PH3203 - Lecture 7

In this lecture I first describe the effect of spin orbit interaction in the spectra of Alkali atoms. While this is similar to the calculation that we carried out for Hydrogen spectra fine structure in the previous lecture, here I demonstrate the calculation in the l,s,m_l,m_s basis. Note that here we have to diagonalize a non-trivial secular matrix, but the final result leads us back to the l,s,j,m_j basis.

I then go on to describe the Zeeman effect, which is the splitting that happens to the spectral lines in the presence of a magnetic field. We are now investigating a system where there are two different perturbations - the spin-orbit interaction and the Zeeman interaction. Depending on the strength of the magnetic field, one of these terms is applied first, thus partially lifting the degeneracy of the original unperturbed levels. I show how this gives rise to what looks like a "classical" splitting for very large magnetic fields. I then discuss the case of the so-called Anomalous Zeeman Effect - which is the phenomenon that takes place when the magnetic field is weak.