Document Type
Article
Publication Date
9-22-2026
Abstract
Interstellar aromatic infrared band (AIB) spectra show agreement with presently computed anharmonic spectra for various types of polycyclic aromatic hydrocarbons (PAHs) determined using a novel semiempirical quantum chemical method. Since the AIB spectrum is a blend of emission spectra from a vast number of different PAHs, likely with an array of different molecular structures, the spectra for a sample set of 31 PAHs ranging in size from naphthalene (C10H8) up to circumbiphenyl (C38H16) are combined, giving consideration to almost all PAH structural motifs. The computed numerical quartic force fields coupled to second-order vibrational perturbation theory support the claim that PAH C-H stretches are responsible for the features close to 3000 cm−1 (3.3 μm). The shoulder at 3080 cm−1 (3.24 μm) of this feature likely also arises from similar motions, notably in small PAHs. Additionally, the present work highlights that the mid-IR features of neutral PAH combination bands could be responsible for the bulk of the plateaus underlying the strong AIBs in the 2000–1000 and the 980–590 cm−1 (5–10 and 11–15 μm) ranges. Finally, low-frequency combination bands are also computed in the vicinity of the 5.25 μm feature and are consistent with the provenance of this feature hypothesized nearly 40 yr ago. PAHs of all classes are likely to contribute to different portions of interstellar spectra, but more anharmonic PAH spectra are needed to delineate this fully.
Recommended Citation
Nolan J. H. White et al 2026 ApJ 1009 113. https://doi.org/10.3847/1538-4357/ae9fed
Copyright
The authors
Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.
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Other Chemistry Commons, Physical Chemistry Commons, Stars, Interstellar Medium and the Galaxy Commons
Comments
This article was originally published in The Astrophysical Journal, volume 1009, in 2026. https://doi.org/10.3847/1538-4357/ae9fed