Radiation Properties of Gases

For nonequilibrium problems involving radiation, assuming local equilibrium for the emission of radiation and inserting Eq. (10.4) into Eq. (103) yields 

The radiation properties of weakly absorbing fluids are usually determined by the experimental setup shown in Fig. 10.3. The fluid fills a container with two windows. One of the windows faces a known radiation source (say a black body) and the other faces a spectroscope which resolves the radiation beam. The container at a uniform pressure and temperature provides a uniform density and absorption coefficient. 

inserting s = L into Eq. (10.7) gives the monochromatic intensity of the radiation at the container exit, 

If the temperature of the container fluid is small compared with the temperature of the black body, 1° 4(0) andEq. (10.8) reduces to its absorption term, 

Defining the monochromatic emissivity as the ratio of the monochromatic intensity of radiation leaving the fluid relative to the monochromatic intensity of the black body at the same temperature, we have from Eq. (10.9) 

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Tien, C.L. Thermal Radiation Properties of Gases in Hartnett, J.P. and Irvine, T.F., eds Advances in Heat Transfer. Volume 5 (Academic Press. New York. 1968)... 

For the radiation properties of gases, and for the effect of radiation on the balance of thermal energy, we need to know the equation governing the balance of radiation energy. The next section is devoted to the development of this equation. 

Of a special astronomical interest is the absorption due to pairs of H2 molecules which is an important opacity source in the atmospheres of various types of cool stars, such as late stars, low-mass stars, brown dwarfs, certain white dwarfs, population III stars, etc., and in the atmospheres of the outer planets. In short absorption of infrared or visible radiation by molecular complexes is important in dense, essentially neutral atmospheres composed of non-polar gases such as hydrogen. For a treatment of such atmospheres, the absorption of pairs like H-He, H2-He, H2-H2, etc., must be known. Furthermore, it has been pointed out that for technical applications, for example in gas-core nuclear rockets, a knowledge of induced spectra is required for estimates of heat transfer [307, 308]. The transport properties of gases at high temperatures depend on collisional induction. Collision-induced absorption may be an important loss mechanism in gas lasers. Non-linear interactions of a supermolecular nature become important at high laser powers, especially at high gas densities. 

Electromagnetic radiation from atmospheric gases is rich with information on species concentrations, temperatures, chemical reaction processes, and other parameters. Measurement of many of the properties of gases using infrared techniques, i.e., by measuring the absorption and emission characteristics of the gases is now common. 

Radiation damage Superconductivity of bombarded metals Variations of thin film properties Simulation of radiation damage e.g. in nuclear power plants Radiation Chemistry Ion sputtering Ion reflection Radiation decomposition of gases... 

The use of the beneficial properties of gases for rapid transportation of the volatile species to a separation equipment and radiation detectors... 

We have studied basic definitions in chemistry, and we have examined the properties of gases, liquids, solids, and solutions. We have discussed chemical bonding and intermolecular forces and seen how chemical kinetics and chemical equilibrium concepts help us understand the nature of chemical reactions. It is appropriate at this stage to apply our knowledge to the study of one extremely important system the atmosphere. Although Earth s atmosphere is fairly simple in composition, its chemistry is very complex and not fully understood. The chemical processes that take place in our atmosphere are induced by solar radiation, but they are intimately connected to natural events and human activities on Earth s surface. 

This definition of electrochemistry disregards systems in which nonequilibrium charged species are produced by external action in insulators for example, by electric discharge in the gas phase (electrochemistry of gases) or upon irradiation of liquid and sohd dielectrics (radiation chemistry). At the same time, electrochemistry deals with certain problems often associated with other fields of science, such as the structure and properties of sohd electrolytes and the kinetics of ioific reactions in solutions. 

Radon constitutes a serious problem because, being a heavy gas, it collects in such places as basements and mine shafts. When inhaled, radon decays in areas where little penetration is require to cause tissue damage. Radiation from a and (3 decay is not of a highly penetrating type, but inside the lungs it does not have to be in order to still cause damage. Table 15.10 shows several properties of the noble gases. 

From the perspective of the atomic spectroscopist, desirable properties of plasmas include high thermal temperature and sufficient energy to excite and ionize atoms which are purposefully introduced for the purposes of analysis. In terms of atomic spectrometry, this means that we would generally wish to measure the absorption or emission of radiation in the near-ultraviolet (180-350 nm) and visible (350-770 nm) parts of the spectrum. In this sense, plasmas have been variously described as electrical flames or partially ionized gases. A working definition for atomic spectrometry could be as follows ... 

In the preceding chapter, we have seen examples of absorption spectra, mostly of non-polar, dense gases. Such absorption arises from dipole moments which atoms or molecules do not possess, unless they are in interaction with other atoms or molecules. For the duration of the interaction, dipoles are induced that absorb and emit radiation. In this Chapter, we will consider the causes and properties of dipole moments induced by intermolecular interactions. 

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