Absorption coefficient change

If a compound dissociates in a solvent and one part of the pair has another absorption than the other (e.g., p-nitrophenol/p-nitrophenolate), the absorption coefficient changes with dilution. This should be taken into consideration when different dilutions of a compound are compared. The concentration of an aqueous protein solution can be estimated by reading the UV absorption. The aromatic amino acids (phenylalanine, tryptophan, tyrosine)... 

Equations (4), (5) and (s) were derived under the assumption that the absorption coefficient k remains constant during the exposure. It may thus be supposed that the derivation of relation between X and gel fraction content of the polymer, with the assumption that the absorption coefficient changes during irradiation may yield useful results. If the light absorption by polymer film is properly measured, the following formula may be derived ... 

The reactor model for the 2,4-D photolysis. The simplified kinetic expression represented by equation 6.69 has the same form as equation 6.73. However, during the 2,4-D photolysis the radiation absorption characteristics of the reacting medium change. This is a very distinct phenomenon because (i) the uranyl oxalate reaction is a photosensitized reaction and the radiation absorbing species is not consumed, and (ii) conversely, not only the 2,4-D absorption coefficient changes, but absorption by reaction products increases the total absorption coefficient above the initial value. This phenomenon produces an unavoidable coupling between the steady state radiation balance and the unsteady state mass balance. The total absorption coefficient can be obtained from equation 6.68. Then ... 

After this calibration step (the effective absorption coefficient is determined from a known wall thickness change and the corresponding variation of the optical film density) the evaluation of local wall thickness changes Aw (corresponding to De,o) from the nominal wall thickness w o , (corresponding to Dnom) can be done according to ... 

In an EXAFS experiment the measurable quantity is the absorption coefficient a of Equation (8.16). If Qq is the absorption coefficient in the absence of EXAFS, deduced from the steeply falling background shown in Figure 8.32, then x k), the fractional change of a due to EXAFS, is given by... 

Applications Involving Nonlinear Absorption Phenomena. Saturable absorption (hole-burning) is a change (typically a decrease) in absorption coefficient which is proportional to pump intensity. For a simple two level system, this can be expressed as... 

EXAFS is observed as a modulating change in the absorption coefficient caused by the ejected electron wave back-scattering from the surrounding atoms, resulting in interference between ejected and back-scattered waves. It is defined as ... 

The rate of heat conduction is further complicated by the effect of sunshine onto the outside. Solar radiation reaches the earth s surface at a maximum intensity of about 0.9 kW/ m. The amount of this absorbed by a plane surface will depend on the absorption coefficient and the angle at which the radiation strikes. The angle of the sun s rays to a surface (see Figure 26.1) is always changing, so this must be estimated on an hour-to-hour basis. Various methods of reaching an estimate of heat flow are used, and the sol-air temperature (see CIBSE Guide, A5) provides a simplification of the factors involved. This, also, is subject to time lag as the heat passes through the surface. 

Fig. 3-3. Attenuation and filtering of polychromatic x-rays by aluminum. Variation of effective wavelength with thickness. The effective wavelengths shown in tin figure correspond to the measured mass absorption coefficients. The change ir effective wavelength accounts for the deviations from the (dashed) straight lines The x-ray intensities used gave 210 /xamp through 0.0127-cm aluminum (curve A) 3200 /xamp through 0.381-cm aluminum (curve B). (Liebhafsky, Smith, Tanis, anc Winslow, Anal. Chem., 19, 861.)...

Since the mass absorption coefficient of hydrogen changes very little with wavelength, its value (0.435) may be taken from the literature. For carbon, 0.567, which was obtained from the measured kf for benzene by allowing for the absorption due to hydrogen, will serve. For chlorine, the rounded value na = 12 was chosen on the basis of the literature, which gives 11.6 at 0.71 A.13 With the numerical values inserted, Equation 3-8 becomes... 

Effective wavelengths have been included in Table 3-1 to show the changes that occur in this important variable when one gas is substituted for another. These wavelengths correspond to mass absorption coefficients calculated from Equation 3-14 and were obtained by interpolation from tabulated values of absorption coefficients for different wavelengths.15... 

The change in the absorption effect with chemical composition can be calculated in simple cases by properly adjusting a (Equation 7-5) to allow for the change in mass absorption coefficient. The mass absorption coefficient of the sample for a given wavelength is given by... 

Inspection of the table shows that the quotient a/Wj e is in fact nearly constant that I changes much less rapidly than W e] and that the critical depth has doubled when the highest oxide is reached. All three conditions are reflections of the (positive) absorption effect that occurs in this binary system when iron is replaced by oxygen, which has a lower mass absorption coefficient. 

Ferroelectric materials are capable of being polarized in the presence of an electric field. They may exhibit considerable anomalies in one or more of their physical properties, including piezoelectric and pyroelectric coefficients, dielectric constant, and optoelectronic constant. In the latter case, the transmission of light through the material is affected by the electric field, which produces changes in refractive index and optical absorption coefficient. Varying the applied field changes the phase modulation. 

The fact that the absorption spectrum of CdS changes when electrons are produced on it may be regarded as a non-linear optical effect, i.e. a dependence of the absorption coefficient on the light intensity. Other non-linear effects, which are caused... 

---