Nitrogen Substituted Polycyclic Aromatic Hydrocarbon As Capable Interstellar Infrared Spectrum Source Considering Astronomical Chemical Evolution Step To Biological Organic Purine And Adenine

TL;DR

This study uses density functional theory to analyze nitrogen-substituted polycyclic aromatic hydrocarbons, suggesting certain ionized forms could form in interstellar space and contribute to chemical evolution toward biological molecules like purine and adenine.

Contribution

It identifies specific nitrogen-substituted PAHs with IR spectra similar to astronomical observations, proposing their formation in space and their role in chemical evolution.

Findings

Nitrogen-substituted PAHs with one or two N atoms match astronomical IR spectra.

Higher N substitution (three or more N atoms) does not match observed spectra.

Biological organics like purine and adenine do not match interstellar IR spectra.

Abstract

In order to find out capable chemical evolution step from astronomically created organic in interstellar space to biological organic on the earth, infrared spectrum of nitrogen substituted carbon pentagon-hexagon coupled polycyclic aromatic hydrocarbon was analyzed by the density functional theory. Ionization was modeled from neutral to tri-cation. Among one nitrogen and two nitrogen substituted NPAH, we could find good examples showing similar IR behavior with astronomically well observed one as like C8H6N1, C7H5N2, and C7H5N2. We can imagine that such ionized NPAH may be created in interstellar space by attacks of high energy nitrogen and photon. Whereas, in case of three and four nitrogen substituted cases as like C6H4N3 and C5H3N4, there were no candidate showing similar behavior with observed one. Also, IR of typical biological organic with four and five nitrogen substituted one as like purine and adenine resulted no good similarity with observed one. By such theoretical comparison, one capable story of chemical evolution of PAH in interstellar space was that one and two nitrogen substituted carbon pentagon-hexagon molecules may have a potential to be created in interstellar space, whereas more than three nitrogen substituted molecules including biological organic purine and adenine may not be synthesized in space, possibly on the earth.