Raman Spectra and Structure of sp ² Carbon-Based Materials: Electron–Phonon Coupling, Vibrational Dynamics and Raman Activity

Abstract

We focus on several common features that dominate the Raman spectra of carbon materials whenever delocalised π electrons are present. A molecular approach, based on high–level quantum chemical calculations and experiments on molecular models, allows us to predict the evolution of these features with the relevant structural parameters, namely the size and topology of the conjugated domains. These results allow us to obtain insight on the effect of the confinement (in both 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 that govern the spectroscopic response of theses systems can be successfully predicted in a very simple and general way in the frame of the Hückel theory. The generalisation of this theory to the determination of a vibrational potential for a two–dimensional (2D) crystal (graphene) and for carbon nanotubes of any diameter and chirality is presented and discussed in this work.