Infrared spectra of methyl-, and nitrogen-modified void coronene; modeling a carrier of interstellar polycyclic aromatic hydrocarbon

TL;DR

This study models modified void coronene molecules with methyl and nitrogen substitutions to better match astronomical infrared spectra, revealing how these modifications influence spectral features and potentially identify carriers of interstellar PAHs.

Contribution

It introduces specific methyl and nitrogen modifications to void coronene, improving spectral match with astronomical observations and elucidating vibrational modes involved.

Findings

Methyl modification increases 11.4 micron peak intensity to 70-90%.

Nitrogen substitution at peripheral sites yields 60% peak height and good spectral reproduction.

Vibration analysis links 11.3 micron mode to C-H out-of-plane bending, with nitrogen acting as an vibrational anchor.

Abstract

Void induced coronene C23H12++ was suggested to be a possible carrier of the astronomically observed polycyclic aromatic hydrocarbon (PAH), which shows unique molecular structure with carbon two pentagons connected with five hexagons. Well observed astronomical infrared spectrum from 3-15 micron could be almost reproduced based on density functional theory. However, there remain several discrepancies with observed spectra, especially on 11-15 micron band weaker intensity. Observed 11.2 micron intensity is comparable to 7.6-7.8 micron one. Methyl-modified molecule C24H14++ revealed that calculated peak height of 11.4 micron show fairly large intensity up to 70-90% compared with that of 7.6-7.8 micron band. Also, nitrogen atom was substituted to peripheral C-H site of void coronene to be C22H11N1++. Pentagon site substituted case show 60% peak height. This molecule also reproduced well 12-15 micron peak position and relative intensity. Vibration mode analysis demonstrated that 11.3 micron mode comes from C-H out of plane bending. Heavy nitrogen plays as like an anchor role for molecule vibration.