Vibrational spectra of hydrogenated and halogenated graphene CX; X = H, F, Cl

Abstract

In this paper, we investigate the Raman and infra-red (IR) spectra of fully hydrogenated and halogenated graphene in a chair, boat and washboard conformations. The IR spectra of chair conformations have two peaks due to Eu and phonons, while their Raman spectra have four peaks due to Eg and phonons. There are low and high frequency in-plane Eg phonons and out-of-plane phonons which give rise to four peaks in the Raman spectra. The optimized structures of the boat and washboard conformations of CH have different point group symmetries. The optical phonons of these conformations of CH are either IR active or Raman active. However, the optimized structures of the boat and washboard conformations of CF and CCl are a bit twisted and have the same (mm2) point group symmetries. In these conformations, there are four Raman active A2 phonons and several other A1, B1 and B2 phonons which are both Raman and IR active.