mossbauer spectroscopy
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Mossbauer SpectroscopyTRANSCRIPT
Mössbauer SpectroscopyFraser Parlane
Rudolf Ludwig Mössbauer, German physicistNobel Prize in Physics, 19611929 - 2011
“Explain it! The most important thing is, that you are able to explain it! You will have exams, there you have to explain it. Eventually, you pass them, you get your diploma and you think, that's it! – No, the whole life is an exam, you'll have to write applications, you'll have to discuss with peers... So learn to explain it! You can train this by explaining to another student, a colleague. If they are not available, explain it to your mother – or to your cat!”
Rudolf Ludwig Mössbauer, 1984
Rudolf Mössbauer
The Mssbauer EffectCommon spectroscopy techniques
Has similarities to NMR spectroscopy
The Mssbauer Effectobserving resonance-fluorescence and the Compton Effect
“The Compton effect can be a nuisance.”
Jeremy Bernstein
Initially
Change in wavelength
Sponge / steel wall analogy
Energies emitted
Graph not to scale
Energies absorbed
The Mssbauer Effectobserving resonance-fluorescence
Two main issues with this technique:
1. The “recoil” of the nucleus as the gamma-ray is emitted or absorbed
2. The splitting caused in the energy levels by the electronic and magnetic environment cause “hyperfine” splitting in the energy levels
The Mssbauer EffectThe Discovery
Mossbauer discovered that when the atoms are within a solid matrix the effective mass of the nuclei is much larger.
• Mass is now effectively the massof the system
• This makes and very small
RESONANCE!
• Resolution is nowvastly increased( in )
Paper / sun comparison
The Mssbauer EffectThe Discovery
High resolution allows for detection of “hyperfine” splitting.
Requirements for high resolution:• Requires low lying excited states (lower)• Lifetime of the excited state (longer)
meets both of these requirementsand is commonly used
Resonnance!
The Mssbauer EffectThe Discovery
Introduction Mssbauer SpectroscopyFundamentals
• Hyperfine interactions (billionth of an electron volt) – this requires very small changes in the energy of the gamma-ray radiation. This is done using the Doppler effect.
Introduction Mssbauer SpectroscopyReading the Spectra
Three properties that can be read from the spectra
1. Isomer shift
2. Quadrupole Splitting
3. Magnetic Splitting
Introduction Mssbauer SpectroscopyIsomer Shift
• Shift cannot be measured directly. It needs to be measured relative to a known absorber. For instance, is often calibrated to alpha iron. Analogous to NMR.
• Measured as “centroid” of the spectrum.
• Used to determine valency states, ligand bonding states, electron shielding and the electronegativity of functional groups (the electric environment).
• Less electron shielding leads to positive isomer shift
Example
More electron shielding positive shiftLess electron shielding negative shift
Introduction Mssbauer SpectroscopyQuadrupole Splitting
• Nuclei with a quantum number have an asymmetrical charge, forming a nuclear quadrupole moment.
The principle component of the EFG
Quadrupole momentA constant
Introduction Mssbauer SpectroscopyMagnetic Splitting
• Zeeman splitting is the result of the nucleus interacting with a magnetic field
From the spin on the electrons polarizing the spin of the nucleus
From the orbital moment of those electronsFrom the dipolar field due to the spin on those
electrons
Splits the field into peaks.
Introduction Mssbauer SpectroscopyMagnetic Splitting
For , this gives six possible transitions for magnetic quantum numbers and transition.
Peak intensities
Introduction Mssbauer SpectroscopyThe Machine
Introduction Mssbauer SpectroscopyApplications
• Sensitive to subtle changes in the environment
• Detection limits in the billionth of an electron volt
• Geology• Moon• Structure and function of enzymes• Analysis of heterobimetallic complexes
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