In some absorbance spectra in the articles, a region called the Q band can be seen. Where did this name Q come from and what is the physical interpretation of these absorption peaks?
Dear Prof. Ferydon Babaei-Taleshi
In spectroscopy, the term is coined as a Q-branch, altogether with the R-branch and P-branch also called the main transition bands.
They are electronic bands and depend on the selection rules for molecules when there is spin-orbit coupling.
For further information about the physics involved, please look at the monograph:
"Statistical Thermodynamics: An Engineering Approach" by John W. Daily. Cambridge University Press, 2019. Chapter 13 absorption and emission spectroscopy
Best Regards
Careful, do not confuse the Q branch of a vibrational spectrum with the Q band in an UV-Vis spectrum. The Q branch in vibrational spectroscopy is what Pedro L. Contreras E. correctly described.
The Q band is a special absorption constellation with respect to a pi electron system which you can find e.g. in porphyrins which have
- an intense band at low wavelengths called the Soret band, representing the S0->S2 transition
- a series of weak bands at higher wavelengths called the Q band, representing the S0->S1 transition with various vibronic couplings
A full explanation can e.g. be found in
Chapter The Use of Spectrophotometry UV-Vis for the Study of Porphyrins
But I still don't know how it was named and whether it is just a name or it is taken from a personal name or the first letter is a physical quantity. I haven't found anything yet.
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