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Related Concept Videos

Spin–Spin Coupling Constant: Overview01:08

Spin–Spin Coupling Constant: Overview

1.1K
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...
1.1K
Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)01:22

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

1.2K
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...
1.2K
Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)01:20

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

1.2K
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...
1.2K
NMR Spectroscopy: Spin–Spin Coupling01:08

NMR Spectroscopy: Spin–Spin Coupling

1.8K
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...
1.8K
Spin–Spin Coupling: One-Bond Coupling01:17

Spin–Spin Coupling: One-Bond Coupling

1.1K
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,...
1.1K
¹H NMR: Interpreting Distorted and Overlapping Signals01:02

¹H NMR: Interpreting Distorted and Overlapping Signals

1.1K
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...
1.1K

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Direct Imaging of Laser-driven Ultrafast Molecular Rotation
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Extreme events in optically pumped spin-VCSELs.

Yao Zeng, Pei Zhou, Yu Huang

    Optics Letters
    |December 24, 2021
    PubMed
    Summary

    Extreme events (EEs) are predicted in spin-polarized vertical-cavity surface-emitting lasers (spin-VCSELs). This study identifies new EE types and analyzes their statistical distributions and generation factors.

    Area of Science:

    • Nonlinear Optics
    • Laser Physics
    • Quantum Optics

    Background:

    • Spin-polarized vertical-cavity surface-emitting lasers (spin-VCSELs) exhibit complex chaotic dynamics.
    • Extreme events (EEs) are rare, high-amplitude fluctuations observed in various complex systems.
    • Understanding EEs in novel laser systems can reveal fundamental physics and potential applications.

    Purpose of the Study:

    • To predict and characterize extreme events (EEs) in the chaotic dynamics of free-running spin-VCSELs.
    • To identify different types of EEs based on polarization and intensity.
    • To investigate the influence of operational parameters on EE generation and compare with optical feedback systems.

    Main Methods:

    • Numerical prediction of EEs in a spin-VCSEL model.

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  • Classification of EEs into vectorial, scalar, and total intensity types.
  • Statistical analysis of EE distributions and comparison with rogue wave statistics.
  • Analysis of the effects of pump power and pump ellipticity.

    • Main Results:

    • First prediction of EEs in free-running spin-VCSELs.
    • Observation of vectorial EEs (simultaneous dual-polarization pulses), scalar EEs (single-polarization pulses), and a new total intensity EE.
    • EEs follow statistical distributions similar to conventional rogue waves.
    • Pump power and ellipticity significantly affect EE generation.

    Conclusions:

    • Spin-VCSELs provide a novel and simple platform for studying extreme events.
    • The findings offer insights into EE dynamics in complex laser systems.
    • This research opens new avenues for exploring spin-VCSEL physics and applications related to extreme events.