Astronomical Infrared Bands and Diffuse Interstellar Bands Both Reproduced by Hydrocarbon Pentagon-Hexagon Combined PAH Molecules

Abstract: This study theoretically predicts the specific Polycyclic Aromatic Hydrocarbon (PAH) molecules to reproduce both astronomically observed Infrared Bands (IR) and Diffuse Interstellar Bands (DIB). In our paper, we could reproduce IR by the hydrocarbon pentagon-hexagon combined PAH molecules using Density Functional Theory (DFT). Found molecules were (C53H18), and (C23H12) with two carbon pentagons among hexagon networks. Origin of DIB may come from the molecular orbital excitation. We applied Time-Dependent DFT calculation. In case of (C53H18), by comparing calculation with observed DIB, we found 7 coincide bands among 42 calculated bands within observed band width. For example, neutral (C53H18) shows calculated 577.35nm band coincide well with observed DIB at 577.95nm within 1.55nm observed band width. Mono-cation shows calculated 627.87nm correspond to observed 627.83nm, also for di-cation calculated 635.89nm to observed 635.95nm. For smaller size molecule (C23H12), we found 5 coincide bands, of which mono-cation shows calculated 713.92nm coincide with observed 713.80nm, di-cation shows calculated 653.27nm correlate to observed 653.21nm. By such quantum-chemical survey, we could predict specific PAH molecules floating in interstellar space.