Nuclear resonant excitation spectroscopy

At present, nuclear resonant excitation spectroscopy performed by synchrotron radiation has two major aspects (1) it serves as an extended or alternative method of MOssbauer spectroscopy by providing information on hyperfine interactions, and (2) it is used for element-specific local vibration and diffusion studies. These aspects are introduced in the following O Sects. 26.2 and O 26.3. Other applications in fundamental physics and nuclear physics. 

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. 

The recoilless nuclear resonance absorption of y-radiation (Mossbauer effect) has been verified for more than 40 elements, but only some 15 of them are suitable for practical applications [33, 34]. The limiting factors are the lifetime and the energy of the nuclear excited state involved in the Mossbauer transition. The lifetime determines the spectral line width, which should not exceed the hyperfine interaction energies to be observed. The transition energy of the y-quanta determines the recoil energy and thus the resonance effect [34]. 57Fe is by far the most suited and thus the most widely studied Mossbauer-active nuclide, and 57Fe Mossbauer spectroscopy has become a standard technique for the characterisation of SCO compounds of iron. 

Most of us have encountered nuclear magnetic resonance (NMR) spectroscopy many times in the past, for example when analysing the products of preparative organic chemistry. In NMR spectroscopy, the nucleus of an atom is excited following absorption of a photon (in the radiofrequency region of the electromagnetic spectrum). 

Spectroscopic methods provide rapid, nondestructive ways to determine molecular structures. One of the most powerful of these methods is nuclear magnetic resonance (NMR) spectroscopy, which involves the excitation of nuclei from lower to higher energy spin states while they are placed between the poles of a powerful magnet. In organic chemistry, the most important nuclei measured are 1H and 13C. 

Following the heat-load monochromator, the X-ray bandwidth is narrowed to approximately 1 eV and centered on the nuclear resonance energy (14.4 kev for Fe). The high-resolution monochromator further reduces the X-ray bandwidth to about 1 meV and motorized scanning of this monochromator tunes the energy over a range (typically within 100 meV of the resonance) adequate to explore excitation or annihilation of vibrational quanta. The X-ray flux at the sample is about 10 photons/s ( 10 tW), which is very low compared to typical milliwatt beam powers in laser-based Raman experiments see Vibrational Spectroscopy). Additional X-ray optics may reduce the beam size. The cross section of the beam at the sample point is currently about 0.5 x 0.5 mm at station D of beam line 3ID at APS. 

Nuclear magnetic resonance (NMR) spectroscopy is regarded as one of the most important analytical techniques in chemistry for characterization of molecular structure. In addition to the structural information, NMR spectroscopy also gives quantitative information about the sample constituent. The induced current in the coil can be regarded as linearly dependent on the concentration of the nucleus in the sample. Therefore the resonance integrals in a simple one-dimensional spectrum measured with the excitation-acquisition scheme offer a way to measure absolute amounts of the chemicals present in the sample. Recently, the need for quantitative analysis of highly complex samples has led to a situation where resonance overlap in... 

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