In 1896 Zeeman observed that when a light source is placed under the effect of magnetic field it give line spectrum. Thus the spectral line splits into a number of polarized components. The effect of magnetic field on the atomic spectral lines is call as “Zeeman Effect” and the name of the effect is after the name of the scientist.
We know that in an atom, electrons orbit around the nucleus of the atom. Therefore these electrons have a magnetic dipole moment which in turn is associated with its angular momentum. In a magnetic field, it acquires an additional energy and the original energy level is shifted. This energy shift can be negative, positive or zero depending on the angle between the field and magnetic dipole moment.
So Some degenerate energy levels will split into several non-degenerate energy levels with different energies because of the Zeeman effect.
Thus splitting of lines depends upon the strength of the magnetic field and the angular momentum quantum number of atomic level.
Further we can divide Zeeman Effect into two following categories.
- Normal Zeeman Effect
- Anomalous Zeeman Effect
Normal Zeeman Effect
Normal Zeeman effect corresponds to the singlet state i.e. total spin is zero (S=0). So Total Angular momentum is equal to the orbital angular momentum. We can explain this phenomenon classically. The spectral line split into two or three components. Hydrogen and zinc singlet show this effect.
Anomalous Zeeman Effect
Anomalous Zeeman effect corresponds to the multiplet state. Multiplet state means total spin is not equal to zero (S ≠ 0). Thus total Angular momentum is equal to the sum of spin angular momentum and orbital angular momentum. We can explain this phenomenon quantum mechanically. The spectral line split into four or more components.
Basically Zeeman effect gives us the energy shift in atomic levels due to the magnetic field. This shift corresponds to the coupling of electron orbital angular momentum to the external magnetic field.
In conclusion, the normal Zeeman effect occurs when there is no spin magnetic moment. But generally there is not only a magnetic moment of the orbit of an electron state but also a magnetic moment of the electron spin present. This leads to a complex splitting of atomic states in the external magnetic field. This is the case of anomalous Zeeman effect.
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