Resonance, absorption sharp

Like hydride complexes in general, the carbonyl hydrides generally exhibit sharp M—H stretching bands in the infrared and proton nuclear resonance absorptions at very high % values as shown in Table 22-3. 

A correction can also be made with a hydrogen or deuterium continuum source with the monochromator set at the same wavelength as the resonance line. Sharp line-absorption of the continuum source by the test element is negligible compared to the background over the bandwidth of the monochromator, so the absorbance of the continuum source can simply be subtracted from the absorbance of the resonance line. Several commercial instruments have arrangements that allow automatic background corrections with continuum sources. 

Additional confirmation of the statistical model comes from experiments of a quite different nature involving nuclear magnetic resonance. The protons in the water molecule possess a nuclear magnetic moment so that their environment can be investigated by studies of the shape of their resonant absorption line in a steady applied magnetic field. In an isolated water molecule the resonance is very sharp and this is also the case in liquid water for, although... 

Some nuclei, if embedded into a solid matrix, are capable of repulsion-lTee y-ray resonance absorption. Examples of elements are Fe, Ru, and Sn. The extremely sharp resonance line can be used to measure with high resolution the influence of the chemical environment of the nucleus. For details of the experimental equipment the special literature should be consulted, e.g., Scherson. ... 

Unfortunately, the requirements of recoil-free emission and resonant absorption and transmission through the absorber limit the useable energy range of the Mossbauer effect 7-ray to approximately 10-100 keV. Further, in order to obtain rather sharp absorption lines and a reasonable spectral resolution, the mean lifetime of the Mossbauer 7-ray precursor state should be between 1 ns and 100 ns. Further, the Mossbauer nuclide must have a sufficiently high isotopic abundance in the element to yield a usable signal-to-noise ratio over a reasonable acquisition time. Finally, the radioactive source containing the Mossbauer 7-ray precursor state must be easily prepared and have a mean lifetime of several weeks to be practical. These various requirements limit the number of nuclides available for typical Mossbauer spectral studies. 

In Kondo lattices the resonance absorption of the f ions is usually not observable and the systems have to be studied using a further ESR probe, mostly gadolinium. a-Ce is the most prominent mixed-valence system. However, it has been demonstrated that in this compound the 4f electrons do not contribute significantly to the linewidth and to the g-value of the ESR probe (Rettori et al. 1978). Hence, a-cerium was discussed in detail in sect. 4.1. Valence transitions generally evolve slowly as a function of temperature. Besides the well-defined transition in a-cerium another sharp, temperature-induced valence transition has been detected in Ybo.4Ino.6Cu2 (Felner and Nowik 1986). 

The quantity Fj requires some further comment. As we have already noted, Fj can be shown to be equal to the width of the absorption line for the /th transition. However, this statement does not apply to the type of wide line extending over hundreds of wave numbers and more, such as is observed in solutions. These bands are really the result of the superposition of large numbers of sharp transitions each with a Fj of its own. The narrow lines themselves are broadened by collisions and interactions of the molecules with their neighbors. What is observed is merely the resulting envelope. If one wishes to extend the theory of rotatory dispersion into regions of resonance absorption, one must find a method for adding up the contributions of the narrow lines to the optical activity so as to obtain the contribution as evinced by the broad band. And it must be a method that doesn t require specific knowledge of the various Fj. 

The discovery of the resonant absorption of gamma-rays in lr by Rudolf Mossbauer in 1958 was a milestone in nuclear physics because it was formerly assumed that such a phenomenon could never occur due to the large recoil energies involved. The interest for this new finding was nevertheless still limited in the first years, but, a real breakthrough emerged from the fact that many isotopes showed a larger and much more sensitive effect. So, a new technique, called Mossbauer spectroscopy, was bom. The most important feature of this spectroscopic method is the extreme sharpness of the emission line which can easily be... 

In some cases, e.g. in " Np, the resonance lineshape contains in addition tto"the Lorentzian term of eq. (11) a weak dispersion term which has to be taken into account in precise data analysis (Goldwire and Hannon 1977). The situation in " Np is discussed by Asch et al. (1978). Due to the sharpness of F the velocities needed to destroy resonance absorption are quite small, usually in the range of 10 to lOOmm/s. The actual construction of Mossbauer spectrometers will be reviewed briefly in section 3.1. 

The second type is called "resonance" absorption. This is made evident by a sharp rise in absorption at one or more particular energies. 

Electron spin resonance (esr) (6,44) has had more limited use in coal studies. A rough estimate of the free-radical concentration or unsatisfied chemical bonds in the coal stmcture has been obtained as a function of coal rank and heat treatment. For example, the concentration increases from 2 X 10 radicals/g at 80 wt % carbon to a sharp peak of about 50 x 10 radicals/g at 95 wt % carbon content and drops almost to zero at 97 wt % carbon. The concentration of these radicals is less than that of the common functional groups such as hydroxyl. However, radical existence seems to be intrinsic to the coal molecule and may affect the reactivity of the coal as well as its absorption of ultraviolet radiation. Measurements from room... 

The ethanolie filtrate can be concentrated to 10-15 ml. under reduced pressure to obtain 0.3 g. (7%) of crude product, m.p. 187-202°. Unchanged starting material, if present, is concentrated in this second fraction and may be detected by the furan resonance at 8 5.85 in the proton magnetic resonance spectrum or by a sharp infrared absorption... 

Infrared, nuclear magnetic resonance, ultraviolet, optical rotary dispersion and circular dichroism measurements have been used for the spectral analysis of thiiranes. A few steroidal thiiranes have been reported to possess infrared absorption in the range from 580 to 700 cm The intermediate thiocyanate derivatives (RSCN) have a strong sharp peak at 2130-2160 cm the isomeric isothiocyanate (RNCS) shows a much stronger but broad band at 2040-2180 cm. ... 

It would appear that measurement of the integrated absorption coefficient should furnish an ideal method of quantitative analysis. In practice, however, the absolute measurement of the absorption coefficients of atomic spectral lines is extremely difficult. The natural line width of an atomic spectral line is about 10 5 nm, but owing to the influence of Doppler and pressure effects, the line is broadened to about 0.002 nm at flame temperatures of2000-3000 K. To measure the absorption coefficient of a line thus broadened would require a spectrometer with a resolving power of 500000. This difficulty was overcome by Walsh,41 who used a source of sharp emission lines with a much smaller half width than the absorption line, and the radiation frequency of which is centred on the absorption frequency. In this way, the absorption coefficient at the centre of the line, Kmax, may be measured. If the profile of the absorption line is assumed to be due only to Doppler broadening, then there is a relationship between Kmax and N0. Thus the only requirement of the spectrometer is that it shall be capable of isolating the required resonance line from all other lines emitted by the source. 

The IR spectra of the polymer (P) contained two sharp absorptions near 1000 and 1100 cm-- -, indicative of the presence of unsubstituted cyclopentadienyl rings in the products. The 250-MHz - -H-NMR spectrum, shown in Figure 3, contained the expected peaks for the methyl, methylene, and cyclopentadienyl protons, respectively, at 61.52, 1.57 and 4.04 ppm. No olefinic proton resonances were present, and all of the samples of the polymer in Table II exhibited the same - -H-NMR spectrum. 

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