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Absorption strength

Since the optical transitions near the HOMO-LUMO gap are symmetry-forbidden for electric dipole transitions, and their absorption strengths are consequently very low, study of the absorption edge in Ceo is difficult from both an experimental and theoretical standpoint. To add to this difficulty, Ceo is strongly photosensitive, so that unless measurements arc made under low light intensities, photo-induced chemical reactions take place, in some cases giving rise to irreversible structural changes and polymerization of the... [Pg.48]

The optical transition moments for vibrational or electronic transitions between defect states have specific orientations with respect to the defect coordinates. The absorption strength of polarized light for each of the differently oriented centers is proportional to the square of the component of the transition moment that is along the polarization direction. Hence, a stress-induced redistribution of the defects among their different orientations will be detected as an anisotropy in the polarized optical absorption. A convenient measure of the anisotropy is the dichroic ratio, defined as... [Pg.158]

There is a relationship between scattering strength and absorption strength, in that strong scatterers are also in principle strong absorbers. The parameters are often combined, as will be seen in Chapter 4, into a complex stracture factor in which the real part represents the scattering factor (equation (1.4)) and the imaginary part the absorption coefficient (equation (1.2)). [Pg.5]

Two final examples of the sensitivity and general applicability of the FTIR gas analysis technique are illustrated in Fig. 8. Trace (A) shows the spectrum obtained from an ultra-air filled 70 liter sampling bag into which had been injected, 18 hours previously, 4.8 microliters of TDI, toluene diisocyanate. On the basis of the single feature at 2273 cm l, it is estimated that 50 ppb TDI could be detected. The lower Trace (B), shows the spectrum of nickel carbonyl. This highly toxic but unstable gas was found to decay rapidly at ppm concentrations in ultra air (50% lifetime 15 minutes). Calibration of its spectrum was established by recording successive spectra at ten minute intervals and by attributing the increase in carbon monoxide concentration (calibration known) to an equivalent but four times slower decrease in nickel carbonyl concentration. The spectrum shown represents 0.6 ppm of the material. Note the extraordinary absorption strength. The detection limit is thus less than 10 ppb. [Pg.174]

At present, the quantitative data on absorption strengths etc. needed to fully evaluate this possibility are not available. [Pg.99]

Principle of corresponding states. The principle of corresponding states, originally introduced by van der Waals and applied since to model inter-molecular potentials, transport and equilibrium properties of fluids over a wide range of experimental conditions, was remarkably successful, albeit it is not exact in its original form. An interesting question is whether one could, perhaps, describe the diversity of spectral shapes illustrated above by some reduced profile, in terms of reduced variables. If all known rare-gas spectra are replotted in terms of reduced frequencies and absorption strengths,... [Pg.137]

The anisotropy parameter indicates that this is a parallel transition ( Qg - N) and the absorption coefficient suggests that it is much stronger than the corresponding CH Br transition. While the authors suggest that this is a mystery, it could be that the absorption strength is a result of the heavy I atom breaking down the spin selection rule. [Pg.69]

The increase in the radiative decay rate of 4F3/2 under pressure was estimated from the measured absorption strength of the 4l9/2 4F3/2 transitions and the relative luminescence... [Pg.573]

For increasing chain lengths, low frequency exciton components between 1630 and 1640 cm1, gain in intensity in the calculated absorption strengths. For the "spiral staircase" geometry, the computed VCD intensities of the low frequency exciton components cancel. [Pg.104]

The form of eq. (11) is similar to that encountered in CD spectroscopy. Finally, it should be noted that this equation has been derived for measurements at a particular wavelength, X expressions involving integrated (over the electronic band) rotatory and absorption strengths may also be developed [2],... [Pg.214]

Matrices produced had absorption spectra similar to that shown in Fig. 2 when fluorescence experiments were run. For raman experiments Mop absorption strengths of 2-3 OD were produced. The absorption spectra are perplexing in that peak shapes and spacings are widely varying. [Pg.220]

In the case of the alternant aromatic hydrocarbons, w, = w2 and a = b hence, the transition moment of the a band is zero. Since the oscillator strength is proportional to the square of the transition moment, the a band is forbidden, and its absorption intensity is very weak. For alternant aromatic nitrogen compounds, however, the values of w, and a are not equal to those of 2 and b, respectively hence, its transition moment does not vanish. Hence, the a band is allowed, and its absorption strength is stronger than that of the parent hydrocarbon. But it is still rather weak, because the value of a is near to that of b, and the transition moment (ML) is not so large. [Pg.324]

