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Related Concept Videos

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...
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NMR Spectroscopy: Spin–Spin Coupling

The spin state of an NMR-active nucleus can have a slight effect on its immediate electronic environment. This effect propagates through the intervening bonds and affects the electronic environments of NMR-active nuclei up to three bonds away; occasionally, even farther. This phenomenon is called spin–spin coupling or J-coupling. Coupling interactions are mutual and result in small changes in the absorption frequencies of both nuclei involved. While nuclei of the same element are involved in...
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: 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.
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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.
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Atomic Nuclei: Nuclear Spin01:08

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All atomic particles possess an intrinsic angular momentum, or 'spin'. Electrons, protons, and neutrons each have a spin value of ½, although protons and neutrons in nuclei may have higher half-integer spins owing to energetic factors.
Atomic nuclei have a net nuclear spin, , which can have an integer or half-integer value. In atomic nuclei, the spins of protons are paired against each other but not with neutrons, and vice versa. Consequently, an even number of protons does not contribute to...

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Measurement of Ultrafast Vibrational Coherences in Polyatomic Radical Cations with Strong-Field Adiabatic Ionization
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Vibronic contributions to hyperfine-mediated spin kinetics.

Anjay Manian1, Holden James Paz1, Haibo Yu1

  • 1School of Science and Molecular Horizons, University of Wollongong, Wollongong, NSW 2522, Australia and ARC Centre of Excellence in Quantum Biotechnology, University of Wollongong, Wollongong, NSW 2522, Australia.

The Journal of Chemical Physics
|May 8, 2026
PubMed
Summary
This summary is machine-generated.

This study introduces a new theoretical framework to model spin evolution in photophysical systems. It reveals that vibronic coupling significantly enhances hyperfine interactions, enabling spin evolution on chemically relevant timescales.

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Area of Science:

  • Chemical Physics
  • Quantum Mechanics
  • Spectroscopy

Background:

  • The Born-Oppenheimer approximation limits kinetic modeling of hyperfine interactions.
  • Spin evolution is crucial in many photophysical systems but often obscured.
  • Accurate modeling of hyperfine interactions is essential for understanding spin-dependent processes.

Purpose of the Study:

  • To develop a unified theoretical framework incorporating vibronic contributions to hyperfine interactions.
  • To investigate the impact of vibronic coupling on spin evolution in radical pairs.
  • To provide a generalized methodology for analyzing hyperfine-driven dynamics.

Main Methods:

  • Developed a theoretical framework using a phase-consistent Herzberg-Teller expansion of the hyperfine Hamiltonian.
  • Incorporated vibronic contributions beyond the Born-Oppenheimer approximation.
  • Applied the framework to the FMNH•-Cys• radical pair system.

Main Results:

  • Second-order vibronic coupling enhances hyperfine-mediated electronic transitions by 10^8-10^9-fold.
  • Observed spin evolution occurs on nanosecond timescales, consistent with experimental observations.
  • Hyperfine interaction rates are significant and comparable to spin-orbit coupling, operating on chemically relevant timescales.

Conclusions:

  • Vibronic descriptions are crucial for accurate modeling of hyperfine-driven dynamics.
  • The developed methodology captures essential non-Condon effects, even at the single-structure level.
  • This work provides a valuable tool for studying systems where full ensemble sampling is impractical.