Absorption coefficient due

Many of the trivalent lanthanide ions exhibit long-lived excited states. These excited states cannot be populated directly, since the lanthanide(III) ions themselves have very low absorption coefficients, due to the fact that the f-f transitions are formally forbidden by the LaPorte rule. In addition, a number of transitions are also forbidden by the spin crossover rule. Typically, these extinction coefficients are of the order of 1 M-1 cm-1 (20). 

They have large absorption coefficients due to allowed tt-tt transitions. 

Figs. 32a-c illustrate the absorption spectra, calculated, respectively, for water H20 at 27°C, water H20 at 22.2°C, and water D20 at 22.2°C dotted lines show the contribution to the absorption coefficient due to vibrations of nonrigid dipoles. The latter contribution is found from the expression which follows from Eqs. (242) and (255). The experimental data [42, 51] are shown by squares. The dash-and-dotted line in Fig. 32b represents the result of calculations from the empirical formula by Liebe et al. [17] (given also in Section IV.G.2) for the complex permittivity of H20 at 27°C comprising double Debye-double Lorentz frequency dependences. 

The contribution to the X-ray absorption coefficient due to the excitation of a deep core level may be expressed as /rc = nco-c, where nc is the density of atoms with the core level of concern and absorption cross section for this level on a single atom. Assuming the X-ray field to be a small perturbation, the latter can be evaluated from the golden rule transition rate per unit photon flux. The general X-ray absorption cross section is given by... 

The total absorption coefficient fx is given approximately by the sum of the partial absorption coefficients due to the photoeffect (/ ph), the Compton effect ( c) and pair formation ( p) ... 

The photoluminescent response is also used to study weak absorption coefficients due, for instance, to impurity states in the band gap of semiconductors, and it thus complements absorption measmements. 

The most important of these are the temperature dependence of the molar absorption coefficient (due to density change) the effect of association... 

Since 1970 the main anomalies in the propagation of ultrasonic waves in non-oriented samples of liquid crystals have been discovered these are the phase velocity dispersion and the nonclassical (a/f = constant) behavior of the ultrasound absorption coefficient due to the relaxation phenomenon. The anomalies are manifested in the megahertz Irequency range and are most pronounced in the vicinity of phase transitions. Kapustin [14] was the first to begin extensive investigations on the anomalies, and look at all types of liquid crystals. Most of the work done since 1980 has involved the use of a dc magnetic or electric field to... 

European Committee for Standardization, EN 1015-18, Methods of Test for Mortar for Masonry. Determination of Water Absorption Coefficient Due to CapUlary Action of Hardened Mortar, 2002. 

---