Radiation absorbing gases

The most abundant solar radiation absorbent gas of the atmosphere, by far, is O2. Its absorption spectrum was shown in Fig. 5.3, and the most important reaction is photodissociation to create O atoms, reaction (5.18). 

The aluminium absorbs the radiation, heats up and transfers the heat to xenon gas contained in the cell. As the temperature of the gas varies the curvature of a flexible mirror of antimony-coated collodion, forming a part of the cell, changes. Reflection of a light beam from this mirror, which is on the outside of the Golay cell, indicates its curvature and therefore the intensity of radiation absorbed by the cell. 

The interaction between radiation and a mass of gas can be treated as a collision problem. In this case the number of photon-molecule collisions, Nx, in unit length of an absorbing gas is given by... 

The primary reference method used for measuring carbon monoxide in the United States is based on nondispersive infrared (NDIR) photometry (1, 2). The principle involved is the preferential absorption of infrared radiation by carbon monoxide. Figure 14-1 is a schematic representation of an NDIR analyzer. The analyzer has a hot filament source of infrared radiation, a chopper, a sample cell, reference cell, and a detector. The reference cell is filled with a non-infrared-absorbing gas, and the sample cell is continuously flushed with ambient air containing an unknown amount of CO. The detector cell is divided into two compartments by a flexible membrane, with each compartment filled with CO. Movement of the membrane causes a change in electrical capacitance in a control circuit whose signal is processed and fed to a recorder. 

The intensity of infrared radiation at various wavelengths that would be lost from Earth in the absence of greenhouse gases is shown by the smooth line. The jagged line is the intensity of the radiation actually emitted. The maximum wavelength of radiation absorbed by each greenhouse gas is indicated. 

Mossbauer resonance of Zn to study the influence of the gravitational field on electromagnetic radiation. A Ga ZnO source (4.2 K) was used at a distance of 1 m from an enriched ZnO absorber (4.2 K). A red shift of the photons by about 5% of the width of the resonance line was observed. The corresponding shift with Fe as Mossbauer isotope would be only 0.01%. The result is in accordance with Einstein s equivalence principle. Further gravitational red shift experiments using the 93.3 keV Mossbauer resonance of Zn were performed later employing a superconducting quantum interference device-based displacement sensor to detect the tiny Doppler motion of the source [66, 67]. 

Radiation from flames and combustion products involve complex processes, and its determination depends on knowing the temporal and spatial distributions of temperature, soot size distribution and concentration, and emitting and absorbing gas species concentrations. While, in principle, it is possible to compute radiative heat transfer if... 

If the concentration of the absorbing gas is zero in the sample cell, the radiation striking both compartments is the same, and hence the heating is the same and there is no movement of the diaphragm separating... 

We assume that the absorbing gas is of a uniform composition and in thermal equilibrium. The absorption coefficient, which is defined by Lambert s law, Eq. 3.1, is expressed in terms of the probabilities of transitions between the stationary states of the supermolecular system, in response to the incident radiation. Assuming the interaction of radiation and matter may be approximated by electric dipole interaction, i.e., assuming the wavelengths of the radiation are large compared with the dimensions of molecular complexes, the transition probability between the initial and... 

To assess the photochemical potential of a reaction system it is essential to know its absorbance spectrum. The strength of the absorption of UV/VlS radiation as a function of the wavelength X is given by the well known Beer-Lambert law of absorbing molecules in solution (Eq. 3-4) or of absorbing gas phase components (Eq. 3-6). The relationship A = f(X) is called the absorbance spectrum. 

In the gas phase the (napierian) absorbance At is proportional to the partial pressure p of the absorbing species at a specified reference temperature (usually T=298 K) and to the pathlength I of the radiation absorbing column (Eq. 3-6). 

Especially, for AOPs it is essential to note that the absorbance A is an additive property (cf. Braun et al, 1991), with the consequence that the individual compounds of a wastewater or a gas mixture may compete for the absorption of the incident spectral radiant power. Hence, the concentrations C of any radiation absorbing species i present in water or air must be considered as well as their individual molar absorption coefficients Therefore, the Beer-Lambert law changes to Eq. 3-8, which describes the absorbance A of a multi-component mixture at a specified wavelength X. 

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