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Flashcards in EPR Deck (18):

What does EPR stand for

Electron Paramagnetic Resonance


What is EPR used to measure

Species that have an unpaired electron.


What types of atomic species contain unpaired electrons

Free radicals
Transition metals
Defects in materials


What is the difference between dimagnetic and paramagnetic species?

Dimagnetic - all electrons are paired, so no overall spin
Paramagnetic - at least one electron is unpaired, so has overall spin (used in EPR)


How does EPR work

Paramagnetic species placed in a magnetic field. Spin is either parallel to the field (low energy), or antiparallel to the field (high energy).
EPR measures the difference between the electron with high and low energy


What does delta E represent?

The change in energy needed to go from the low energy state to the high energy state


What does delta E equal

= Planck's constant (h)(Js) X frequency (v)(s^-1)
^= hv
= g factor (g)(no unit) X Bohr magneton (muB)(J T^-1) X magnetic field strength (Bo)(T)
^= g[mu]bBo


What is proportional to delta E

Magnetic field strength (Bo)


How is the state of resonance achieved

For an electron to move between energy levels (low/high) it needs to be able to absorb or release (emit) the correct amount of electromagnetic radiation (hv).
When the correct level of radiation is achieved, it is known as resonance energy, and the electron is in a state of resonance


What are the two ways that an electron is brought into a state of resonance

Fixed frequency; varying magnetic field (continuous wave technique)
Fixed magnetic field; varying frequency (time domain/pulsed technique)


What are the key features of the continuous wave technique

When y=0 -> absorbance peak maximum
Maxima and minima are at the midpoint of the absorbance peak
Information recorded as the 1st derivation of the absorption peak graph.


What are the key features of the pulsed technique

Resonance only occurs when correct frequency is obtained. NEEDS FINISHING!


How is EPR different to NMR

Uses higher frequencies (gigahertz, instead of mega)
More sensitive
Weaker magnets needed
Broader lines (graph broader)
Must be carried out at a lower temperature


What are the general components of an EPR instrument

Source (microwave bridge)
Sample (put in EPR tube in magnetic field)
Detector (also in microwave bridge)
Spectrum (output to computer screen)


Name some uses for EPR

Structural biology (nucleic acids, proteins etc)
Find primary sequences, and 3D shape in solution
Helps to work out electron transport processes
May be used in quantum computing


Name some advantages of EPR (vs other methods)

Easier to interpret
Simple systems
Introduction of 'spin labels' - easy to identify


Name some disadvantages of EPR (vs other methods)

Fewer accessible systems (because unpaired electron needs to be introduced


What are the two names for the process of multiple EPR experiments (to measure electron distance)

PELDOR (Pulsed ELectron DOuble Resonance)
DEER (Double Electron Electron Resonance)