Radiant spectrum

Current instruments use complex and refined optical systems in order to radiate the cuvette with monochromatic light selected from the radiant spectrum of the light source. A radically different approach may be practical when tunable lasers become available at reasonable prices. 

Collectively, the molecular and atomic emissions displayed in Table 8.1 give a radiant spectrum as shown in Figure 8.7. 

An excess of chlorine, introduced into reaction (8.7) causes a shift to the left and an improvement in the flame saturation of strontium monochloride. Table 8.3 shows the main emission bands/lines for a red star. Figure 8.8 shows the radiant spectrum of a typical red star. 

Table 8.4 lists the main emission bands and lines for the blue star described above while Figure 8.10 shows the associated radiant spectrum where the band spectrum in the 435-526 nm region (due to CuCl) is particularly prominent. 

Figure 8.10 illustrates the radiant spectrum for an improved blue star. 

Figure 8.5 shows the radiant spectrum of a typical red star. 

All of the energy that drives the atmosphere is derived from a minor star in the universe—our sun. The planet that we inhabit, earth, is 150 million km from the sun. The energy received from the sun is radiant energy—electromagnetic radiation. The electromagnetic spectrum is shown in Fig. 17-1. Although this energy is, in part, furnished to the atmosphere, it is primarily received at the earth s surface and redistributed by several... 

The sun radiates approximately as a blackbody, with an effective temperature of about 6000 K. The total solar flux is 3.9 x 10 W. Using Wien s law, it has been found that the frequency of maximum solar radiation intensity is 6.3 x 10 s (X = 0.48 /rm), which is in the visible part of the spectrum 99% of solar radiation occurs between the frequencies of 7.5 X 10 s (X = 4/um) and 2 x 10 s (X = 0.15/um) and about 50% in the visible region between 4.3 x 10 s (X = 0.7 /rm) and 7.5 X 10 s (X = 0.4 /Ltm). The intensity of this energy flux at the distance of the earth is about 1400 W m on an area normal to a beam of solar radiation. This value is called the solar constant. Due to the eccentricity of the earth s orbit as it revolves around the sun once a year, the earth is closer to the sun in January (perihelion) than in July (aphelion). This results in about a 7% difference in radiant flux at the outer limits of the atmosphere between these two times. 

Infrared, ultraviolet, and nuclear magnetic resonance spectroscopies differ from mass spectrometry in that they are nondestructive and involve the interaction of molecules with electromagnetic energy rather than with an ionizing source. Before beginning a study of these techniques, however, let s briefly review the nature of radiant energy and the electromagnetic spectrum. 

The value of the coefficient will depend on the mechanism by which heat is transferred, on the fluid dynamics of both the heated and the cooled fluids, on the properties of the materials through which the heat must pass, and on the geometry of the fluid paths. In solids, heat is normally transferred by conduction some materials such as metals have a high thermal conductivity, whilst others such as ceramics have a low conductivity. Transparent solids like glass also transmit radiant energy particularly in the visible part of the spectrum. 

The absorption spectrum of a pharmaceutical substance depends partially upon the solvent that has been employed to solubilize the substance. A drug may absorb a miximum of radiant energy at a particular wavelength in one solvent but shall absorb practically little at the same wavelength in another solvent. These apparent changes in spectrum are exclusively due to various characteristic features, namely ... 

Transparency Relatively great Absorption of radiant energy is large in infrared and ultraviolet in visible portion of energy spectrum there is relatively little selective absorption, hence is colorless characteristic absorption important in physical and biological phenomena... 

The emitted spectral radiant power (or exitance) or the emitted spectral photon trradiance (or exitance) plotted as a function of the frequency, wavenumber, or wavelength. The corrected emission spectrum has been cor-... 

The photoreductive synthetic process that promotes the assimilation of carbon dioxide into carbohydrates, other reduced metabolites, as well as ATP (synthesis of the latter is termed photophosphorylation). Photosynthesis is the primary mechanism for transducing solar energy into biomass, and green plants utilize chlorophyll a to capture a broad spectrum of solar radiant energy reaching the Earth s surface. Photosynthetic bacteria typically produce NADPH, the reductive energy of which is converted to ATP. 

Quinolizidine alkaloid analysis also utilizes the X-ray method, which is based on the absorption of X-rays, diffraction of X-rays, wavelength, and radiant power measurements of X-rays. When an atom is excited by the removal of an electron from an inner shell, it usually returns to its normal state by transferring an electron from some outer shell to the inner with the consequent emission of energy as an X-ray. The X-ray method is applied to quinolizidine alkaloids which have a crystalline form. In this sense it is the same as the RTG methods, which can be applied only to crystalline materials. X-rays can be absorbed by material and this gives rise to X-ray absorption spectra . The spectrum provides material for the identification of compounds. 

We have shown that the radiant flux spectrum, as recorded by the spectrometer, is given by the convolution of the true radiant flux spectrum (as it would be recorded by a perfect instrument) with the spectrometer response function. In absorption spectroscopy, absorption lines typically appear superimposed upon a spectral background that is determined by the emission spectrum of the source, the spectral response of the detector, and other effects. Because we are interested in the properties of the absorbing molecules, it is necessary to correct for this background, or baseline as it is sometimes called. Furthermore, we shall see that the valuable physical-realizability constraints presented in Chapter 4 are easiest to apply when the data have this form. 

Emission spectrum Radiation from an atom in an excited state, usually displayed as radiant power vs. wavelength. Each atom or molecule has a unique spectrum. The spectra can be observed as narrow line emission (atomic emission spectra) or as quasi-continuous emissions (molecular emission spectra). A mercury plasma emits both line spectra and continuous spectra simultaneously. 

Specular reflection is encountered when the reflecting medium is a smooth polished surface. The angle of reflection is identical to the incident angle of the radiation beam. If the surface is IR absorbent, the relative intensity of reflection is less for wavelengths that are absorbed than for wavelengths that are not. Thus, the plot of reflectance R, defined as the fraction of reflected incident radiant energy versus the wavelength (or wavenumber) appears similar to a transmission spectrum for the sample. 

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