Mossbauer spectroscopy
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Mossbauer spectroscopy

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Mossbauer spectroscopy Mossbauer spectroscopy Presentation Transcript

  • Mossbauer spectroscopy And Its Application Presented By: Sakharkar Mohammad Anzar SEM-III MSc-II (2013-2014) Inorganic Chemistry (Paper-II) Ramniranjan Jhunjhunwala College
  • Mossbauer spectroscopy • Mössbauer spectroscopy is a spectroscopic technique based on the Mössbauer effect. This effect, discovered by Rudolf Mössbauer in 1957, consists of the recoil-free, resonant absorption and emission of gamma rays in solids. Fig: Recoil-free emission or absorption of a gamma-ray when the nuclei are in a solid matrix such as a crystal lattice 11 8/14/2013 2Sakharkar Mohammad Anzar
  • Basic principle • Just as a gun recoils when a bullet is fired, conservation of momentum requires a free nucleus to recoil during emission or absorption of a gamma ray. • If a nucleus at rest emits a gamma ray, the energy of the gamma ray is slightly less than the natural energy of the transition, but in order for a nucleus at rest to absorb a gamma ray, the gamma ray's energy must be slightly greater than the natural energy, because in both cases energy is lost to recoil. • This means that nuclear resonance (emission and absorption of the same gamma ray) is unobservable with free nuclei, because the shift in energy is too great and the emission and absorption spectra have no significant overlap. 8/14/2013 3Sakharkar Mohammad Anzar
  • Mössbauer Spectrometer • Source :- Is mountain in solid metal overall weight is increased and doppler bonding and required energy is minimize. – The energy required by sample nuclei for γ- rays absorption will depend on its chemical environment. – The source nuclei should have half life atleast a few weeks. • Collimator :- That filters out non-parallel gamma rays . • Sample:- The solid sample are they contain operated solid metal or crystal form. • Detector :- G.M counter is used as detector; works on principle of ionization of inert gas by high energy of γ-rays. – Hence the current will be directly proportion al to γ-rays coming in. 8/14/2013 4Sakharkar Mohammad Anzar
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  • Mössbauer Spectrum • 3 Types of Nuclear interactions that are observable: • Isomer (chemical, )shifts • Quadrupole splitting • Magnetic (hyperfine) splitting 8/14/2013 6Sakharkar Mohammad Anzar
  • Isomer (Chemical, ) Shifts Isomer shifts – • Results from the electrostatic interaction between the charge distribution of the nucleus and those electrons which have a finite probability of being found around the nucleus(only s electrons have a finite probability of overlapping the nuclear density; can be influenced by p,d electrons by screening the s density from nuclear charge) • Does not lead to splitting of energy levels but results in a slight shift of Mossbauer energy levels in a compound relative to the source 8/14/2013 7Sakharkar Mohammad Anzar
  • Quadrupole Splitting Quadrupole splitting – • The interaction of non-spherical or cubic extranuclear electric fields with the nuclear charge density resulting in splitting of the nuclear energy levels. • For half-integral nuclear spins, the quadrupole interaction results in I + ½ levels for spin I. For integral nuclear spins, the degeneracy of the nuclear levels may be completely removed by quadruple interaction to give 2I + 1 levels. 8/14/2013 8Sakharkar Mohammad Anzar
  • Magnetic (hyperfine) splitting Magnetic splitting – • Is a result of the interaction between the nucleus and any surrounding magnetic field. • The nucleus spin I, splits into 2I+1 sublevels. The selection rules mI= 0, 1 give rise to a symmetric 6-line spectrum. 8/14/2013 9Sakharkar Mohammad Anzar
  • Application • To determine the oxidation state ‘Fe’ in it’s compound:- – Higher the oxidation state mere is the construction of an ion and more is the ‘S’ electron density within the nucleus with lower the nuclear energy level and hence isomer shift is parallel. ION Isomer Shift c/sec Fe2+ 0.10 to +0.18 Fe3+ +0.04 to 0.09 Fe4+ +0.03 Fe6+ -0.06 8/14/2013 10Sakharkar Mohammad Anzar
  • • To study the covalency in the metal-ligand bond in the co-ordination compound:- – If there is significant gap between M & L orbital and ‘L’ electrons one delocalized into metal orbital's then M-L bonds is more covalent. – This results in increasing electron density near the nucleus of metal. – Hence I.S value decreases. Thus covalency of M-L bond can be determine. – If the ligand is donor which is more electronegative then the bond is less covalence & I.S value are high. Compound I.S () FeCl3.6H2O 0.085 FeCl3 0.05 Fe2O3 0.047 K4Fe(CN) 6 0.008 8/14/2013 11Sakharkar Mohammad Anzar
  • • To determine magnetic field in metallic ion. – The metallic ion have cubic geometry hence quadrupole interactions is not expected but still we get 6 lines spectra which can be assign magnetic interactions. – The splitting of lines depend on the internal magnetic field present in given species. – This magnitude can be used to determine internal magnetic field present in the given substance. 8/14/2013 12Sakharkar Mohammad Anzar
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  • Bibliography/Webliography • Gütlich, J.M.; The Principle of the Mössbauer Effect and Basic Concepts of Mössbauer Spectrometry • http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110011995_20110 12265.pdf • http://www.mossbauer.org/currenttopic.html • http://energetika.13s.hu/pub/_atomenergetika_szakirany_/Radioanalitika /2%20ZH_t%E9m%E1i/5_SL-Mossbauer.ppt 8/14/2013 14Sakharkar Mohammad Anzar