Geometries, molecular Rayleigh scattering, Raman and infrared frequencies of polycyclic aromatic hydrocarbons and subunits of graphite studied by DFT methods

Abstract

This study presents a computational investigation of geometric parameters, infrared (IR) and Raman frequencies as well as molecular Rayleigh scattering of polycyclic aromatic hydrocarbons (PAHs), used as models for subunits of larger graphitic materials. DFT functionals B3LYP, ωB97XD and M06-2X with basis sets 6-31+G(d,p), 6-311+G(d,p), aug-cc-pVDZ and aug-cc-pVTZ were utilized in different combinations in the investigation of two molecular systems: 2H-benzo(cd)pyrene and double-layered 2H-benzo(cd)pyrene. Bond lengths and angles of central carbon atoms in the different subunits varied by a maximum of 2% between systems. Calculated Raman spectra compare well with experimental and simulated Raman spectra from the literature of other PAHs, and only to some extent with experimental spectra of graphitic materials. The molecular Rayleigh scattering was found to increase by a factor of 3.5 upon addition of an extra layer to the system.