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Related Concept Videos

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.
Atomic Nuclei: Nuclear Spin State Overview01:03

Atomic Nuclei: Nuclear Spin State Overview

NMR-active nuclei have energy levels called 'spin states' that are associated with the orientations of their nuclear magnetic moments. In the absence of a magnetic field, the nuclear magnetic moments are randomly oriented, and the spin states are degenerate. When an external magnetic field is applied, the spin states have only 2 + 1 orientations available to them. A proton with = ½ has two available orientations. Similarly, for a quadrupolar nucleus with a nuclear spin value of one, the...
NMR Spectroscopy: Spin–Spin Coupling01:08

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...
Atomic Nuclei: Nuclear Spin01:08

Atomic Nuclei: Nuclear Spin

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...
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...
Atomic Nuclei: Types of Nuclear Relaxation01:28

Atomic Nuclei: Types of Nuclear Relaxation

Nuclear relaxation restores the equilibrium population imbalance and can occur via spin–lattice or spin–spin mechanisms, which are first-order exponential decay processes.
In spin–lattice or longitudinal relaxation, the excited spins exchange energy with the surrounding lattice as they return to the lower energy level. Among several mechanisms that contribute to spin–lattice relaxation, magnetic dipolar interactions are significant. Here, the excited nucleus transfers energy to a nearby...

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Fast nuclear spin conversion in water clusters and ices: a matrix isolation study.

Russell Sliter1, Melissa Gish, Andrey F Vilesov

  • 1Department of Chemistry, University of Southern California, Los Angeles, California 90089, USA.

The Journal of Physical Chemistry. A
|June 16, 2011
PubMed
Summary

Researchers studied water molecules in solid argon using FTIR spectroscopy. They found that nuclear spin conversion is too fast in water clusters to create pure para-water samples for ice or vapor.

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Area of Science:

  • Physical Chemistry
  • Spectroscopy
  • Quantum Chemistry

Background:

  • Nuclear spin conversion in water molecules is a key phenomenon in understanding water's properties.
  • Previous studies have explored water's behavior in isolation and clusters, but direct observation of spin conversion dynamics in controlled environments is limited.

Purpose of the Study:

  • To investigate the nuclear spin conversion dynamics of water molecules isolated in solid argon.
  • To determine the feasibility of preparing concentrated samples of para-water (para-H2O) for spectroscopic studies.

Main Methods:

  • Isolation of single water molecules in solid argon (Ar) matrices at cryogenic temperatures (4 K).
  • Rovibrational spectroscopy using Fourier Transform Infrared (FTIR) spectroscopy to probe vibrational modes (ν(1), ν(2), ν(3)).
  • Controlled nuclear spin conversion and subsequent annealing to study phase transitions and vapor-phase behavior.

Main Results:

  • Pure para-H2O was prepared via nuclear spin conversion at 4 K.
  • Fast annealing led to the formation of ice particles.
  • FTIR analysis of vapor above condensed water (T ≥ 250 K) revealed rapid reconversion to nuclear spin equilibrium.

Conclusions:

  • Nuclear spin conversion is rapid in water dimers and larger clusters.
  • The fast conversion kinetics preclude the preparation of concentrated para-H2O samples in condensed phases like ice or vapor.
  • This finding has implications for understanding water's behavior in astrophysical environments and condensed matter physics.