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It is well known since 2010 that fullerene C60 is widespread through theinterstellar space. Also, it is well known that graphene is a source materialfor synthesizing fullerene. Here, we simply assume the occurrence of graphenein space. Infrared spectra of graphene molecules are calculated to compare bothto astronomical observational spectra and to laboratory experimental one. Modelmolecules for DFT calculation are selected by one astronomical assumption, thatis, single void in charge neutral graphene of C13, C24 and C54, resulting C12,C23 and C53. They have a carbon pentagon ring within a hexagon network.Different void positions are classified as different species. Single void issurrounded by 3 radical carbons, holding 6 spins. Spin state affects molecularconfiguration and vibrational spectrum. It was a surprise that the tripletstate is stable than the singlet. Most of charge neutral and triplet spin statespecies show closely resembling spectra with observed one of carbon richplanetary nebulae Tc1 and Lin49. We could assign major bands at 18.9micrometer, and sub-bands at 6.6, 7.0, 7.6, 8.1, 8.5, 9.0 and 17.4 micrometer.It is interesting that those graphene species were also assigned in thelaboratory experiments on laser-induced carbon plasma, which are analogies ofcarbon cluster creation in space. The conclusion is that graphene moleculescould potentially contribute to the infrared emission bands of carbon-richplanetary nebulae.

Graphene Molecules Contributing to the Infrared Bands of Carbon Rich Planetary Nebulae