Types of energy absorption

Ans. Absorption of energy is expected. The energy may be light energy (of the same energies as are given off in emission), or it may be heat or other types of energy. 

Equation (4.79) shows that Ro, and consequently the transfer rate, is independent of the donor oscillator strength but depends on the acceptor oscillator strength and on the spectral overlap. Therefore, provided that the acceptor transition is allowed (spin conservation) and its absorption spectrum overlaps the donor fluorescence spectrum, the following types of energy transfer are possible ... 

A strong anharmonie interaction between the vibrations approximately described as rXH and vX.ll Y. There is independent evidence for a parametric relationship between the X Y and X—H interim clear distances from diffraction studies. The resulting effect on the vibrational spectrum increases with the anharmonicity and amplitude of both types of vibration, and seems to be most completely described by a type of energy level scheme proposed by Stepanov. A slight extension of this theory proposed here enables it to explain the persistence of broad vX l absorption regions at low temperatures. 

The following trends concerning the energy of this type of corresponding absorption bond are observed for analogous complexes ... 

These few remarks show that the quality of the crystal must be carefully checked before any attribution of structures of the reflectivity spectrum to absorption mechanisms is made at the observed frequencies. Conversely, observation of unexpected strong reflectivity, possibly related to the presence of various thin dips68 in the low-energy wing of the reflectivity, will appear strange if we do not consider the back-face contribution with the dips being signatures of various types of bulk absorption such as impurities. Another, very characteristic dip, with width proportional to kT [hence very sensitive to the temperature see Fig. 2.9 (arrow)], is attributed to phonon-assisted... 

Microspectrometry is an indispensable technique in criminalistic analyses, being a combination of optical microscopy and spectrometry. Microscopy creates, records and interprets magnified images, whereas spectrometry uses emission, absorption and reflection of radiant energy by matter to determine its structure, properties and composition. On the basis of the type of energy applied, microspectrometry can be divided into IR, visual and ultraviolet (UV-vis), and Raman microspectrometry. This group also includes X-ray microspectrometry, in which an electron microscope takes the place of an optical microscope. Infrared and Raman microspectrometry enable determination and comparison of the chemical composition of studied samples UV-vis microspectrometry serves to compare the colour of samples in an objective way that is independent of the observer and X-ray microspectrometry allows determination of the elemental composition. 

A number of investigations have been carried out in order to establish a relation between the character of the spectrum and the mode of the photochemical decomposition, however, none of these attempts were really successful. It seems probable, as was stated by Blacet , that it is not so much the type of the absorption than rather the energy of the absorbed photon that determines the photochemical behaviour. 

Vibrational spectra are of two types [1], infrared and Raman, and arise from two different types of energy exchanges between the molecules under study and electromagnetic radiation. In infrared spectroscopy, a vibrational transition that involves a change in dipole moment results in absorption of an infrared photon. The energy of the absorbed photon is equal to the energy difference between the two vibrational states of the molecule. 

The analysis of the shape of the absorption edge of the high-pressure phase (Fig. 13) shows the existence of two spectral ranges with different types of energy dependence on the absorption coefficient. At high values of absorption it follows the empirical Tauc relation [57] in the case of parabolic band edges (Fig. 13(b)), while at smaller absorption a so-called Urbach or exponential absorption tail [58, 59] is observed (Fig. 13(c)). The existence of this kind of absorption edge is normally related to amorphous semiconductors. The optical absorption gap determined from our experiment is 0.6-0.7 eV and it decreases with pressure (see below). The slope of the Urbach tail, which can be considered as a measure of a random microfield [59] is found to be T=2.6 eV at 160 GPa. This is very close to what one would expect for an amorphous phase with a coordination of 2.5 [59]. 

The relationship between the type of energy and the spectroscopic region where there is absorption is summarized in Table 2.1. 

Note that the only difference between energy and dose buildup factors is the type of gamma absorption coefficient used. For energy deposition, one uses the absorption coefficient for the medium in which energy deposition is calculated for dose calculations, one uses the absorption coefficient in tissue. 

The exposure to radiation is the product of the absorbed dose rate, which is a rate of energy absorption, and the exposure Ume. Most of the injuries listed above are of the threshold type. The dosage received must exceed a minimum before any physiological effect is observed. Above this level, small dose rates for a long period of exposure time are less injurious than an equivalent total dosage comprised of a very-high-level dose rate for a much smaller period of time. From an engineering viewpoint, the dose rate must be expressed in quantitative units as discussed next. 

After absorption of photons a variety of processes can take place. These processes are either isoenergetic (no change in energy) or combined with an energy transfer to other molecules or between different types of energy levels of the molecule itself ... 

To investigate and understand this type of energy transfer processes, one needs to make use of many different spectroscopic techniques, in particular absorption, luminescence, and excitation spectroscopy in the visible and the ultraviolet spectral regions, with which one can obtain information about the electronic excited states. These methods are assumed here to be known to the reader. 

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