Zeeman effect

It discuss the history and mathematical analysis of Zeeman effect.

1. Zeeman Effect L.Bruno Chandrasekar , Assistant Professor, Periyar Maniammai Institute of Science and Technology, Thanjavur

2. The first principal doublet was observed by Zeeman in 1896 when the source of sodium is placed between a powerful electromagnet. The splitting of energy levels in the presence of external magnetic field is said to be Zeeman effect . In the normal Zeeman effect, the number of splitting is three or lesser. Soon after, Lorentz gave the theory for normal Zeeman effect on the basis of classical physics. He theoretically pointed out that these lines should be polarized. Zeeman observed the state of polarization using prisms and he experimentally confirmed the theoretical prediction made by Lorentz. Moreover, he studied the Zeeman pattern in Zn, Cu, Cd and Sn .

3. With the use of the greater dispersion and resolving power instruments, Preston in 1898 observed more than 3 lines in Cr. The Zeeman pattern of the particular series will be the same and it is the characteristics of that series. This is known as Preston’s law . In a weak magnetic field, the number of Zeeman patern is more than three. This is said to be Anomalous Zeeman effect (AZE).

4. In 1902, Paschen and Runge observed the anomalous Zeeman pattern in Na, Cu and Ag. Runge in 1907 gave the theoretical explanation of AZE and he mentioned that all known Zeeman patterns could be expressed as the rational multiples of normal triplet separation. The wavelength separation in the Zeeman pattern is small and hence one can observe with interference spectrometers such as Fabry -Perot interferometer or grating spectrometers with long focal length.

5. The number of lines observed in the Zeeman pattern depends on ( i ) the applied magnetic field and (ii) direction of view with respect to the external field. Zeeman effect is a powerful tool for spectral analysis and used in many physical concepts such as optical pumping. George E. Hale was observed the Zeeman effect in the solar spectra and it was used to conclude that there is strong magnetic field in the sun spot. Later, Houston et. al. observed the Zeeman splitting in Zinc and Cadmium and Harrison observed more than 130 splitting component in Praseodymium .

6. ( i ) Transverse mode: If the view of observation is perpendicular to the external field, then the mode of observed pattern is termed as transverse mode (TM). 3 lines are observed in the Normal Zeeman effect and more than 3 are observed in the AZE. In this mode, the central line is plane polarized with electric field vector parallel to the field while the other lines are plane polarized with the electric vectors perpendicular to the field . (ii) Longitudinal mode: In this mode, the view of observation is parallel to the field. Here the central line is absent whereas the other lines are circularly polarized in the opposite direction to each other.

7. The normal Zeeman effect can be explained by classical and quantum theory whereas the AZE can be explained only by quantum theory which include the spin of electrons. If one considers only the orbital motion of the electron, then the AZE becomes normal Zeeman effect. Normal Zeeman effect is a very good tool to understand correspondence principle.