M2L6f_cq.txt

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OK.
So the last thing I want to discuss
is the new feature of two electrons,
is that we have singlet and triplet levels,
so we have a ladder of states which
are singlet states, and then-- and this
is what we just discussed-- let me just make
dash lines-- because of these ferromagnetic spin-spin
interaction, we have triplet states,
which have lower energy, so these
are n equals 2 triplet states, n equals 2 triplet states,
j equals 1, j equals 0, 1, 2.
So, of course, there are transitions
between those levels, and from a P-state,
you can have transitions down to S-state.
The question I have is, what about possible
transitions between triplet and singlet?
So what I want to ask you now with a clicker question
is, what kind-- so those transitions here
are transitions between singlet and triplet,
and the technical term for transitions
between singlet and triplet are intercombination lines.

So the question I have for you is,
what fields or couplings drive singlet-triplet transitions?

I want you to think about the model we have discussed so far.
All we have is Coulomb energy-- Coulomb energy
between the nucleus and the electrons
and between the electrons.
That's it.
We do not put any other terms into the Hamiltonian,
and now we have obtained those wave functions,
we have obtained those energy splittings,
and now we want to ask, are there transitions possible?
So one possibility is that we can drive the transition
with optical fields.
Let's say our dipole operator, which many of you
have encountered in life.
We have already discussed rotating magnetic fields
the first part of the course.
Is it possible to use both magnetic fields
and optical fields?
Or the last answer is none of the above.
It's not possible with any of those fields
to create any kind of transition between singlet and triplet.