Reparameterizing PM6 for Polycyclic Aromatic Hydrocarbons

Brent Westbrook

Abstract

Polycyclic aromatic hydrocarbons are the proposed carriers of the unidentified infrared bands found in numerous astronomical environments. Their large size limits the application of quantum chemical methods like coupled cluster theory and even density functional theory, leaving semi-empirical methods as a promising means of computing their vibrational spectra. I will discuss our methods for computing anharmonic vibrational frequencies and rotational constants with MOPAC, as well as using these methods for reparameterizing existing semi-empirical methods, primarily PM6, to reproduce experimental vibrational frequencies using the pbqff program.