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Interactions visible radiation

In absorption spectroscopy a beam of electromagnetic radiation passes through a sample. Much of the radiation is transmitted without a loss in intensity. At selected frequencies, however, the radiation s intensity is attenuated. This process of attenuation is called absorption. Two general requirements must be met if an analyte is to absorb electromagnetic radiation. The first requirement is that there must be a mechanism by which the radiation s electric field or magnetic field interacts with the analyte. For ultraviolet and visible radiation, this interaction involves the electronic energy of valence electrons. A chemical bond s vibrational energy is altered by the absorbance of infrared radiation. A more detailed treatment of this interaction, and its importance in deter-... [Pg.380]

Although this example, at face value, looks to be a case of the use of the absorption of UV/visible radiation to determine the concentration of a single ionic species (the Cu2+ ion) in solution, and, therefore, the province of the previous chapter, it is, in fact, the quantification of a molecular absorption band. In a sulfate solution, the copper ion actually exists, not as a bare ion, but as the pentaquo species, in which the central copper ion is surrounded by five water molecules and a sulfate ion in an octahedral structure (Fig. 4.1). The color of the transition metal ions arises directly from the interaction between the outer d orbital electrons of the transition metal and the electric field created by the presence of these co-ordinating molecules (called ligands). Without the aquation... [Pg.71]

That the hydrated electron is a separate chemical entity has been demonstrated by the technique of pulse radi l sis This consists of subjecting a sample of pure water to a very short pulse of accelerated electrons. The energetic electrons have the same effect upon water as a beam of y-ray photons. Shortly after the pulse of electrons has interacted with the water, a short flash of radiation (ultraviolet and visible radiation from a discharge tube) is passed through the irradiated water sample at an angle of 90° to the direction of the pulse to detect the absorption spectra... [Pg.80]

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. [Pg.18]

Some other materials, such as glass and water, allow visible radiation to penetrate to considerable depths before any significant absorption takes place. Radiation through such scmitranspareiu materials obviously cannot be considered to be a surface phenomenon since the entire volume of the material interacts with radiation. On the other hand, both glass and water ace practically opaque to infrared radiation. Therefore, materials can exhibit different behavior at different wavelengths, and the dependence on wavelength is an important consideration in the study of radiative properties such as emissivity, absorptivity, reflectivity, and transmissivity of materials. [Pg.695]

As shown in Table 25-2, there are two general types of transducers one type responds to photons, the other to heat. All photon detectors are based on the interaction of radiation with a reactive surface either to produce electrons (photoemission) or to promote electrons to energy states in which they can conduct electricity (photoconduction). Only UV, visible, and near-IR radiation possess enough energy to cause photoemission to occur thus, photoemissive detectors are limited to wavelengths shorter than about 2 p.m (2000 nm). Photoconductors can be used in the near-, mid-, and far-IR regions of the spectrum. [Pg.761]

One should remember that the atoms and molecules in liquids are not motionless but in a state of flux determined by the intermolecular interactions and temperature. From the study of microwave spectroscopy discussed in chapter 4, it was found that rotational diffusion processes in liquids are characterized by relaxation times the order of a few picoseconds. When a liquid is irradiated with UV or visible radiation which involves frequencies greater than 10 Hz, the atoms and molecules appear to be motionless because the frequency of the electromagnetic radiation is much greater than that associated with molecular motion (10 Hz and lower). The same is true for infrared spectroscopy except in the... [Pg.205]

This chapter deals with the origin, nature, and measurement of the spectra of molecules arising from the absorption of near-ultraviolet and visible radiation and the dependence of the spectra on molecular structure, reactivity, and interactions with the environment. In addition, the instrumentation employed to obtain the spectra and the techniques used in absorption spectrophotometric analysis are discussed. [Pg.201]

When dealing with low-energy infrared radiation, the interaction with matter is limited to the absorption of light by the outer shell electrons, i.e. those used in forming compounds. Hence, particular bonds will absorb particular wavelengths. This is the principle used for infrared spectroscopy. There are equivalent techniques for ultraviolet radiation and visible radiation, but they are mostly used to provide information about concentration of a given compound, rather than for identification purposes such as XRF or IR techniques. [Pg.16]

Recently, a novel type of integrated optical detectors based on the interaction of radiation with a surface situated in a flowing stream was introduced [848]. Exploiting absorbance, reflectance, and fluorescence of visible and/or UV light as it changes due to chemical reactions taking place at or in close proximity of a surface surrounded by a flowing stream,... [Pg.253]

Ultraviolet and visible radiation have enough energy to cause transitions of the outermost, or bonding, electrons only. X-ray frequencies, on the other hand, are several orders of magnitude more energetic (see Example 6-3) and are capable of interacting with electrons that are closest to the nuclei of atoms. Absorption peaks that correspond to electronic transitions of these innermost electrons are thus observed in the X-ray region. [Pg.153]

The interaction of UV and visible radiation with matter can provide qualitative identification of molecules and polyatomic species, including ions and complexes. Structural information about molecules and polyatomic species, especially organic molecules, can be acquired. This qualitative information is usually obtained by observing the UV /VIS spectrum, the absorption of UV and visible radiation as a function of wavelength by molecules. A typical UV absorption spectrum is shown in Fig. 5.1. The spectrum may be plotted as wavelength vs. absorbance, transmittance, or molar absorptivity, s. The molar absorptivity is defined subsequently. In Fig. 5.1, the absorption spectrum of pyridine dissolved in ethanol is plotted as log s vs. wavelength in angstroms (A). [Pg.318]


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Radiation interactions

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