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Related Concept Videos

Double Resonance Techniques: Overview01:12

Double Resonance Techniques: Overview

Double resonance techniques in Nuclear Magnetic Resonance (NMR) spectroscopy involve the simultaneous application of two different frequencies or radiofrequency pulses to manipulate and observe two distinct nuclear spins. One important application of double resonance is spin decoupling, which selectively suppresses coupling with one type of nucleus while observing the NMR signal from another nucleus, simplifying the spectrum and enhancing resolution.
Spin decoupling is usually achieved by...
Atomic Nuclei: Nuclear Relaxation Processes01:23

Atomic Nuclei: Nuclear Relaxation Processes

In the absence of an external magnetic field, nuclear spin states are degenerate and randomly oriented. When a magnetic field is applied, the spins begin to precess and orient themselves along (lower energy) or against (higher energy) the direction of the field. At equilibrium, a slight excess population of spins exists in the lower energy state. Because the direction of the magnetic field is fixed as the z-axis,  the precessing magnetic moments are randomly oriented around the z-axis. This...
π Electron Effects on Chemical Shift: Overview01:27

π Electron Effects on Chemical Shift: Overview

An applied magnetic field causes loosely bound π-electrons in organic molecules to circulate, producing a local or induced diamagnetic field over a large spatial volume. As the molecules tumble in solution, the field generated by π-electrons in spherical substituents results in a zero net field. However, the net field generated by π-electrons in non-spherical substituents is not zero. The effect of this induced field depends on the orientation of the molecule with respect to B0, resulting in...
Nuclear Overhauser Enhancement (NOE)01:06

Nuclear Overhauser Enhancement (NOE)

Irradiation of a spin-active nucleus causes an increase or decrease in the signal intensity of neighboring nuclei that are not necessarily chemically bonded or involved in J-coupling. This phenomenon, called the nuclear Overhauser enhancement (NOE), results from through-space interactions between the nuclear spins. The NOE effect decreases with increasing internuclear distance and is generally not observed beyond 4 angstroms. In NOE, dipole-dipole interactions between neighboring spin-active...
NMR Spectrometers: Resolution and Error Correction01:14

NMR Spectrometers: Resolution and Error Correction

When magnetic nuclei in a sample achieve resonance and undergo relaxation, the signal detected in NMR is an approximately exponential free induction decay. Fourier transform of an exponential decay yields a Lorentzian peak in the frequency domain. Lorentzian peaks in an NMR spectrum are defined by their amplitude, full width at half maximum, and position, where the peak width is governed by the spin-spin relaxation time alone. In real experiments, however, the applied magnetic field is rendered...
NMR Spectrometers: Radiofrequency Pulses and Pulse Sequences01:17

NMR Spectrometers: Radiofrequency Pulses and Pulse Sequences

A pulse is a short burst of radio waves distributed over a range of frequencies that simultaneously excites all the nuclei in the sample. Upon passing a radio frequency pulse along the x-axis, the nuclei absorb energy corresponding to their Larmor frequencies and achieve resonance. This shifts the net magnetization vector from the z-axis toward the transverse plane. This angle of rotation of the magnetization vector, or the flip angle, is proportional to the duration and intensity of the pulse.

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Updated: May 18, 2026

In vivo Imaging of Biological Tissues with Combined Two-Photon Fluorescence and Stimulated Raman Scattering Microscopy
09:06

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Published on: December 20, 2021

Relaxation and modulation interference effects in two-pulse electron spin echo envelope modulation (ESEEM).

B Kasumaj1, H Dube, N Zölch

  • 1ETH Zürich, Laboratory of Physical Chemistry, 8093 Zürich, Switzerland.

Journal of Magnetic Resonance (San Diego, Calif. : 1997)
|September 15, 2012
PubMed
Summary
This summary is machine-generated.

Two-pulse electron spin echo envelope modulation (ESEEM) line widths are affected by relaxation. Analyzing unmodulated and modulated ESEEM signal decays reveals insights into spin system relaxation, challenging standard formulas.

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Area of Science:

  • Electron Paramagnetic Resonance (EPR) Spectroscopy
  • Solid-State Chemistry
  • Quantum Mechanics

Background:

  • Two-pulse Electron Spin Echo Envelope Modulation (ESEEM) line widths are influenced by transverse electron spin relaxation.
  • Local field fluctuations induce electron spin relaxation.
  • Standard ESEEM formulas often oversimplify relaxation effects, assuming uniform rates for all transitions.

Purpose of the Study:

  • To investigate the influence of non-uniform relaxation rates on ESEEM signals.
  • To provide a more accurate theoretical framework for analyzing ESEEM data, particularly for spin systems with coupled nuclei.
  • To re-evaluate the interpretation of signal decays in two-pulse ESEEM experiments.

Main Methods:

  • Simultaneous analysis of unmodulated and modulated ESEEM signal decays.
  • Theoretical modeling of spin systems with electron spin 1/2 coupled to N(I) nuclei (spin 1/2).
  • Experimental validation using a single crystal of Cu(II)-doped L-histidine.

Main Results:

  • Experimental data from Cu(II)-doped L-histidine suggest different relaxation rates for allowed and forbidden transitions.
  • Theoretical analysis indicates that product rules for two-pulse ESEEM do not hold when relaxation is considered.
  • Modulation interference significantly impacts the decay of the non-oscillatory part of the two-pulse echo, affecting initial signal features.

Conclusions:

  • Standard ESEEM analysis requires refinement to account for non-uniform relaxation rates.
  • The interpretation of initial signal decay in ESEEM experiments needs to consider modulation interference effects.
  • Accurate analysis of ESEEM signals, especially in complex spin systems, necessitates advanced theoretical treatments beyond simplified models.