Splitting and the spin-orbit interaction (e.g sodium-d lines)

[Erased Citizen]

Hi,
I'm having a little problem understanding why splitting occurs in an atom. For example when you look at the line spectra for Sodium-D, then two lines appear very close together.

I understand that there is a magnetic interaction where the magnetic field has been generated by the orbital motion of the electron within the atom. I think that I read somewhere that the splitting that occurs depends on the quantum number m(l) (the magnetic quantum number). Why then do some atoms emit light with doublet lines, and others do not?

Sorry if this makes absolutely no sense, but I'm trying to get my head around it to understand my Michelson Interferometer experiment where I am measuring the different wavelengths of mercury green/blue/yellow as well as sodium-d lines.

Many thanks for your help

 

[Jhero]

Hello,

Thank you for your question. The splitting of spectral lines in an atom is a phenomenon known as fine structure splitting. This occurs due to the interaction between the electron's spin and its orbital motion within the atom. This interaction is known as spin-orbit coupling.

The magnetic quantum number, m(l), does play a role in determining the magnitude of the fine structure splitting. This is because the value of m(l) determines the strength of the orbital angular momentum, which in turn affects the strength of the spin-orbit coupling.

However, the splitting of spectral lines is not solely dependent on the magnetic quantum number. Other factors, such as the nuclear charge and the electron's energy level, also play a role in determining the splitting of lines.

Some atoms emit light with doublet lines because they have a larger spin-orbit coupling, resulting in a larger fine structure splitting. This is seen in atoms with heavier nuclei, which have a stronger nuclear charge and therefore a stronger spin-orbit coupling.

In contrast, atoms with lighter nuclei may not exhibit doublet lines because their spin-orbit coupling is weaker, resulting in a smaller fine structure splitting. This could explain why you are observing doublet lines in sodium but not in mercury.

I hope this helps clarify the concept of fine structure splitting and its role in the emission of spectral lines. Good luck with your Michelson Interferometer experiment!