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Nuclear magnetic resonance (NMR) spectroscopy uses the intrinsic magnetic moment that arises from the spin angular momentum of a spin-active nucleus. [1] If the element of interest has a nuclear spin that is not zero, [1] the nucleus may exist in different spin angular momentum states, where the energy of these states can be affected by an external magnetic field.
The energy diagram for such a system has four energy levels that depend on the spin-states of I and S corresponding to αα, αβ, βα, and ββ, respectively. The W' s are the probabilities per unit time that a transition will occur between the four energy levels, or in other terms the rate at which the corresponding spin flips occur.
A 900 MHz NMR instrument with a 21.1 T magnet at HWB-NMR, Birmingham, UK. Nuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy or magnetic resonance spectroscopy (MRS), is a spectroscopic technique based on re-orientation of atomic nuclei with non-zero nuclear spins in an external magnetic field.
NMR is extensively used in medicine in the form of magnetic resonance imaging. NMR is widely used in organic chemistry and industrially mainly for analysis of chemicals. The technique is also used to measure the ratio between water and fat in foods, monitor the flow of corrosive fluids in pipes, or to study molecular structures such as ...
At room temperature, the number of spins in the lower energy level, N−, slightly outnumbers the number in the upper level, N+. The energy gap between the spin-up and spin-down states in NMR is minute by atomic emission standards at magnetic fields conventionally used in MRI and NMR spectroscopy. Energy emission in NMR must be induced through ...
The Paschen–Back effect is the splitting of atomic energy levels in the presence of a strong magnetic field. This occurs when an external magnetic field is sufficiently strong to disrupt the coupling between orbital and spin angular momenta. This effect is the strong-field limit of the Zeeman effect.
In atomic physics, hyperfine structure is defined by small shifts in otherwise degenerate electronic energy levels and the resulting splittings in those electronic energy levels of atoms, molecules, and ions, due to electromagnetic multipole interaction between the nucleus and electron clouds.
Energy level diagram for the ENDOR method. The right figure illustrates the energy diagram of the simplest spin system where a is the isotropic hyperfine coupling constant in hertz (Hz). This diagram indicates the electron Zeeman, nuclear Zeeman and hyperfine splittings.