  Infrared spectrum (IR) of Herbig Ae young stars was reproduced and classified
by hydrocarbon pentagon-hexagon combined molecules by the quantum chemical
calculation. Observed IR list by B. Acke et al. was categorized to four
classes. Among 53 Herbig Ae stars, 26 samples show featured IR pattern named
Type-D, which shows common IR peaks at 6.2, 8.3, 9.2, 10.0, 11.3, 12.1, and
14.0 micrometer. Typical star is HD144432. Calculation on di-cation molecule
(C12H8)2+ having hydrocarbon one pentagon and two hexagons shows best
coincidence at 6.1, 8.2, 9.2, 9.9, 11.3, 12.2, and 14.1 micrometer. There are
some variation in Type-D. Spectrum of HD37357 was explained by a mixture with
di-cation (C12H8)2+ and tri-cation (C12H8)3+. Ubiquitously observed spectrum
Type-B was observed in 12 samples of Acke's list. In case of HD85567, observed
16 peaks were precisely reproduced by a single molecule (C23H12)2+. There is a
mixture case with Type-B and Type-D. Typical example was HD142527. In this
study, we could identify hidden carrier molecules for all types of IR in Herbig
Ae stars.
