Extinction efficiency values

The amount of fluorescence emitted by a fluorophore is determined by the efficiencies of absorption and emission of photons, processes that are described by the extinction coefficient and the quantum yield. The extinction coefficient (e/M-1 cm-1) is a measure of the probability for a fluorophore to absorb light. It is unique for every molecule under certain environmental conditions, and depends, among other factors, on the molecule cross section. In general, the bigger the 7c-system of the fluorophore, the greater is the probability that the photon hitting the fluorophore is absorbed. Common extinction coefficient values of fluorophores range from 25,000 to 200,000 M 1 cm-1 [4],... 

Sulfate Average Mass Extinction Efficiency, ct. Comparison of Statistically Inferred Values... 

For absorbing spheres, the curve for is usually of simpler form, rising rapidly to reach a maximum at small values ofx and then falling slowly to approach two at large values of A". Figure 5.3 shows the extinction efficiency for carbon spheres. For such particles, nearly... 

The extinction efficiency factor Q , approaches a constant asymptotic value of 2 with increasing size parameter. It means that a large particle attenuates (absorbs and scatters) twice as much energy from an incident beam as characterized by its own geometric area. The additional attenuation is because of diffraction of the EM waves by the particle. This phenomenon... 

Brewster and Kunitomo [231] attempted to obtain coal refractive indices with a different approach. Following an earlier work by Janzen [226], they suspended coal particles in a KBr matrix and measured spectral transmission from the samples. Assuming particles are spherical and knowing the size distribution and volume fraction of coal in the sample, they predicted the extinction efficiency factor Qt . Using a dispersion equation curve fitting for Qe , they determined the complex index of refraction of different coal samples. They reported values for the absorption index kK that was an order of magnitude smaller than earlier studies. 

The extinction efficiency of a water droplet as a function of the size parameter a is shown in Figure 15.3. We note that Qext approaches the limiting value 2 as the size parameter increases ... 

Optical transmission spectra of the films irradiated with H+ ions are shown in Figure 9.13a. A maximum transmittance of about 75% is observed for the as-deposited film whereas the transmittance is decreased for the ion-implanted samples. From the transmittance data, the refractive index and extinction co-efficient are evaluated. The index of refraction value of n=2 and the extinction co-efficient value of nearly k=0 in the visible region is obtained and these values are typical of most of the spinel transparent conducting oxide (TCO) materials. 

If we assume that the individual particles in an aggregate are large enough such that the extinction efficiency gext for these particles is not very sensitive to particle size, then the extinction caused by an aggregate will be proportional to the projected area of that aggregate. The value of the extinction coefficient approaches two as the particle size becomes large, but for many particles does not depart very far from this value once the condition... 

Samples of narrow polystyrene (PS) latex, steam-stripped to remove excess, unreacted monomer, were purchased from a supplier in order to test the calculation of extinction efficiencies for use in correcting data from a disc centrifuge photosedimentometer.l It was crucial that the sizes were known with an accuracy of 1%, independent of the DCP measurement. TEM values were given by the manufacturer. In addition PCS and DCP measurements were made. Table 1 shows the results. 

As shown in these figures, the extinction efficiency for large or highly absorptive particles approaches the value of 2. This is the Fraunhofer regime, where the total extinction is due to the redistribution of the incident light because of diffraction about the edge of the sphere, specular reflection at the... 

The solvent used was 5 %v/v ethyl acetate in n-hexane at a flow rate of 0.5 ml/min. Each solute was dissolved in the mobile phase at a concentration appropriate to its extinction coefficient. Each determination was carried out in triplicate and, if any individual measurement differed by more than 3% from either or both replicates, then further replicate samples were injected. All peaks were symmetrical (i.e., the asymmetry ratio was less than 1.1). The efficiency of each solute peak was taken as four times the square of the ratio of the retention time in seconds to the peak width in seconds measured at 0.6065 of the peak height. The diffusivities obtained for 69 different solutes are included with other physical and chromatographic properties in table 1. The diffusivity values are included here as they can be useful in many theoretical studies and there is a dearth of such data available in the literature (particularly for the type of solutes and solvents commonly used in LC separations). 

In this section we apply the adaptive boundary value solution procedure and the pseudo-arclength continuation method to a set of strained premixed hydrogen-air flames. Our goal is to predict accurately and efficiently the extinction behavior of these flames as a function of the strain rate and the equivalence ratio. Detailed transport and complex chemical kinetics are included in all of the calculations. The reaction mechanism for the hydrogen-air system is listed in Table... 

Note that the index of refraction of the continuous phase and that of the dispersed particles enter the evaluation of the various efficiencies. The light that actually strikes the particles is used in the determination of x- This light differs from that under vacuum by the refractive index of the medium. This effect enters the calculation of the x values in that it is the ratio of the refractive index of the particle relative to that of the medium that determines the extinction. 

The longest wave absorption band of anthracene is short axis polarized. The substitution in 9,10 positions leads to a bathochromic shift in this band. The intrinsic lifetimes are proportional to Jandean be obtained from the area under the respective absorption curves. The molar extinction coefficients are 9, 10-dichloro-A > 9-chloro-A > A. The lifetime decreases with increase of absorbance and at the same time the fluorescence efficiency f is observed to increase. The values of f f°r various anthracenes in CC14 and the quantum efficiencies of their reactions with the solvent, both in absence of oxygen, are presented in Table 11.5. 

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