Astronomical Diffuse Interstellar Bands Analyzed by Hydrocarbon Pentagon-Hexagon Combined PAH Molecules

This study theoretically predicted the specific Polycyclic Aromatic Hydrocarbon (PAH) molecules to satisfy both astronomically observed Diffuse Interstellar Bands (DIB) and Infrared Bands (IR). Under astronomical top-down material creation scheme, we have previously found the hydrocarbon pentagon-hexagon combined PAH molecules by comparing observed IR with Density Functional Theory (DFT) calculated molecular vibrational spectrum. Molecules were (C53H18), (C23H12) and (C12H8). Origin of DIB may come from the photoexcitation between molecular orbitals. For those molecules, we calculated excitation energy by the time dependent DFT. In case of (C53H18), mono cation shows calculated 722nm excitation band coincide well with observed DIB at 722.31nm, also calculated 693nm coincide with observed 693.90nm. Di-cation one also shows good coincidence by calculated 864nm with 864.82nm DIB. For middle sized molecule (C23H12), mono cation shows calculated 617nm coincidence with observed 617.73nm, also calculated 645nm with observed 645.16nm. Smaller sized di-cation molecule of (C12H8) show calculated band of 440nm roughly related to observed 442.89nm DIB. By this study, we could indicate the pentagon hexagon combined PAH would be promising candidate floating in interstellar space.