Absorption of radiant energy

Transitions between two quantised energy levels, say from E0 to , correspond to the absorption of radiant energy, and the amount of energy absorbed (AE) is determined by Bohr s equation... 

Among the causes producing irreversibility w7e may instance the forces depending on friction in solids, viscosity of liquids imperfect elasticity of solids inequalities of temperature (leading to heat conduction) set up by stresses in solids and fluids generation of heat by electric currents diffusion chemical and radio-active changes and absorption of radiant energy. 

The chemistry involved in LfV-curable resin systems has been extensively investigated and thoroughly surveyed [88-94]. LfV-radiation polymerization, is in principle, completely analogous to the conventional addition polymerization. A photoinitiator is used in UV polymerization. Its function is the same as the free-radical initiator. A conventional initiator possesses a thermally labile bond which is cleaved to form free-radical species, but the photoinitiator has a bond which breaks upon absorption of radiant energy. Benzoin ethers, benzyldialkyl ketals, benzophenone, and acetophenone derivatives are the important LfV-photoinitiators [95-99]. 

The situation becomes even worse when the Boltzmann formula is used to interpret the absorption of radiant energy by molecules. Electromagnetic radiation considered as a fluctuating electric field interacts with electrons in... 

Walsh, in 1955, described the theoretical principles of atomic absorption spectroscopy10). Briefly, it can be defined as the absorption of radiant energy by ground state atomic vapor. There are several ways of obtaining atomic vapor, but aspiration of a solution into a flame is the most conventient and most widely used method. 

In the unimolecular reactions which are also of the first order, only one molecule takes part in the reaction. The process of activation in unimolecular reactions, if caused by collisions should ordinarily lead to second order reactions. How then the observed rate of reaction could be of first order. If however, the activation is by absorption of the radiant energy, this problem can be avoided. But many unimolecular reactions take place under conditions where there is no absorption of radiant energy. For example... 

Therefore, the view of absorption of radiant energy was found to be unsatisfactory and finally rejected. Lindemann (1922) offered a solution to the problem. 

There are various cardinal factors that govern measurement of absorption of radiant energy, namely ... 

Step-VI The absorption of radiant energy by some atoms into their higher energy levels enable them to radiate energy (atomic absorption) measured by Atomic Absorption Spectroscopy (AAS). 

Transparency Relatively great Absorption of radiant energy is large in infrared and ultraviolet in visible portion of energy spectrum there is relatively little selective absorption, hence is colorless characteristic absorption important in physical and biological phenomena... 

In a purely photochemical reaction the absorption of radiant energy is plainly responsible for the activation. This suggested the possibility that thermal reactions are also due to activation by the thermal radiation which is present at every temperature. The argument was very forcibly presented by Perrin who showed that if the specific rate of a imimolecular gas reaction remains constant, with indefinite diminution in pressure, activation must be by radiation since the number of opportunities for activation by collision also diminishes without limit. In fact, the decomposition of nitrogen pentoxide, the first gas reaction shown to be unquestionably unimolecular, was found to have a specific reaction rate constant over a wide range of pressure, and apparently increasing at very low pressures. ... 

Qualitative Discussion About Product Distribution. Consider the following two ways of treating a beaker containing A First, the contents are uniformly irradiated second, a small stream is continuously withdrawn from the beaker, irradiated, and returned to the beaker the rate of absorption of radiant energy is the same in the two cases. The two schemes are shown in Figs. 8.1 and 8.2. During this process A disappears and products are formed. Is the product distribution of R and S different in the two beakers Let us see whether we can answer this question qualitatively for all values of the rate constants. 

The basis of the photometry method is a comparison of the extent of the absorption of radiant energy at a particular wavelength in a solution of the test material with that in series of standard solutions. Filter photometers are suitable for routine methods that do not involve complex spectra. In practical laboratory work the photometric micromethod was developed for determination of sparteine, lupanine, lupinine, hydroxylupanine and angustifoline. This method, tested on model solutions, is suitable for the determination of alkaloids in vegetal material of very low alkaloid content. 

Fluorescence is caused by the absorption of radiant energy and re-emission of some of this energy in the form of light. The advantages of molecular fluorescence methods over absorption spectrophotometric methods are... 

Excited state. An energy-rich state of an atom or a molecule, produced by the absorption of radiant energy. 

Figure 8.6 Effect of surface roughness on absorption of radiant energy. The rougher the surface, the greater the probability of internal reflection and ultimate absorption.

If these are the energy states of an ensemble of species which are in a thermal equilibrium, then the absorption or emission can be described by Planck s and Kirchhoff s laws. The emitted or absorbed radiant power is released by or incorporated in the thermal reservoir. In this case, the ensemble is known as a thermal radiator or ahsorher and the corresponding process is referred to as thermal emission or absorption of radiant energy. 

The absorption of radiant energy when a beam of light traverses a solution in a cell of length I is given by = sxlc, where c is the molar concentration of the solution and sx is the molar absorption coefficient at a specified wavelength X (Beer s law). This linear relationship between the absorbance (formerly optical density ) and the concentration forms the basis of innumerable methods for determining the... 

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