SE837: Anharmonic infrared spectra of neutral two-, three-, and four-ring PANHs generated via reparameterized semiempirical methods: Benchmarking against experimental spectra and comparison to spectral features in the Orion Bar

A reparameterized PM6 method, recently shown to produce accurate infrared spectra for polycyclic aromatic hydrocarbons (PAHs) containing more than five rings is used here to produce spectra for polycyclic aromatic nitrogen-containing hydrocarbons (PANHs) containing up to four rings. Computed spectra for thirteen molecules, across four classes, are generated, and seven of those are compared to available, experimentally collected spectra. This comparison demonstrates that the reparameterized method efficiently produces accurate spectra for PANHs and allows for the combined spectra of each of these four classes to be compared to spectral features observed in the Orion Bar. The majority of peaks observed in the 5.8-10.6 μm range arise from fundamental, in-plane ring deformations: the presence of a nitrogen atom in one of the rings does not reliably dampen or enhance any of the peaks in a predictable manner. The presence of smaller PANHs in the Orion Bar cannot be conclusively determined, but future work will focus on larger PANHs which are believed to have a higher population than these relatively small examples examined here.