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Chemical isomer shifts

The Eo Coulombic interaction alters the energy separation between the ground state and the excited state of the nucleus, thereby causing a slight shift in the position of the observed resonance line. The shift will be different in various chemical compounds, and for this reason is generally known as the chemical isomer shift. It is also frequently referred to as the isomer shift or chemical shift, but in view of the earlier use of these terms in optical spectroscopy and nuclear magnetic resonance spectroscopy respectively, the longer expression is preferred. A less frequently used synonym is centre shift. [Pg.46]

The electric quadrupole and magnetic dipole interactions both generate multiple-line spectra, and consequently can give a great deal of information. All three interactions can be expressed as the product of a nuclear term which is a constant for a given Mossbauer y-ray transition and an electronic term which can be varied and related to the chemistry of the resonant absorber being studied. [Pg.46]

For many purposes it is adequate to consider the nucleus as a point charge which influences the electrons via the Coulombic potential. However, the [Pg.46]

The mathematical expression of the above concepts is virtually identical to that for the optical isomeric shift in electronic spectra, and as such is well documented [1-5]. One form of the theory is given in the following paragraphs. [Pg.47]

Electrons of charge — e in the field of a point nucleus of charge +Ze experience a normal Coulombic potential and the integrated electrostatic energy will be [Pg.47]


Isomer shifts have been measured in a variety of nickel compounds. In most cases, however, the information concerning chemical bond properties was not very impressive. The reason is that the second-order Doppler (SOD) shift is, in many systems, of comparable magnimde as the real chemical isomer shift, which causes... [Pg.238]

Fig. 1. Mossbauer spectrum showing the chemical isomer shift. Fig. 1. Mossbauer spectrum showing the chemical isomer shift.
Hobson and Campbell reported that the Mossbauer spectrum of a sample of iron oxide on silica gel, which has been calcined at 500°C for 16 hr, showed (65) a small chemical isomer shift of 0.29 mm see -1 and an unusually large quadrupole splitting of 1.87 mm sec-1. This splitting was noted to be larger than 1.60 mm sec-1 calculated by Flinn et al. (17) for a ferric ion in an octahedral environment with 1 oxygen atom missing but less than 2.26 mm sec -1 calculated for the... [Pg.267]

An initial report that the crystal structure of [Co(NH3)e]-[FeCle] is isomorphous with that of ]Co(NH3)6][TlCl6] has been shown to be incorrect. However, the Mossbauer chemical isomer shifts for [Co(en)3][FeCl6] and [Co(NH3)e][FeCl6] of 0.60 + 0.10 and 0.59 0.10 mm./second, respectively, agree with the values found for other hexacoordinate iron(III) compounds and differ considerably from the value of 0.40 mm./... [Pg.50]

Closer inspection of the Sb Mossbauer parameters (79, 19a) showed that the decreasing antimony(V) chemical isomer shifts with decreasing antimony content in materials calcined for long periods or at high temperatures were consistent with increasing electron density at the antimony nuclei. Such data are compatible with the accumulation of electron density over the cationic species as the antimony content approaches 10%. It has... [Pg.107]

Mossbauer studies of americium compounds have shown that changes in the chemical isomer shift, d, with the oxidation state of the americium may be attributed to increases in the electron density at the nucleus resulting from removal of 5/ electrons. ... [Pg.454]

The chemical isomer shift, <5, as measured in a Mbssbauer experiment is a difference in energy between two chemical environments A and B and from... [Pg.48]

Although the nuclear radius effect is the principal factor in producing a shift of the resonance line, there are two other factors, namely temperature and pressure, which are also acting, and it is often forgotten that the term chemical isomer shift is generally applied to the sum effect of all three. The temperature effect can be very important when measuring small differences in 5-electron density at the nucleus and is considered in the next section. [Pg.50]

The existence of a relativistic temperature-dependent contribution to the chemical isomer shift was pointed out independently by Pound and Rebka [6] and by Josephson [7]. The emitting or absorbing atom is vibrating on its lattice site in the crystal. The frequency of oscillation about the mean position is of the order of 10 per second, so that the average displacement during the Mossbauer event is zero. However, there is a term in the Doppler shift which depends on v, so that the mean value is non-zero. [Pg.50]


See other pages where Chemical isomer shifts is mentioned: [Pg.239]    [Pg.155]    [Pg.193]    [Pg.303]    [Pg.11]    [Pg.17]    [Pg.255]    [Pg.256]    [Pg.256]    [Pg.257]    [Pg.257]    [Pg.259]    [Pg.260]    [Pg.267]    [Pg.267]    [Pg.268]    [Pg.271]    [Pg.273]    [Pg.276]    [Pg.277]    [Pg.279]    [Pg.281]    [Pg.117]    [Pg.361]    [Pg.243]    [Pg.801]    [Pg.106]    [Pg.127]    [Pg.502]    [Pg.46]    [Pg.47]    [Pg.47]    [Pg.49]    [Pg.50]    [Pg.50]    [Pg.53]   
See also in sourсe #XX -- [ Pg.11 , Pg.17 ]

See also in sourсe #XX -- [ Pg.521 ]

See also in sourсe #XX -- [ Pg.1397 , Pg.1398 , Pg.1404 , Pg.1405 , Pg.1440 ]




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Chemical Information from Isomer Shifts

Chemical isomer shift absence

Chemical isomer shift elements)

Chemical or Isomer Shift

Effect of pressure on the chemical isomer shift

Iron-57 compounds chemical isomer shift

Isomer shift

Isomers, chemical

Mossbauer chemical isomer shift

Partial chemical isomer shifts

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