| Author(s) and Co-Author(s) with Affiliation: MRIDUSMITA BURAGOHAIN(School of Physics, University of Hyderabad, India 500046), AMIT PATHAK(Department of Physics, Institute of Science, BHU, Varanasi-221005) |
| Abstract: The Universe is an inventory of molecules, which are processed in the interstellar medium (ISM) from the beginning of the Universe and play a key role in the evolution of the galaxies. Amongst the remarkable organics in the ISM that generate spectral features in the ISM, polycyclic aromatic hydrocarbons (PAH) or PAH-like molecules are undoubtedly drawing massive attention revealed by their spectral footprints in the form of emission bands, particularly observed in the mid-infrared wavelength range starting from 3 to 20 µm [1,2,3]. These bands are popularly known as “Aromatic Infrared Bands (AIBs)” as suggested by nature of the anticipated carriers. Previous as well as current observations made by ISO, Spitzer, AKARI, SOFIA, SUBARU, JWST etc. have revealed various characteristics of PAH bands including variations among the bands which indicate variants of the suspected carrier. To characterize the variants of PAHs as carriers of various AIBs, calculating theoretical spectra of potentially sustaining PAH molecules in the ISM is inevitable. Earlier studies suggest that nitrogenated PAHs in which a nitrogen heteroatom replaces an inner carbon atom in the PAH structure may account for the short wavelength component of the 6.2 µm emission band [4]. Given the chemical pathways available, the formation of diverse nitrogenated PAH variants is likely unavoidable. Here, we present theoretically obtained synthetic spectra of a few potential variants of nitrogenated PAHs calculated using “Density Functional Theory (DFT)”, which would enable us to classify the observed bands followed by a discussion on the limitation encountered in this approach.
References
[1] Allamandola L. J., Tielens A. G. G. M., Barker J. R., 1989, ApJS, 71, 733
[2] Tielens A. G. G. M., 2008, ARA&A, 46, 289
[3] Li A., 2020, Nature Astronomy, 4, 339
[4] Hudgins, D. M., Bauschlicher, C. W., Jr., & Allamandola, L. J. 2005, ApJ, 632, 316 |
