  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 recent 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.
