Vibrational mode analysis of void induced coronene as a possible carrier of the astronomical aromatic infrared bands

TL;DR

This study investigates void-induced coronene di-cation as a potential carrier of astronomical aromatic infrared bands, using density functional theory to analyze vibrational modes and compare with observed spectra.

Contribution

It provides a detailed vibrational mode analysis of void-induced coronene di-cation and links its infrared spectrum to astronomical observations, suggesting it as a PAH carrier.

Findings

Infrared spectrum of C23H12++ closely matches astronomical sources.

Vibrational modes correspond to observed IR emission peaks.

Molecular deformation due to Jahn-Teller effect confirmed.

Abstract

Void induced di-cation coronene C23H12++ is a possible carrier of the astronomically observed polycyclic aromatic hydrocarbon (PAH). Based on density functional theory, multiple spin state analysis was done for neutral void coronene C23H12. Singlet spin state was most stable (lowest total energy). By the Jahn-Teller effect, there occurs serious molecular deformation. Point group D6h of pure coronene transformed to C2 symmetry having carbon two pentagons. Advanced singlet stable molecules were di-cation C23H12++ and di-anion C23H12- -. Molecular configuration was almost similar with neutral C23H12. However, electric dipole moment of these two charged molecules show reversed direction with 1.19 and 2.63 Debey. Calculated infrared spectrum of C23H12++ show a very likeness to observed one of two astronomical sources of HD44179 and NGC7027. Harmonic vibrational mode analysis was done for C23H12++. At 3.2 micrometer, C-H stretching at pentagons was featured. From 6.4 to 8.7 micrometer, C-C stretching mode was observed. In-plane-bending of C-H was in a range of 7.6-9.2 micrometer. Both C-H out-of plane bending and C-C stretching were accompanied from 11.4 to 14.3 micrometer. Astronomically observed emission peaks of 3.3, 6.2, 7.6, 7.8, 8.6, 11.2, 12.7, 13.5 and 14.3 micrometer were compared well with calculated peaks of 3.2, 6.5, 7.6, 7.8, 8.6, 11.4, 12.9, 13.5, and 14.4 micrometer.