Quantum mechanical property

Described by quantum number S

Associated with electron spin

Result of electron's intrinsic angular momentum

Zeeman effect

Dependence on magnetic field strength

Absorption of photons

Energy of photons related to magnetic field strength

Provides a stable magnetic field

Supplies the energy for transitions

Enhances microwave field at the sample

Measures the absorption of microwaves

Stable radicals or paramagnetic species

Suitable solvents and matrices

Gaussian or Lorentzian profiles

Width affected by relaxation times and interactions

Measures the ratio of the electron's magnetic moment to its spin angular momentum

Key for identification of paramagnetic species

Due to interaction with nearby nuclei

Provides information on electronnucleus interactions

In chemical reactions and mechanisms

Molecular geometry and electronic structure

Characterization of semiconductors and insulators

Stability and degradation studies

Studies of metal centers in proteins

Measurement of free radicals in biological tissues

Steady microwave and magnetic field

Uses short microwave pulses

Allows for timeresolved studies

Enhances information on complex systems

Examples: ENDOR, ESEEM

Requires special handling and preparation

For detection of weak signals

For analysis of complex spectra