  In order to find out capable molecular source of astronomically well observed
infrared (IR) spectrum, asymmetric molecular configuration polycyclic aromatic
hydrocarbon (PAH) was analyzed by the density functional theory (DFT) analysis.
Starting molecules were benzene C6H6, naphthalene C10H8 and 1H-phenalene C13H9.
In interstellar space, those molecules will be attacked by high energy photon
and proton, which may bring cationic molecules as like C6H6n+ (n=0~3 in
calculation), C10H8n+, and C13H9n+, also CH lacked molecules C5H5n+, C9H7n+,
and C12H8n+. IR spectra of those molecules were analyzed based on DFT based
Gaussian program. Results suggested that symmetrical configuration molecules as
like benzene, naphthalene , 1H-phenalene and those cation ( +, 2+, and 3+) show
little resemblance with observed IR. Contrast to such symmetrical molecules,
several cases among cationic and asymmetric configuration molecules show fairly
good IR tendency. One typical example was C12H83+, of which calculated harmonic
IR wavelength were 3.2, 6.3, 7.5, 7.8, 8.7, 11.3, and 12.8 micro meter, which
correspond well to astronomically observed wavelength of 3.3, 6.2, 7.6, 7.8,
8.6, 11.2, and 12.7 micro meter. It was amazing agreement. Also, some cases
like C5H5+, C9H7+, C9H72+, C9H73+ and C12H82+ show fairly good coincidence.
Such results suggest that asymmetric and cationic PAH may be capable source of
interstellar dust.
