Today I am giving the "cake meeting" talk. I will mostly go through some key ideas about excited states of organic molecules, that I mentioned in the previous post.
The figure below nicely illustrates a few key ideas.
It shows the absorption and emission spectrum of anthracene.
The high energy feature is associated with the lowest "bright" singlet state.
The low energy feature is associated with the lowest triplet state.
Note
- the vibrational satellites (these are mostly aromatic C-C stretches)
- the "mirror-image" symmetry of the absorption and emission spectrum.
- the singlet absorption is 8 orders of magnitude larger than the triplet
- the large singlet-triplet energy gap
I will then flag how the full machinery of quantum many-body theory can attack some (but far from all) of these issues: vibronic structure, mirror-image rule, Huang-Rhys factor, Stokes shifts....
The relevant formalism is contained in a section of Mahan's tome, Many-Particle Physics. It allows one to treat many-modes, temperature dependence, and strong coupling, ...
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