N-acetyltyrosinamide (green), and N-acetylphenylalaninamide (red) in aqueous solution. The absorption spectra (left) show the relative absorption strengths of the three amino adds. The fluorescence spectra (right) are normalized to the same peak intensity (see Table 1 for relative quantum yields), (b) Fluorescence emission spectra of the malelmide derivatives of four common fluorescent dyes Alexa Fluor 488 (green), tetramethyirhodamlne (yellow), Texas red (orange), and Cy 5 (red). [Pg.550]

The results for Eu " in CaF2 and SrF2 are even more interesting, since the excited 4/ levels cannot be observed by single-photon spectroscopy due to the overlap by the 4/ 5d band. At the same time, the lower position of the 4/ 5d states for Eu " relative to Gd increases the absolute two-photon absorption strength. [Pg.341]

The excitation mechanism of the anti-Stokes emission is as follows. First the ion is excited into the Dq level. Although the Fo- Do transition is highly forbidden (J = 0- J = 0), it has a rather high absorption strength in LaOCl due to the strong linear crystal-field component at the La CEu ) site. The lifetime of the Do level is long (of the order of milliseconds). A second photon is now absorbed, which raises the system to the charge-transfer state. This is an allowed transition. More-... [Pg.342]

The emission spectrum of [(jd " C 2.2.1] could only be obtained with high enough intensity under X-ray excitation (222). This is due to the weak absorption strength of the Gd lines. The analogous [Eu C 2.2.1] shows, under X-ray excitation, a considerable amount of [Eu C 2.2.1] emission (222). Since the formation of the divalent species under the applied s3uithesis conditions is very improbable, this [Eu C 2.2.1] emission shows that under X-ray excitation electrons are trapped at the europium ions. [Pg.390]

A recent example of this consideration is the success of [Eu C bpy.bpy.bpy] cryptate in luminescence immunoassay (104). This cryptate is used as a label to an antibody that is coupled in a specific way to a biomolecule, the presence of which has to be proved. TTie structure of the molecule is shown in Fig. 47. Excitation is into the bpy molecule, which shows a very high absorption strength in the ultraviolet part of the spectrum (cmax 10 M cm ). From the bpy triplet state the energy is transferred to the Eu ion, which finally emits (104,107). Although the quantum efficiency is only 1% (104), the high bpy absorption strength makes application feasible. [Pg.394]

In the gas phase, results on the photodissociation of ICN to yield I -F CN were recently reported [90,91]. Optical absorption of a 120-fs, 307-nm pulse produced an excited state that is unstable with respect to dissociation. The dynamics were probed by determining the time-resolved excited-state absorption strength (measured by laser-induced fluorescence) at various wavelengths. Data are shown in Figure 13. The appearance and decay of unstable intermediates along the dissociation pathway was noted. The clarity of this experiment lies in the simplicity of the sample, a small molecule in the gas phase. In conjunction with resonance Raman spectra [92, 93] and other results, these results may make possible a rather complete determination of dissociation dynamics and of the reactive potential surface. [Pg.28]

In a search of the spectral range from about 100 to 5000 cm", as well as in the near infrared and visible, we detected no other features. Based on the ratio of absorption strengths in the infrared lines to the infrared continuum one can estimate that the abundance of the Cto molecule is of the order of 1% of the total sample. [Pg.25]


See other pages where Absorption strength is mentioned: [Pg.310]    [Pg.389]    [Pg.195]    [Pg.356]    [Pg.359]    [Pg.74]    [Pg.773]    [Pg.232]    [Pg.276]    [Pg.341]    [Pg.89]    [Pg.132]    [Pg.71]    [Pg.77]    [Pg.177]    [Pg.126]    [Pg.30]    [Pg.213]    [Pg.143]    [Pg.130]    [Pg.339]    [Pg.382]    [Pg.6340]    [Pg.310]    [Pg.138]    [Pg.441]    [Pg.3381]    [Pg.105]    [Pg.369]   
See also in sourсe #XX -- [ Pg.141 , Pg.186 ]

See also in sourсe #XX -- [ Pg.549 ]




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