Radiation, absorbed

Selectivity The selectivity of molecular fluorescence and phosphorescence is superior to that of absorption spectrophotometry for two reasons first, not every compound that absorbs radiation is fluorescent or phosphorescent, and, second, selectivity between an analyte and an interferant is possible if there is a difference in either their excitation or emission spectra. In molecular luminescence the total emission intensity is a linear sum of that from each fluorescent or phosphorescent species. The analysis of a sample containing n components, therefore, can be accomplished by measuring the total emission intensity at n wavelengths. 

The so-called peak power delivered by a pulsed laser is often far greater than that for a continuous one. Whereas many substances absorb radiation in the ultraviolet and infrared regions of the electromagnetic spectrum, relatively few substances are colored. Therefore, a laser that emits only visible light will not be as generally useful as one that emits in the ultraviolet or infrared ends of the spectrum. Further, witli a visible-band laser, colored substances absorb more or less energy depending on the color. Thus two identical polymer samples, one dyed red and one blue, would desorb and ionize with very different efficiencies. 

If energy of the proper frequency is supplied, a transition between these quantum states occurs with the absorption of an amount of energy equal to the separation of the states. The frequency of the absorbed radiation lies in the radio-frequency range and depends on the local magnetic field at the atom in question. 

Molecules such as 3,4 and 5 in Figure 2.6, which have a zero velocity component away from the source, behave uniquely in that they absorb radiation of the same frequency Vj-es whether the radiation is travelling towards or away from R, and this may result in saturation (see Section 2.3.4). If saturation occurs for the set of molecules 3, 4 and 5 while the radiation is travelling towards R, no further absorption takes place as it travels back from R. The result is that a dip in the absorbance curve is observed at Vj-es, as indicated in Figure 2.5. This is known as a Lamb dip, an effect which was predicted by Lamb in 1964. The width of the dip is the natural line width, and observation of the dip results in much greater accuracy of measurement of v es. 

Gas Phase. Gaseous ozone is decomposed to oxygen atoms and molecules by absorbing radiation in the visible and uv spectmm ... 

Depletion of the Ozone Layer. As a constituent of the atmosphere, ozone forms a protective screen by absorbing radiation of wavelengths between 200 and 300 nm, which can damage DNA and be harmful to life. Consequently, a decrease in the stratospheric ozone concentration results in an increase in the uv radiation reaching the earth s surfaces, thus adversely affecting the climate as well as plant and animal life. Pot example, the incidence of skin cancer is related to the amount of exposure to uv radiation. 

Fluorescence and phosphorescence are types of luminescence, ie, emission attributed to selective excitation by previously absorbed radiation, chemical reaction, etc, rather than to the temperature of the emitter. Laser-iaduced and x-ray fluorescence are important analytical techniques (see... 

A new cyanide dye for derivatizing thiols has been reported (65). This thiol label can be used with a visible diode laser and provide a detection limit of 8 X 10 M of the tested thiol. A highly sensitive laser-induced fluorescence detector for analysis of biogenic amines has been developed that employs a He—Cd laser (66). The amines are derivatized by naphthalenedicarboxaldehyde in the presence of cyanide ion to produce a cyanobenz[ isoindole which absorbs radiation at the output of He—Cd laser (441.6 nm). Optimization of the detection system yielded a detection limit of 2 x 10 M. 

Ra.dia.tlon Shielding. Like lead, bismuth absorbs radiation. Therefore, bismuth ahoys are widely used in the medical industry during radiation therapy. The ahoy is molded to the shape of various organs that are to be shielded. Then the molds are placed between the radiation source and the patient to protect the patient s vital organs from radiation exposure. 

The effective absorption of radiation by a gas can be increased by the addition of a sensitizer. For example, when mercuty vapour is added to silane gas, the mercury vapour absorbs radiation to form an excited atom Hg which collides with a silane molecule to lead to partial dissociation... 

For each layer the energy conservation equation is solved. The individual terms are the absorbed radiation in the layer and the radiative and convective heat exchange to the adjacent panes, to the room, or to the exterior. 

Kirchhoff s law The relationship that exists between the absorptivity and emissiv-ity of radiating bodies. It is the capacity of a body to absorb radiation, w hich varies with the wavelength of the incident radiation and the angle of incidence. 

Photophoresis Particle motion that takes place in the direction of radiation, due to the absorbed radiation warming one side of the particle more than the other. 

Molecules that absorb radiation are raised to an excited state. They can return to... 

Since only relatively few substances are capable of emitting fluorescent radiation, they can be particularly selectively detected. This means that the selectivity of the chromatographic separation, which is always aimed at, is meaningfully extended by the selectivity of detection. Accompanying substances that absorb radiation but do not emit light do not interfere when the analysis is made by the selective determination of fluorescence ... 

Spectrometers are designed to measure the absorption of electromagnetic radiation by a sample. Basically, a spectrometer consists of a source of radiation, a compartment containing the sfflnple through which the radiation passes, and a detector. The frequency of radiation is continuously varied, and its intensity at the detector is compar ed with that at the source. When the frequency is reached at which the sample absorbs radiation, the detector senses a decrease in intensity. The relation between frequency and absorption is plotted as a spectrum, which consists of a series of peaks at characteristic frequencies. Its interpretation can furnish structural information. Each type of spectroscopy developed independently of the others, and so the data format is different for each one. An NMR spectrum looks different from an IR spectrum, and both look different from a UV-VIS spectrum. 

A = area of heat transfer, from emitting to or absorbing radiation source, ft. ... 

Microwave ovens emit microwave radiation that is absorbed by water. The absorbed radiation is converted to heat that is transferred to other components of the food. Suppose the microwave radiation has wavelength 12.5 cm. How many photons are required to increase the temperature of 100 mL of water (d = 1 g/mL) from 20°C to 100°C if all the energy of the photons is converted to heat ... 

The radiation sensitivity of polymers and monomers is characterized by a G value the number of radicals formed per 100 e.v. (16 aJ) absorbed. Radiation sensitive groups include -COOH, C-halogen, -S02-, -NH2 and -C=C, Radiation resistant groups are aromatic rings. It appears that the presence of aromatic moieties also offers some degree of radiation protection to the polymer chain as a whole. 

Whereas smokes are often characterized by the mode of their formation, any coned suspension of particles ranging from 0.01 to about 5.0 pm can be considered a smoke. These particles, when suspended in air, reflect, scatter and absorb radiation in a complex manner. A comprehensive model of these interactions in terms of visibility under various conditions was described recently (Ref 62)... 

The absorbed radiation is quickly emitted by the atom, either through stimulated emission or spontaneous emission. Stimulated emission occurs in the... 

The intensity of absorbed radiation. Sunlight or room lights may alter the rate of a reaction. Usually this effect is to be avoided unless the object is to study photochemical effects. The light level in an optical spectrometer that uses monochromatic light is not likely to cause problems, but if white light strikes the sample, as in a diode-array spectrophotometer, this is a possibility. 

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