Void defect induced magnetism and structure change of carbon material-3, Polycyclic aromatic hydrocarbon

TL;DR

This study investigates how void defects and hydrogenation in polycyclic aromatic hydrocarbons (PAHs) influence their structure, magnetism, and infrared spectra, linking molecular changes to astronomical observations of space phenomena.

Contribution

It reveals that void defects and hydrogenation alter PAH structures and magnetic properties, and correlates specific PAH molecules with observed infrared spectra in space.

Findings

Void defects cause significant structural changes in PAHs.

Hydrogenation diminishes magnetism by forming SP3 bonds.

Calculated infrared bands match astronomical observations.

Abstract

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.