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Interstellar ubiquitous infrared spectrum (IR) due to polycyclic aromatichydrocarbon (PAH) was observed in many astronomical dust clouds. A capableastronomical chemical evolution path from graphene to PAH was studied based onthe first principles calculation. Step 1 is a nucleation of nano-carbon aftersupernova by super-cooling at expanding helium sphere. As a typical model,graphene molecule (C )24 having coronene skeleton with seven carbon hexagonswas tried.Step 2 is a proton sputtering and passivation on ejected graphenemolecule. Slow speed proton with energy less than 4.3eV makes hydrogenation,Graphene molecule (C )24 was transformed to PAH (C24H12). Higher speed protonhaving sufficient energy larger than 18.3 eV could make a void in a molecule aslike C23H12. Resulted structure was a combination of two carbon pentagons andfive hexagons. Step 3 is photo-ionization of those molecules by high energyphoton. Electrons are removed to make a molecule to cation. Model molecule(C23H12) became mono-cation (C23H12)+, di-cation (C23H12)2+ and so on. Typicalenergy difference between such cation was 6.5 and 10.8 eV. If the light sourcehas a nature of black-body radiation, effective temperature will be 18000K ~24000K, which suggested that central light source star may have 4 to 7 timesheavier than our sun. Finally, theoretical IR spectrum was obtained. Especiallyin case of (C23H12)2+, calculated emission spectrum revealed that among 13major peaks, 11 peaks could correlate with ubiquitous observed IR one.

Astronomical chemical evolution from graphene to polycyclic aromatic hydrocarbon reproducing observed infrared spectrum