Quantum Mechanics: Genesis and Achievements pp 151-164 | Cite as

# Electron Spin and Pauli Equation

## Abstract

The concept of the *electron spin* was developed empirically as a specific component of the angular momentum. It was suggested by many experimental facts and theoretical problems: the anomalous Zeeman splitting of spectra, the Einstein–de Haas and Stern–Gerlach experiments, as well as by some open questions in the Bohr theory of periodic table.

The electron spin was introduced in 1925 by Goudsmit and Uhlenbeck to explain the double splitting of spectral lines in the Stern–Gerlach experiments. This concept appeared to be a realization of the mysterious two-valued degree of freedom introduced by Pauli in 1924 to fix the Bohr theory of the periodic system.

Pauli introduced a new term into the Schrödinger equation, corresponding to the interaction of the spin with magnetic field. This Pauli equation was further completed by the Russell–Saunders spin-orbital coupling. The completed equation implies the Stern–Gerlach double splitting, and the Landé formula for the *gyromagnetic ratio*, as obtained in the ‘old quantum theory’. This Landé formula perfectly explains the Einstein–de Haas experiments and the anomalous Zeeman effect.

In 1927, Sommerfeld applied this spin concept to clarify some open questions in the Drude theory of metals.

## Keywords

Angular Momentum Orbital Angular Momentum Pauli Exclusion Principle Spin Angular Momentum Spin Magnetic Moment## Bibliography

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