Possible Molecular Origins of the Unidentified Infrared Emission Features in Planetary Nebulae

Researchers are currently unsure which molecules are responsible for spectral features known as the unidentified infrared emission (UIE) bands observed in planetary nebulae. Infrared emission spectroscopy can be used to identify molecules by assigning spectral peaks to specific molecular vibrations. Scientists have speculated that UIE bands come from either polycyclic aromatic hydrocarbons or mixed aromatic/aliphatic organic nanoparticles with heteroatom substitutions. Starting from these proposals, we have systematically calculated the theoretical infrared spectra of various candidate molecules using density functional theory and compared them to the experimental UIE spectra. The calculated infrared spectra of n-butyl linked nitrogen-substituted pyrene and tetracene systems contain most of the UIE features found in planetary nebulae NGC 7027 and IRAS 21282 + 5050. We plan to carry out calculations with larger nitrogen-substituted tetracene and pyrene polymers in an attempt to match the UIE features more closely. These findings are important for understanding the formation and evolution of planetary nebulae. Keywords: UIE features, Infrared, PAH, MAON, Spectroscopy, Astrochemistry, Planetary Nebulae, Computationa