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Lecture

Spin echoes & coherence transfer

In course

CH-401: Advanced nuclear magnetic resonance

Principles of Magnetic Resonance Imaging (MRI) and applications to medical imaging. Principles of modern multi-dimensional NMR in liquids and solids. Structure determination of proteins & materials. Measurement of molecular dynamics. Principles of Hyperpol ...

Description

This lecture covers the principles of spin echoes and coherence transfer in NMR spectroscopy. It explains the concept of spin precession, the formation of spin echoes, and the refocusing of magnetization. The product operator formalism is used to describe the evolution of coupled spin systems. The lecture also discusses the INEPT experiment, which enhances the sensitivity of low-gamma nuclei by transferring polarization from high-gamma nuclei. Multiple-pulse NMR spectroscopy and the measurement of longitudinal and transverse relaxation rates are explored. The importance of understanding quantum-mechanical vector descriptions in NMR is emphasized.

Instructor

David Lyndon Emsley

Official source

Ontological neighbourhood

Chemistry

Physical chemistry: Spectroscopy

Related concepts (32)

Spin–spin relaxation

In physics, the spin–spin relaxation is the mechanism by which Mxy, the transverse component of the magnetization vector, exponentially decays towards its equilibrium value in nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI). It is characterized by the spin–spin relaxation time, known as T2, a time constant characterizing the signal decay. It is named in contrast to T1, the spin–lattice relaxation time.

Nuclear magnetic resonance spectroscopy

Nuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy or magnetic resonance spectroscopy (MRS), is a spectroscopic technique to observe local magnetic fields around atomic nuclei. This spectroscopy is based on the measurement of absorption of electromagnetic radiations in the radio frequency region from roughly 4 to 900 MHz. Absorption of radio waves in the presence of magnetic field is accompanied by a special type of nuclear transition, and for this reason, such type of spectroscopy is known as Nuclear Magnetic Resonance Spectroscopy.

Nuclear magnetic resonance

Nuclear magnetic resonance (NMR) is a physical phenomenon in which nuclei in a strong constant magnetic field are perturbed by a weak oscillating magnetic field (in the near field) and respond by producing an electromagnetic signal with a frequency characteristic of the magnetic field at the nucleus. This process occurs near resonance, when the oscillation frequency matches the intrinsic frequency of the nuclei, which depends on the strength of the static magnetic field, the chemical environment, and the magnetic properties of the isotope involved; in practical applications with static magnetic fields up to ca.

Two-dimensional nuclear magnetic resonance spectroscopy

Two-dimensional nuclear magnetic resonance spectroscopy (2D NMR) is a set of nuclear magnetic resonance spectroscopy (NMR) methods which give data plotted in a space defined by two frequency axes rather than one. Types of 2D NMR include correlation spectroscopy (COSY), J-spectroscopy, exchange spectroscopy (EXSY), and nuclear Overhauser effect spectroscopy (NOESY). Two-dimensional NMR spectra provide more information about a molecule than one-dimensional NMR spectra and are especially useful in determining the structure of a molecule, particularly for molecules that are too complicated to work with using one-dimensional NMR.

Spin echo

In magnetic resonance, a spin echo or Hahn echo is the refocusing of spin magnetisation by a pulse of resonant electromagnetic radiation. Modern nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) make use of this effect. The NMR signal observed following an initial excitation pulse decays with time due to both spin relaxation and any inhomogeneous effects which cause spins in the sample to precess at different rates. The first of these, relaxation, leads to an irreversible loss of magnetisation.

Related lectures (32)

Spin Coherence: Double Quantum Coherence

Explores spin echo, quadrupolar echoes, and double quantum coherence in spin dynamics.

Spin Relaxation in Magnetic Resonance

Introduces the fundamentals of spin relaxation in magnetic resonance, covering spin-lattice and spin-spin relaxation, and rotational motion in liquids.

NMR Experiments: Basics and Applications

Explores the basic steps in magnetic resonance, including INEPT pulse sequences and two-dimensional NMR experiments like COSY and NOESY.

Introduction to Magnetic Resonance

Covers the fundamental principles of magnetic resonance and its applications in chemistry.

Quantum Description of Pulsed NMR