Paschen-Back effect

The Paschen-Back effect refers to the splitting of spectral lines in the presence of a strong magnetic field, which causes the energy levels of atoms or ions to change. This effect is an extension of the Zeeman effect, which describes the splitting of spectral lines due to magnetic fields, but specifically applies to situations where the magnetic field is so strong that it affects the electron orbits around atoms or ions.

Key points about the Paschen-Back effect:

  1. Strong Magnetic Fields: It occurs in the presence of strong magnetic fields, typically much stronger than those where the Zeeman effect is noticeable.

  2. Regime of Application: It is most significant when the product of the magnetic field strength BBB and the wavelength λ\lambdaλ of the emitted light is greater than a certain critical value. This condition ensures that the magnetic field affects the atomic energy levels significantly.

  3. Effect on Spectral Lines: Instead of the usual Zeeman splitting where each spectral line splits into multiple components (often observed in weaker magnetic fields), in the Paschen-Back effect, the lines may split into more complex patterns depending on the specific energy level structure of the atom or ion involved.

  4. Applications: This effect is important in astrophysics and plasma physics, where strong magnetic fields are present (such as in stars or in laboratory plasma experiments), affecting the interpretation of observed spectral lines.

  5. Named after Paschen and Back: The effect is named after Friedrich Paschen and Adolf Back, who studied and provided theoretical explanations for this phenomenon in the early 20th century.

We know that due to spin and orbital motion of electron, electron has certain magnetic field. Zeeman effect is observed if external magnetic field is weak as compared to the internal magnetic field. In this case, precession of l* and s* around J* is much faster than around external magnetic field H. So there are no peturbation between them. If we increase the strength of external magnetic field, then the precession of l* and S* breakdown and precess separately around external field H. This effect is called Paschen - Back effect.

Paschen Back effect of sodium D lines

For the sodium D line i.e 2D5/2 and 2D3/2 the magnetic interaction energy of strong electric field is given by

- ΔT = L (m_l + 2 m_s) + am_lm_s ...1

Equation 1 shows that splitting of sodium D lines occur with respect to the values of (m_l + 2 m_s) and finally with respect to + am_lm_s . Let us tabulate the value of (m_l+ 2m_s) and am_lm_s

The splitting of levels 2D_5/2 and 2D_3/2 in weak and strong field is as shown below.

Understanding the Paschen-Back effect helps in analyzing and interpreting spectral data from various sources, providing insights into the physical conditions and dynamics of environments where strong magnetic fields play a role of electron.

This note is a part of the Physics Repository.