The High-Resolution Far- to Near-Infrared Anharmonic Absorption Spectra of Cyano-Substituted Polycyclic Aromatic Hydrocarbons from 300-6200 cm−1
Cyano-substituted polycyclic aromatic hydrocarbons (CN-PAHs) may contribute to the emission detected in the 7 – 9 μm (1430 – 1100 cm−1) and 11 – 15 μm (900 – 670 cm−1) regions of astronomical IR spectra. Anharmonic quantum chemical computations of 17 CN-PAH isomers for 4 small PAHs and Benzene reveal strong, broad absorption features across the entire 300 – 6200 cm−1 (33 – 1.6 μm) frequency range.
In particular, when a FWHM of 15 cm−1 is applied, the composite CN-PAH spectrum is almost indistinguishable from the unsubstituted-PAH spectrum. At high resolution, however, the infrared absorption spectra reveal unique, identifiable features of CN-PAHs in the 700 – 950, 1100 – 1300, 2000 – 2500, and 3400 – 3600 cm−1 ranges.
The in-plane and out-of-plane CH bending vibrational frequencies of CN-PAHs are shifted when comparing isomers and to their unsubstituted counterparts, making their differentiation in mixed laboratory experiments possible. The overall aromatic CH stretch fundamental (2950 – 3200 cm−1) and first overtone (5950 – 6200 cm−1) regions are relatively unaffected by the cyano-substitution, with changes only to the breadth and intensity of the bands.
Detailed spectroscopic data on the normal mode components of each state reported herein provide the means to directly assign future laboratory spectra and to guide direct IR observations of astronomical regions with, e.g., JWST.
Composite anharmonic absorption spectra from 3400 – 4800 cm−1 , the CN stretch first overtone and combination band region, for all isomers of each molecule including the (a) one isomer of cyanobenzene, (b) two isomers of cyanonaphthalene, (c) three isomers of cyanoanthracene, (d) three isomers of cyanopyrene, and (e) five isomers of cyanophenanthrene. — astro-ph.GA
Vincent J. Esposito, Ryan C. Fortenberry, Christiaan Boersma, Louis J. Allamandola
Comments: Submitted to ACS Earth and Space Chemistry
Subjects: Astrophysics of Galaxies (astro-ph.GA); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:2406.00088 [astro-ph.GA] (or arXiv:2406.00088v1 [astro-ph.GA] for this version)
https://doi.org/10.48550/arXiv.2406.00088
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Submission history
From: Vincent Esposito
[v1] Fri, 31 May 2024 16:14:14 UTC (15,111 KB)
https://arxiv.org/abs/2406.00088
Astrobiology, Astrochemistry,
