  Protoplanetary disk around a just born young star contains a lot of cosmic
dust. especially polycyclic-aromatic-hydrocarbon (PAH), which would become
basic component to create biological organics. This study classified many
astronomically observed infrared spectra of protoplanetary disks to three
typical spectra. Type-A show well known astronomical bands of 6.2, 7.8, 8.6 and
11.3 micrometer. Whereas Type-B included unknown complex bands. Type-(A+B) was
their mixed type. We tried to find specific molecule by Density Functional
Theory (DFT) calculation. We found that Type-A could be explained by large PAH
molecules of (C$_{23}$H$_{12}$) and (C$_{53}$H$_{18}$), which are
hexagon-pentagon combined molecular structure. Background molecule of Type-B
was smaller ones of (c-C$_3$H$_2$), (C$_5$H$_5$), (C$_9$H$_7$) and
(C$_{12}$H$_8$). Type-(A+B) was reproduced well by mixing those molecules of A
and B. Astronomical detailed observation shows that central star of Type-A has
larger mass and higher temperature than that of Type-B. This suggests that at
very early stage of our solar system, our protoplanetary disk had been made up
by Type-B molecules. It was interesting that (C$_5$H$_5$) and (C$_9$H$_7$) of
Type-B molecules has similar molecular structure with biological nucleic-acid
on our earth. Type-B molecules was supposed to become the template for
synthesizing biological organics and finally for creating our life.
