Spectrum, dark lines

Absorptionsspektrum absorption spectrum, dark-line spectrum... 

In an actual PES measurement the spectrum in fig. la would be convoluted with a Fermi fimction to yield only the occupied states, as well as broadened by instrument resolution. The dark lined spectrum in fig. lb corresponds to a convolution with a T = 0K Fermi function. In fig. Ic this r = 0K spectrum has been further broadened with a 20meV Gaussian to match the stated resolution of Patthey et al. (1987a) as well as with an 80meV Gaussian to match the best resolution of a measurement at resonance (/ v = 120eV). This then is the expected shape of a typical Ce heavy fermion PES spectrum, while a typical Yb spectrum would mimic the unoccupied states of fig. la broadened by instrument resolution. 

In fig. 32 is shown a simulation of the KR only.) If the temperature is now increased to 300 K, the spectral weight of the Lorentzian representing the KR at 0.04 eV above Ef must be decreased to about half of its intensity (based on fig. 2) and the entire spectrum convoluted with a 300K Fermi fimction in order to simulate the 300 K spectrum. The result is shown as the dark line spectrum superimposed on the 300 K data. Immediately we see that far too much temperature dependence is predicted, and it would take a severe renormalization of the theory to bring the temperature dependence in line. More importantly, however, the centroid of the simulated peak shows a positive energy shift while experimentally the peak actually shifts away from the Fermi energy with increasing temperature. 

It would be decades before the connection between Fraunhofer s hnes and the absorption lines of metal atoms in the dark line spectrum would be made. It would be decades more before the dark hne spectrum would be utihzed fuUy, by way of Australia, in the analytical technique known today as atomic absorption spectroscopy [26]. 

In 1817, Josef Fraunhofer (1787-1826) studied the spectrum of solar radiation, observing a continuous spectrum with numerous dark lines. Fraunhofer labeled the most prominent of the dark lines with letters. In 1859, Gustav Kirchhoff (1824-1887) showed that the D line in the solar spectrum was due to the absorption of solar radiation by sodium atoms. The wavelength of the sodium D line is 589 nm. What are the frequency and the wavenumber for this line ... 

If we pass white light through a vapor composed of the atoms of an element, we see its absorption spectrum, a series of dark lines on an otherwise continuous spectrum (Fig 1.11). The absorption lines have the same frequencies as the lines in the emission spectrum and suggest that an atom can absorb radiation only of those same frequencies. Absorption spectra are used by astronomers to identify elements in the outer layers of stars. 

The science of spectroscopy is rooted in the work of Joseph von Fraunhofer, a German physicist. He separated sunlight into its component colors using high quality diffraction gratings and prisms. In 1814, he discovered hundreds of dark lines in the sun s spectrum, now called Fraunhofer lines. He could not, however, explain their source. Scientists know now that the lines are caused by elements near the sun s surface absorbing radiation produced in the sun s interior. 

Figure 1-3. Comparison between experimental and theoretically derived spectra for prephenate anion in solution. The vertical lines correspond to the theoretical spectrum for 12 conformers (3 lines for each) with intensities computed as described in the main text. The experimental spectrum is presented as a dark line (with the highest energy intensity also normalized to 1). The inset shows the near-UV absorption in greater detail. Adapted from Ref. [18]...

Although it proved possible to conclude from the results of further experiments with the perester that succinimidyl radicals from this source could abstract benzylic hydrogen from toluene, the reaction system presented further difficulties which are still unresolved. For example, when solutions of NBS and MBN are mixed in the dark, a high concentration of [32] is immediately produced. Whilst this helped to establish the origin of the 27-line spectrum, it constitutes a fresh mechanistic puzzle. 

Fig. 4.3. Photograph of the oscillographic output of the electron ionization TOF spectrum of xenon on a Bendix TOF-MS. The dark lines are a grid on the oscillographic screen. (For the isotopic pattern of Xe cf. Fig. 3.1.) Adapted from Ref. [20] with permission. Pergamon Press, 1959.

Fraunhofer linee spect The dark lines constituting the Fraunhofer spectrum. fraun, hof-or, lTnz ... 

In 1814 Joseph Fraunhofer, a young German physicist who had had thorough training in the art of glassmaking, made an unusually fine prism, saw for the first time the dark lines in the sun s spectrum, and... 

Fox Talbot (24), an English scientist, found in 1834 that, with the aid of a prism, he could distinguish lithium from strontium, even though the salts of both give red flames (4, 26, 32). He stated that the dark lines previously observed by Sir David Brewster (33) in the spectrum of light which had passed through vapors of nitrous acid were caused by absorption of light (5,25). 

Spectroscopy is generally considered to have started in 1666, with Newton s discovery of the solar spectrum. Wollaston repeated Newton s experiment and in 1802 reported that the sun s spectrum was intersected by a number of dark lines. Fraunhofer investigated these lines—Fraunhofer lines—further and, in 1823, was able to determine their wavelengths. 

A very familiar example is the spectrum of sunlight, which is crossed by innumerable dark lines, the Fraunhofer lines, much has been learned about the constitution of llie sun, stars, and oilier astronomical objects from the Fraunhofer lines. 

Sodium salts, when heated in a flame, give that flame a bright yellow color, and this color matches the two brightest lines in the emission spectrum of sodium. Sodium is found widely in nature, and lots of substances produce these lines. Fraunhofer had found that the spectrum of a candle flame contained two bright lines precisely corresponding to two dark lines, known as the D lines, in the emission spectrum of the sun. 

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