Chemistry

Nuclear Magnetic Resonance Spectroscopy (NMR)

Nuclear Magnetic Resonance Spectroscopy (NMR)



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General information about the relaxation times T1 and T2

The energy absorbed when the resonance frequency is irradiated is given back by relaxation processes; the system returns to its (lower energy) state of equilibrium magnetization.

Energy level display:

Vector illustration:

There are two different relaxation mechanisms:

  1. Longitudinal relaxation or spin-lattice relaxation Relaxation in the direction of the external field, release of energy to the environment
  2. Transverse or spin-spin relaxation Relaxation perpendicular to the direction of the external field, an excited spin state transfers its energy to another spin in the ground state, ratio N1/ N0 stays unchanged

Both processes follow exponentially decaying time laws and are determined by the relaxation times T.1 (Longitudinal relaxation time or spin-lattice relaxation time) or T.2 (Transverse relaxation time or spin-spin relaxation).

These can be in the order of seconds, minutes or even hours.

T2 can be less than or equal to, but never greater than T.1 be.

The relaxation times can be determined experimentally.

They have an influence on the intensity and line shape of the signals.

An example of application outside of the chemistry laboratory is magnetic resonance tomography (MRT), where differences in relaxation times are used for imaging in modern medicine.


Video: Консультация по квантовой механике. Часть 10. Эффект Зеемана. ЭПР и ЯМР (August 2022).