Void defect induced magnetism and structure change of carbon material-3,
  Polycyclic aromatic hydrocarbon
  Void-defect induced magnetism of graphene molecule was recently reported in
our previous paper of this series study. This paper investigated the case of
hydrogenated graphene molecule, in chemical term, polycyclic aromatic
hydrocarbon (PAH). Molecular infrared spectrum obtained by density functional
theory was compared with astronomical observation. Void-defect on PAH caused
serious structure change. Typical example of C23H12 had two carbon pentagon
rings among hexagon networks. Stable spin state was non-magnetic singlet state.
This is contrary to pure carbon case of C23, which show magnetic triplet state.
It was discussed that Hydrogen played an important role to diminish magnetism
by creating an SP3-bond among SP2-networks. Such a structure change affected
molecular vibration and finally to photoemission spectrum in infrared region.
The dication-C23H12 showed featured bands at 3.2, 6.3, 7.7, 8.6, 11.2, and 12.7
micrometer. It was surprising that those calculated bands coincided well with
astronomically observed bands in many planetary nebulae. To confirm our study,
large size molecule of C53H18 was studied. Calculation reproduced again similar
astronomical bands. Also, small size molecule of C12H8 showed good coincidence
with the spectrum observed for young stars. This paper would be the first
report to indicate the specific PAH in space.
