Magnetic resonance Flashcards
What are two types of magnetic resonance and how is this possible?
NMR and EPR. Although they are both very different, both of these are possible because there is a magnetic dipole moment associated with the spin (nuclear or electron).
This involves the magnetic dipole moment interacting with the electron component whereas most other spectroscopies we have seen are electric dipole moments interacting with the electron component of the electromagnetic radiation
What are the two types of angular momentum?
Spin angular momentum and orbital angular momentum
What is the Zeeman splitting?
When a magnetic field is applied and so the degeneracy is lifted
What is the selection rule for the Zeeman splitting, deltaMl?
+/- 1
What is spin procession?
When a magnetic field, Bo, is applied to the sample along the z direction, the spin polarisation moves around the field. This is known as spin procession
What is longitudinal relaxation?
When the net magnetisation grows along z axis as spins come into equilibrium with magnetic field.
What is the sensitivity of NMR?
Very small - the population differences are tiny.
Nuclei with tiger gyromagnetic ratios and filed strength have a better sensitivity
What is a rf pulse?
Cannot overcome Bo field along z by applying another field along x so therefore applying a weak radio frequency pulse oscillating at larmor frequency along x can tilt the bulk magnetisation vector away from its equilibrium position
What happens to a signal with relaxation processes?
Weakens it
What are three types of magnet that can be used in NMR? What is the best and why?
Permanent, electromagnet and superconducting.
Superconducting as it has the best strength, homogeneity and stability.
What does an NMR probe do?
Contains the rf coil and houses the sample. Can spin sample and also vary temperature to
What are the two different methods of NMR?
What is more popular and why?
Continuous wave (CW) and FT NMR. FT as it is much faster
Briefly describe continuous wave NMR?
Either keeps magnetic field fixed and varies the frequency of the rf radiation or visa versa
Briefly describe FT NMR?
Intense rf pulses excites lots of different frequencies in the sample in one go
