The D peak in the Raman Spectrum of Graphite is attributed to the breathing mode of $A_{1g)$ symmetry involving phonons near zone boundary. The explanation is the following:

The change of bond polarization with bond length is by far the dominant term in the Raman matrix element for p states. This term is large for the breathing mode of sixfold rings. By symmetry, for a breathing mode of a graphite plane, the contributions from each ring add constructively because of the long-range polarization.

I don't quite understand this explanation: How do I visualize this and why is the change of bond polarization the dominant term. Also why does the Breathing mode have the maximum change? Any clarifications will be appreciated, thanks!


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