Mossbauer technique

The relevant structural and chemical information on iron-sulfur proteins provided by EPR, ENDOR and Mossbauer techniques serves as an instructive example for the success of combining different types of spectroscopic methods. 

The results are misleading simply because the basic set of functions used is inappropriate. The great value of the Mossbauer technique is that once SR/R is established, one then has a rather severe test to apply to theoretical calculations concerning the structure of compounds. If... 

JJor chemists interested in modem theories of chemical bonding, the most useful data obtainable by the Mossbauer technique are the magnitude and sign of the electric quadrupole field gradient tensor and the magnitude of the shift, 8, (which we prefer to call the chemical isomeric. Cl, shift), of the center of the Mossbauer spectrum relative to some standard absorber. Although a considerable amount of chemical and structural information is potentially available from quadrupole data on iron compounds, relatively little use has been made of such data in the literature, and we will not discuss this parameter here. We will instead restrict ourselves to two main points review of the explanations put forth to explain Cl shift data in iron compounds, and a survey of some of the correlations and generalizations which have been found. 

Rhode, 1971] Rhode, W. (1971). Observations of the vibration of the basilar membrane in squirrel monkeys using the Mossbauer technique. J. Acoust. Soc. Am., 49 1218-1231. 

For comparison with Tables I and II, Table lit gives the range and typical values of the mineral distributions observed in bituminous coals by the CCSEM and Mossbauer techniques, derived from studies of perhaps a hundred different bituminous coal samples in this laboratory. Some obvious differences in mineralogy are apparent. In addition to the difference in calcium dispersion and abundance already noted, it is seen that certain minerals common in bituminous coals, such as Fe-bearing clays (illite and chlorite) and siderite, are virtually absent in the low-rank samples of Tables I and II. Conversely, minerals such as barite (BaSO ), apatite (Ca5(P0 )30H), and other Ca, Sr phosphates are rather uncommon in bituminous coals. 

A number of transition metal nuclei can be studied by Mossbauer techniques (e.g., Fe, Ni, Ru, W, Os, Ir, and Pt). Of these, only Ir, Ru, and Fe have been used to study nitrosyl bonding. The most detailed studies have been on the well-known iron complexes [Fe(CN)5(NO)] - (87. 89) and [Fe(NO)(dtc)z] (88-90) (dtc is N,N-dialkyldithiocarbamato). In the latter, high-spin/low-spin equilibria can be followed by Fe Mossbauer spectroscopy, and the Mossbauer parameters agree well with data from electron spin resonance (ESR) spectroscopy in determining the ground states of these complexes. 

Sellick PM, Patuzzi R, Johnstone BM (1982) Measurement of basilar membrane motion in the guinea pig using the Mossbauer technique. J Acoust Soc Am 72( 1 ) 131-141... 

Since its discovery, Mossbauer spectroscopy has grown into a highly sophisticated technology in which precise measurements (10-8 ev) are made and detailed information about the environment of the Mossbauer nucleus can be found. In the case of 57Fe, the Mossbauer technique has seen its greatest development so that an accurate description of the chemical state of an iron ion can be determined which includes the details of the electronic states and their energies, the symmetries of the crystalline or molecular environment and the covalent sharing of the valence electrons. 

The ESR experiment by Aasa (27) yields two sets of spin Hamiltonian parameters — one for each iron site. A Mossbauer spectrum calculated from each set of Aasa s parameters has been found to be no different from the calculation assuming identical sites. This indicates that the ESR experiment is much more sensitive to small effects than the Mossbauer technique. 

The ordinary (or integral) conversion electron MOssbauer technique thus measures electrons scattered from the surface layer several thousand A deep irrespective of their energies. If we resolve the energy of the scattered electrons by coupling the conversion electron MOssbauer spectrometer with an electron spectrometer, the solid surface can be characterized into a thinner... 

We could thus characterize by the MOssbauer technique the Fe(CO)j (n= 2-4) fragments as the UV-photolysis products of Fe(CO)g in nitrogen matrix. The MHssbauer parameters obtained in an argon matrix were similar to those in the nitrogen matrix. 

MAS-NMR, ESR, UV-vis and Mossbauer techniques appear also to be of great value when applicable and are anyway of great interest. Diffusivity measurements may also give some information if steric hindrance has been created. 

Later studies of the EFG tensor in muscovite by Bonnin and Muller (1981) and Aldridge et al. (1987) quantified the EFG in muscovite, but noted that it is aligned differently in different samples. They attributed these differences to varying Fe and Fe concentrations in edge-sharing M1-M2 and Ml-Ml octahedra. They also made the assumption of equal populations in Ml and M2 sites, which we now know to be unprovable by the Mossbauer technique. 

X 10 for up to 202 mms for Re. They are all very small when compared with the tremendous velocities ( 7 x 10 mm s ) used by Moon in 1950 to detect nuclear resonance fluorescence without recoilless emission, and show dramatically that the Mossbauer technique eUminates both recoil and thermal broadening. The Heisenberg relation means that an excited state with a shorter half-life has a greater uncertainty in the y-transition energy and hence a broader resonance line. 

There are few direct spectroscopic probes for iron for instance, in most complexes charge transfer bands obscure the d-d transitions and magnetic measurements cannot provide information on low-spin iron(II) complexes. Therefore when the Mossbauer technique became generally available in the late 1960s, it was widely used for the study of iron complexes. The effect arises from the resonant absorption of y-rays by the Fe nucleus, which has a natural abundance of 2%. When the y-ray source and sample nuclei are in different environments, the shift in the energy of resonant absorption is expressed as a velocity relative to some arbitrary zero such as stainless steel or Na2[Fe(CN)5N0] 2H20. Whilst the value of the shift is temperature dependent, it is also affected by the electronic environment. 

The above assumption has been confirmed by a recent work on automobile pollution. The iron compoimds emitted into the atmosphere as exhaust were determined with the Mossbauer technique (25). The Mossbauer spectra of the deposit from the car exhaust revealed that the iron compoimds were mainly composed of hematite (a-Fe203) in the form of ultrafine particles 120 A in diameter. In general, we should... 

Corrosion of Metals. Corrosion phenomena of iron, cobalt, tin, and their alloys have been investigated by a variety of Mossbauer techniques by the transmission and scattering methods and by the emission technique in which the specimen under study is doped with a Mossbauer source isotope (e.g., Co) and measured against a single-line resonant... 

Johnstone B.M. and Boyle A.J.F (1967). Basilar membrane vibration examined with the Mossbauer technique. Science 158 390-391. 

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