Resonance, absorption broad

It is a matter of historical interest that Mossbauer spectroscopy has its deepest root in the 129.4 keV transition line of lr, for which R.L. Mossbauer established recoilless nuclear resonance absorption for the first time while he was working on his thesis under Prof. Maier-Leibnitz at Heidelberg [267]. But this nuclear transition is, by far, not the easiest one among the four iridium Mossbauer transitions to use for solid-state applications the 129 keV excited state is rather short-lived (fi/2 = 90 ps) and consequently the line width is very broad. The 73 keV transition line of lr with the lowest transition energy and the narrowest natural line width (0.60 mm s ) fulfills best the practical requirements and therefore is, of all four iridium transitions, most often (in about 90% of all reports published on Ir Mossbauer spectroscopy) used in studying electronic stractures, bond properties, and magnetism. 

This chapter deals mainly with (multi)hyphenated techniques comprising wet sample preparation steps (e.g. SFE, SPE) and/or separation techniques (GC, SFC, HPLC, SEC, TLC, CE). Other hyphenated techniques involve thermal-spectroscopic and gas or heat extraction methods (TG, TD, HS, Py, LD, etc.). Also, spectroscopic couplings (e.g. LIBS-LIF) are of interest. Hyphenation of UV spectroscopy and mass spectrometry forms the family of laser mass-spectrometric (LAMS) methods, such as REMPI-ToFMS and MALDI-ToFMS. In REMPI-ToFMS the connecting element between UV spectroscopy and mass spectrometry is laser-induced REMPI ionisation. An intermediate state of the molecule of interest is selectively excited by absorption of a laser photon (the wavelength of a tuneable laser is set in resonance with the transition). The excited molecules are subsequently ionised by absorption of an additional laser photon. Therefore the ionisation selectivity is introduced by the resonance absorption of the first photon, i.e. by UV spectroscopy. However, conventional UV spectra of polyatomic molecules exhibit relatively broad and continuous spectral features, allowing only a medium selectivity. Supersonic jet cooling of the sample molecules (to 5-50 K) reduces the line width of their... 

There are, however, certain misleading aspects to which attention should be drawn. One is that absence of a detectable resonance absorption does not mean that damage is negligible since, on the one hand, the major breakdown products may be diamagnetic whilst, on the other, absorption may simply be undetectable because the lines are too broad for one reason or another. 

The re-establishment of the thermal population of energy levels after excitation with the pulse of RF energy is brought about by a number of mechanisms. The principal processes are spin-lattice and spin-spin relaxation, designated Tlt and T2, respectively. Tt and T2 tend to be short for nuclei with I> %, with rapid relaxation which often leads to wide resonance absorptions, sometimes so broad that no resonance can be detected. The effect of quadrupole moment on... 

The width AH0 of the resonance absorption curve measured at half peak power - the 3 dB resonance line width - should in general be as small as possible since this implies a narrow range of frequencies over which strong interaction with the ferrite can occur however, there are certain broad-band applications where this would not be the requirement. There are two main contributions to the linewidth ... 

Although a number of possible applications of the Mossbauer effect have been suggested in the previous chapters, it is worthwhile to consider its use in general terms before developing the theme of more specific chemical application. Generally speaking, three broad areas can be defined in addition to that of the basic phenomenon of resonant absorption itself namely relativity and general physics, nuclear physics, and solid-state physics and chemistry. 

A number of workers (2) have noted a broad electron-spin resonance with a g value of about 2 in coals and in charcoals formed below 600°. We wish to report results obtained in the spin-resonance absorption of various preparations of charcoal and the effect of the adsorption of oxygen and nitric oxide on it. 

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. 

Figure 5.9 Mossbauer absorption spectrum of metmyoglobin at T = 295 Thick line fit of the Brownian oscillator model to the data. Dashed line elastic nuclear resonance absorption. Thin lines broad lines due to overdamped harmonic oscillations. Characteristic times given by the width of these broad Lorentzians are 0.87, 0.44, 0.29 and 0.22 ns. 2005 Elsevier Ltd.

Figure 2. Qualitative illustration of the origin of the broad lines in the NMR spectra of abundant spins in solids. (a) A nuclear magnetic moment, sees a net local field arising from all the other spins, typified by iy (b) The resonance absorption is spread out over a range of frequency due to the spread of local field values, largely determined by the statistics of spin-up and spin-down states.

The Goeppert-Mayer two- (or multi-) photon absorption, mechanism (ii), may look similar, but it involves intennediate levels far from resonance with one-photon absorption. A third, quasi-resonant stepwise mechanism (iii), proceeds via smgle- photon excitation steps involvmg near-resonant intennediate levels. Finally, in mechanism (iv), there is the stepwise multiphoton absorption of incoherent radiation from themial light sources or broad-band statistical multimode lasers. In principle, all of these processes and their combinations play a role in the multiphoton excitation of atoms and molecules, but one can broadly... 

The proton magnetic resonance spectrum (carbon tetrachloride) consists of a broad methine signal centered at S 2.55 and a methyl singlet at 8 1.53 superimposed upon a methylene absorption at 8 1.25-1.85. Vapor phase chromatographic analysis denoted a purity of >98%. 

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. ... 

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