Fermi Interaction of Electrons with Nuclei

[Winga]

Fermi Contact Interaction of Electrons with Nuclei

About this interaction, is it the spins of nuclei which interact with the spins of electrons?

So, if I draw the magnetic field line from the left nucleus via the pair of e- to the right nucleus and there is not anti-parallel field against it, this state will become stable, vice versa?

 

[Winga]

Like this!

 

[Meir Achuz]

I am not sure about your question. Are you referring to the Fermi-Breit contact interaction between the magnetic moments of the nucleus and an electron?
This leads to hyperfine splitting and is not related to stability.
It leads to line splitting with the parallel spin state lying lower.

 

[Winga]

Yes, this is what I want to know.

Actually, I have a problem about the principal of NMR, which is the spin-spin coupling/J-coupling.

I find that some reference books have not told that the spin interaction between two nuclei is via bonding electrons.

From Fermi-contact interaction, the two adjacent nuclei with parallel spin will raise in energy while they are anti-parallel to each other will lower the energy. So, what is this energy belongs to?
The nucleus/nuclei, the system...

 

[Winga]

In this case, there are 3 nuclei and 2 bonds.

I don't understand what is exchange interaction, and what is the orientation of magnetic moment of the middle nucleus should be?

 

[Meir Achuz]

In molecular systems, the F-B contact interaction I described, if between two nucleii, is completely negligible. You must be thinking of a more complicated long range spin interaction mediated, as you say by electrons. This is something else I am not familiar with. Sorry, I can't help you on that.

 

[QMrocks]

i have learned abt hyperfine interactions but not the mediated kind. Can you kindly let us know which book you are using? i would like to find out abt it too.