleagues in a classic series of molecular beam electric resonance experiments. Its microwave rotational spectrum was measured by Saykally, Dixon, Anderson, Szanto and Woods [163], and the far-infrared laser magnetic resonance spectrum was recorded by Saykally, Evenson, Comben and Brown [164], In the infrared region both electronic... 

Fig. 15. Rotatory artifacts that simulate Cotton effects at an absorption band. The dependence of the rotatory artifact on absorbance of p-cresol solutions placed in series with the same poly-L-glutamic acid solution is shown. The concentration of p-cresol was adjusted to give the total absorbance of chromophore plus polypeptide background that appears with each curve. The rotator, poly-L-glutamic acid, was at concentration of 0.5% at pH 7.0 in a 10-cm cell. The rotations are those actually observed, a, in degrees. The rotatory dispersion at Am 2 coincides almost exactly with that for the polypeptide alone, so that it has been omitted from the figure. At Am 4, an interference filter, /, with maximum transmission between 280 and 285 m/i, was placed in the optical path. The absorption spectrum, in arbitrary units, is typical of p-cresol plus poly-L-glutamic acid background. The emission spectrum is represented in arbitrary units, uncorrected for detector response. (Urnes et al., 1961a.)...

Intramolecular Excimer Fluorescence Studies in Polymers Carrying Aromatic Side Chains. Some years ago, it was shown that certain excited aromatic molecules may form a complex with a similar molecule in the ground state, which is characterized by a structureless emission band red-shifted relative to the emission spectrum of the monomer. The formation of such complexes, called "exclmers", requires the two chromophores to lie almost parallel to one another at a distance not exceeding about 3.5A° (11). Later, it was found that Intramolecular excimer formation is also possible. In a series of compounds of the type C5H (CH2)jiC H5, excimer fluorescence, with a maximum at 340nm, was observed only for n 3 -all the other compounds had emission spectra similar to toluene, with a maximum at about 280nm (12). Similar behavior was observed in polystyrene solutions, where the phenyl groups are also separated from one another by three carbon atoms (13). 

Figure 12 shows the emission spectrum at 4.2 K of a NaF-U (50 ppm) single crystal grown in air. The lines at 547.2 nm, 551.5 nm and 563.6 nm constitute the main lines of three line series corresponding with Runcimans A, B and C series ). Also a line series with main line at 540.8 nm is found. Each line series consists of a pattern of narrow lines and relatively broadened bands. 

The UVV emission spectrum of arylacetylide complexes 111 and 112 (item C-2 of Table 3) shows a vibrionic structure in which the series of Av = 2080-1880 cm-1 can be ascribed to superimposition of v(C=C) stretching vibrations206. The v(C=C) band at 1948-1912 cm-1 in the IR spectra of the titanocene complexes 172 pointed to the n-bonding of acetylenic moieties with Ag(I)241. See also Sections IV.D.2 and IV.F.2 below, and the analogous compound 116 (item C-5 of Table 3). 

Flame photometric detector FPD, a selective GC detector for sulphur and phosphorus containing compounds. Separated components pass into a hydrogen-rich flame where they undergo a series of reactions to produce excited species HPO and S2. The resulting atomic emission spectrum is monitored using narrow band pass filters (526 and 394 nm, respectively) and a photomultiplier detector, sensitivity is 10 to 10 " gs . ... 

The molecular model of the previous section can move as a whole, rotate about its center of mass, and vibrate. The translational motion does not ordinarily give rise to radiation. Classically, this follows because acceleration of charges is required for radiation. The rotational motion causes practically observable radiation if, and only if, the molecule has an electric (dipole) moment. The vibrational motions of the atoms within the molecule may also be associated nuth radiation if these motions alter the electric moment. A diatomic molecule has only one fundameiita] frequency of vibration so that if it has an electric moment its infrared emission spectrum will consist of a series of bands, the lowest of which in frequency corresponds to the distribution of rotational fre-c)uciicies for nonvibrating molecules. The other bands arise from combined rotation and vibration their centers correspond to the fundamental vibration frequency and its overtones. A polyatomic molecule has more than one fundamental frequency of vibration so that its spectrum is correspondingly richer. 

The SrCl molecule emits a series of bands in the 620- to 680-nanometer region, the deep red portion of the visible spectrum. Other peaks are also observed. Strontium monohydroxide, SrOH, is another substantial emitter in the red and orange-red regions. The emission spectrum of a red flare is shown in Figure 8.1. 

The lanthanide ions, particularly those near the middle of the series, samarium, europium, terbium, and dysprosium, form complexes that often emit visible radiation when excited in the near-ultraviolet. This emission spectrum can be analyzed by essentially the same procedure as for the absorption spectrum except that the nature of the emission process will generally yield additional information concerning the ground multiplet of the ion. The technique can be applied to solutions and solids but in solution various processes operate to reduce the intensity of the emitted light and to broaden the bands which can result in a reduction of the amount of information that can be obtained. 

Band emissions, on the other hand, are characteristic of excited molecules and a molecule, like an atom, can exist in a number of electronic energy levels. The change from one particular level to another results from the absorption or emission of a definite i.e. quantised) amount of energy. But, because of simultaneous changes which occur in the rotational or vibrational energy of the molecule, a series of closely spaced lines appear in the spectrum in the form of a band. 

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