Absorption, definition

In chemical absorption definite chemical bonds are produced between the atoms and molecules inside the absorbents 1 and the atoms and molecules of the "absorbates"... 

Absorption, definition, 168 Absorption of sound in viscoelastic materials. See Sound absorption in viscoelastic materials Acoustic, definition, 25-26... 

Section BT1.2 provides a brief summary of experimental methods and instmmentation, including definitions of some of the standard measured spectroscopic quantities. Section BT1.3 reviews some of the theory of spectroscopic transitions, especially the relationships between transition moments calculated from wavefiinctions and integrated absorption intensities or radiative rate constants. Because units can be so confusing, numerical factors with their units are included in some of the equations to make them easier to use. Vibrational effects, die Franck-Condon principle and selection mles are also discussed briefly. In the final section, BT1.4. a few applications are mentioned to particular aspects of electronic spectroscopy. 

In spectroscopy it is common for transitions to be observed as absorptive lines because the Boltzmaim distribution, at equilibrium, ensures a higher population of the lower state than the upper state. Examples where emission is observed, which are by definition non-equilibrium situations, are usually cases where excess population is created in the higher level by infiising energy into the system from an external source. 

At first, the dimeric nature of the base isolated from 3-ethyl-2-methyl-4-phenylthiazolium was postulated via a chemical route. Indeed the adduct of ICH, on a similar 2-ethylidene base is a 2-isopropylthiazolium salt in the case of methylene base it is an anilinovinyl compound identified by its absorption spectrum and chemical reactivity (45-47). This dimeric structure of the molecule has been definitively established by its NMR spectrum. It is very similar to the base issued from 2.3-dimethyl-benzo thiazolium (48). It corresponds to 2-(3 -ethyl-4 -phenyl-2 -methylenethiazolinilydene)2-methyl-3-ethyl-4-phenylthiazoline (13). There is only one methyl signal (62 = 2.59), and two series of signals (63= 1.36-3.90, 63= 1.12-3.78) correspond to ethyl groups. Three protons attributed to positions T,5,5 are shifted to a lower field 5.93, 6.58, and 8.36 ppm. The bulk of the ten phenyl protons is at 7.3 ppm (Scheme 22). 

The phenomenological definition for the change in entropy associated with the isothermal, reversible absorption of an element of heat dq is... 

Thickness. The traditional definition of thermal conductivity as an intrinsic property of a material where conduction is the only mode of heat transmission is not appHcable to low density materials. Although radiation between parallel surfaces is independent of distance, the measurement of X where radiation is significant requires the introduction of an additional variable, thickness. The thickness effect is observed in materials of low density at ambient temperatures and in materials of higher density at elevated temperatures. It depends on the radiation permeance of the materials, which in turn is influenced by the absorption coefficient and the density. For a cellular plastic material having a density on the order of 10 kg/m, the difference between a 25 and 100 mm thick specimen ranges from 12—15%. This reduces to less than 4% for a density of 48 kg/m. References 23—27 discuss the issue of thickness in more detail. 

Several additional terms related to the absorption of x-radiation require definition energy of a x-ray photon is properly represented in joules but more conveniently reported in eV fluence is the sum of the energy in a unit area intensity or flux is the fluence per unit time and the exposure is a measure of the number of ions produced in a mass of gas. The unit of exposure in medicine is the Rn ntgen, R, defined as the quantity of radiation required to produce 2.58 x C/kg of air. The absorbed dose for a tissue is a measure of energy dissipated per unit mass. The measure of absorbed dose most... 

Fig. 2. Dual-pressure process using extended absorption for NO abatement. RC = refrigerated cooling see Figure 1 for other definitions.

The absorption band at 300 nm may also be associated with alkah ions, possibly the result of a trapped electron stabili2ed by an alkah ion. The band shifts to longer wavelengths when heavier alkah ions are present, and growth rates for the band show a definite dependence on the type of alkah (205,209). 

The term electrochromism was apparently coined to describe absorption line shifts induced in dyes by strong electric fields (1). This definition of electrocbromism does not, however, fit within the modem sense of the word. Electrochromism is a reversible and visible change in transmittance and/or reflectance that is associated with an electrochemicaHy induced oxidation—reduction reaction. This optical change is effected by a small electric current at low d-c potential. The potential is usually on the order of 1 V, and the electrochromic material sometimes exhibits good open-circuit memory. Unlike the well-known electrolytic coloration in alkaU haUde crystals, the electrochromic optical density change is often appreciable at ordinary temperatures. 

In the dyeing process absorption from the dyebath solution to the fiber eventually stops when an equiHbrium exists between the dye in the fiber phase and the dye in the solution phase. At this point by definition (no movement of dye molecules), therefore... 

It is important to understand that when chemical reactions are involved, this definition of Cl is based ou the driving force defined as the difference between the couceutratiou of un reacted solute gas at the interface and in the bulk of the liquid. A coefficient based ou the total of both uureacted and reached gas could have values. smaller than the physical-absorption mass-transfer coefficient /c . 

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