Astronomical Quantum-chemical Origin of Ubiquitously Observed Interstellar Infrared Spectrum due to Polycyclic Aromatic Hydrocarbon

TL;DR

This paper investigates the quantum-mechanical origins of the interstellar infrared spectrum attributed to PAHs, revealing how void-induced molecular structures and ionization states produce characteristic IR features observed in space.

Contribution

It introduces a quantum-mechanical explanation for interstellar PAH IR spectra, emphasizing void-induced structural changes and ionization effects on vibrational modes.

Findings

Void-induced PAH structures exhibit specific IR-active vibrational modes.

Cationic PAHs produce stronger IR emissions at key wavelengths compared to neutral forms.

Quantum structural changes explain the ubiquity of observed interstellar IR features.

Abstract

Interstellar infrared observation shows featured spectrum due to polycyclic aromatic hydrocarbon (PAH)at wavelength 3.3,6.2,7.6,7.8,8.6,and 11.3 micrometer,which are ubiquitously observed in many astronomical dust clouds and galaxies. Our previous first principles calculation revieled that viod induced coronene (C23H12)2+ and circumcoronene (C53H18)1+ could reproduce such spectrum very well. In this study, quantum-mechanic origin was studied through atomic configuration change and atomic vibration mode analysis. By a high speed particle attack, carbon void would be introduced in PAH. Molecular configuration was deformed by the Jahn-Teller quantum effect. Carbon SP3 local bond was created among SP2 graphene like carbon network. Also, carbon tetrahedron local structure was created. Such peculiar structure is the quantum origin. Those metamorphosed molecules would be photo-ionized by the central star strong photon irradiation resulting cation molecules. Atomic vibration mode of cation molecule (C23H12)2+ was compared with that of neutral one (C23H12). At 3.3 micrometer, both molecules show show C-H stretching mode and give fairly large infrared intensity. At 6.2,7.6,7.8, and 8.6 micrometer bands, cation molecule show complex C-C stretching and shrinking mixing modes and remain large infrared emission. Whereas, neutral molecule gives harmonic motion, which cancelles each other resulting very small infrared intensity. At 11.3 micrometer, both neutral and cation molecules show C-H bending motion perpendicular to a molecular plane, which contributes to strong emission. Actual observed spectrum would be a sum of such quantum-mechanic origined molecules.