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Related Concept Videos

¹H NMR: Interpreting Distorted and Overlapping Signals01:02

¹H NMR: Interpreting Distorted and Overlapping Signals

Spin systems where the difference in chemical shifts of the coupled nuclei is greater than ten times J are called first-order spin systems. These nuclei are weakly coupled, and their chemical shifts and coupling constant can generally be estimated from the well-separated signals in the spectrum.
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are slanted or...
Atomic Nuclei: Nuclear Spin State Population Distribution01:14

Atomic Nuclei: Nuclear Spin State Population Distribution

Near absolute zero temperatures, in the presence of a magnetic field, the majority of nuclei prefer the lower energy spin-up state to the higher energy spin-down state. As temperatures increase, the energy from thermal collisions distributes the spins more equally between the two states. The Boltzmann distribution equation gives the ratio of the number of spins predicted in the spin −½ (N−) and spin +½ (N+) states.
Spin–Spin Coupling Constant: Overview01:08

Spin–Spin Coupling Constant: Overview

In bromoethane, the three methyl protons are coupled to the two methylene protons that are three bonds away. In accordance with the n+1 rule, the signal from the methyl protons is split into three peaks with 1:2:1 relative intensities. The methylene protons appear as a quartet, with the relative intensities of 1:3:3:1.
Qualitatively, any spin plus-half nucleus polarizes the spins of its electrons to the minus-half state. Consequently, the paired electron in the hydrogen–carbon bond must have a...
Spin–Spin Coupling: One-Bond Coupling01:17

Spin–Spin Coupling: One-Bond Coupling

Coupling interactions are strongest between NMR-active nuclei bonded to each other, where spin information can be transmitted directly through the pair of bonding electrons. While nuclei polarize their electrons to the opposite spins, the bonding electron pair has opposite spins. Configurations with antiparallel nuclear spins are expected to be lower in energy. When coupling makes antiparallel states more favorable, J is considered to have a positive value. The one-bond coupling constant, 1J,...
Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)01:20

Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)

Two NMR-active nuclei bonded to a central atom can be involved in geminal or two-bond coupling. Geminal coupling is commonly seen between diastereotopic protons in chiral molecules and unsymmetrical alkenes, among others.
The central atom need not be NMR-active because its electrons are affected by the electron polarization of the spin-active atoms. However, spin information is transmitted less effectively than in one-bond coupling, and 2J values are usually weaker than 1J values. The energy of...
Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)01:22

Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)

Vicinal or three-bond coupling is commonly observed between protons attached to adjacent carbons. Here, nuclear spin information is primarily transferred via electron spin interactions between adjacent C‑H bond orbitals. This generally favors the antiparallel arrangement of spins, so 3J values are usually positive.
The extent of coupling depends on the C‑C bond length, the two H‑C‑C angles, any electron-withdrawing substituents, and the dihedral angle between the involved orbitals. The...

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Related Experiment Video

Updated: Jul 28, 2026

Speciation and Bioavailability Measurements of Environmental Plutonium Using Diffusion in Thin Films
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Speciation and Bioavailability Measurements of Environmental Plutonium Using Diffusion in Thin Films

Published on: November 9, 2015

3He spin diffusion measurements in 3He- 4He mixture films

Sheldon1, Hallock

  • 1Laboratory for Low Temperature Physics, Department of Physics, University of Massachusetts at Amherst, Amherst, Massachusetts 01003, USA.

Physical Review Letters
|September 6, 2000
PubMed
Summary

Measurements of helium-3 (3He) spin diffusion in helium-3/helium-4 (3He-4He) films reveal an unexpected peak in diffusion at specific 3He coverages. This finding challenges current predictions for spin dynamics in these quantum fluid mixtures.

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Last Updated: Jul 28, 2026

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Synthesis of Cyclic Polymers and Characterization of Their Diffusive Motion in the Melt State at the Single Molecule Level

Published on: September 26, 2016

Area of Science:

  • Condensed Matter Physics
  • Quantum Fluids
  • Low-Temperature Physics

Background:

  • Studying helium mixtures provides insights into quantum phenomena.
  • Thin films of helium isotopes exhibit unique surface and confinement effects.

Purpose of the Study:

  • Investigate 3He spin diffusion in 3He-4He mixture films.
  • Determine the dependence of spin diffusion on 3He coverage and temperature.
  • Compare spin diffusion with NMR relaxation times (T1, T2) and magnetization.

Main Methods:

  • Utilized Hahn spin echo techniques for spin diffusion measurements.
  • Performed experiments on 3He-4He films adsorbed on Nuclepore substrates.
  • Varied 3He coverage from 0.10 to 0.98 layers at a constant 4He coverage of 5.0 layers.
  • Conducted measurements within a temperature range of 0.030 K to 0.070 K.

Main Results:

  • Observed an unexplained maximum in the 3He spin diffusion coefficient as a function of 3He coverage.
  • Found that the temperature dependence of spin diffusion was weaker than theoretical predictions.
  • Collected comparative data for NMR relaxation times (T1, T2) and magnetization across the studied coverage range.

Conclusions:

  • The observed maximum in 3He spin diffusion suggests complex interactions or phase behavior not fully captured by current models.
  • The deviation in temperature dependence warrants further theoretical investigation into spin dynamics in confined helium mixtures.