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Electron Spin Resonance

Electron Spin Resonance. Sara Lim & Elizabeth Ann Pollock University of Rochester PHY 243: Advanced Lab Professor Regina Demina. External Magnetic Field. Apply an external magnetic field  . Zeeman Effect Energy Splitting:. Landé Factor: .

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Electron Spin Resonance

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  1. Electron Spin Resonance Sara Lim & Elizabeth Ann Pollock University of Rochester PHY 243: Advanced Lab Professor Regina Demina

  2. External Magnetic Field Apply an external magnetic field  Zeeman Effect Energy Splitting: Landé Factor: For a Spin ½ system with a free electron (and zero angular momentum), g= 2

  3. Spin in an External Magnetic Field • In an external magnetic field, the spin is either parallel or anti-parallel to applied magnetic field • m = +1/2,-1/2 • the energy levels: or

  4. Resonance When the levels have spacing ΔE||H the oscillatory magnetic field exerts a torque on the dipoles  some of them reverse orientation, ie, they change energy levels: RESONANCE An electromagnetic field can induce magnetic dipole moment transitions if its frequency is near the energy difference: Precessing

  5. Set-up

  6. Set-up

  7. Samples

  8. Differences in samples Valance electron acts analogously to H atom which has a free electron, so applying a magnetic field and sweeping allows observance of resonance It is harder to observe resonance by sweeping magnetic field because ‘subshell’ of molecule is filled, so only a few electrons are free in copper sulfate complex. They are held closer to the complex, so they alternate spin up/down given the relaxation time. The inverse of the relaxation time- the time to reach equilibrium in spin states- is the width of the absorption peak.

  9. DPPH Calculations (in cgs units) Values obtained in lab (via gaussmeter and wavemeter)

  10. Errors/Uncertainty Error in B-field - study with function generator - Imperfect B-field

  11. Problems • Oscilloscope dials • Do not apply more than 20 amps when sweeping the applied B field because the fuse will blow!

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