Raman Spectra and Structure of sp2 Carbon-Based Materials: Electron–Phonon Coupling, Vibrational Dynamics and Raman Activity

We will focus in this paper on several common features which dominate the Raman spectra of carbon materials, whenever delocalised pi electrons are present. A molecular approach, based on high level quantum chemical calculations and experiments on molecular models, allows to predict the evolution of these features with the relevant structural parameters, namely the size and topology of the conjugated domains. These results allow to obtain insight on the effect of the confinement (both in one and in two dimensions) of conjugated electrons in terms of electronic structure as well as of nuclear geometries. On the other hand, the relevant physical mechanisms which rule the spectroscopic response of theses systems can be successfully predicted in a very simple and general way in the frame of the Hueckel theory. The generalisation of this theory to the determination of a vibrational potential for a two dimensional crystals (graphene) and for carbon nanotubes of any diameter and chirality is presented and discussed in this work.