Overtone and combination features of G and D peaks in resonance Raman spectroscopy of the C78H26 polycyclic aromatic hydrocarbon

We have studied the Raman spectra of C₇₈H₂₆, a polycyclic aromatic hydrocarbon with D_2h symmetry point group resembling a longitudinally confined graphene ribbon (or a graphene island) with armchair edge. The experimental spectra recorded with several excitation laser lines have been compared with the results from a theoretical analysis of the resonant Raman response based on density functional theory calculations. Compared to previous investigation the spectra show better signal‐to‐noise ratio, which allows determining previously unresolved weak spectroscopic features. We have extended our analysis to the overtone and combination region (i.e. above 2000 cm⁻¹) demonstrating the presence of signals attributable to 2G, G + D, 2D, D_j + D_k and G + acoustic‐like modes. Moreover, we have measured the temperature dependence of the G peak position, which turns out to show a similar behavior with respect to that of graphene/graphite. Copyright © 2015 John Wiley & Sons, Ltd.