2025
Permanent URI for this collectionhttps://dl.bhu.ac.in/bhuir/handle/123456789/62057
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PublicationArticle Investigating C−D out-of-plane vibrational modes in PAHs as a tool to study interstellar deuterium-containing PAHs(Oxford University Press, 2025) Mridusmita Buragohain; Takashi Onaka; Amit Pathak; Akant Vats; Itsuki SakonPrevious as well as recent observations by ISO, Spitzer, AKARI, SOFIA, JWST etc. have revealed various characteristics of midinfrared emission bands between 3 and 20 μm. Subsequently,severalforms of organicsincluding polycylic aromatic hydrocarbons (PAHs)/PAH-like molecules are proposed as carriers for these bands. Deuterated PAH (PAD) is one such substituted PAH, which is proposed as a potential candidate carrier for weak emission bands at 4.4 and 4.65 μm, detected towards few astronomical targets and are characteristics of aromatic and aliphatic C−D stretching modes in a PAD molecule, respectively. However, the 4.4 μm band is not widely detected. In order to validate PADs as carriers for mid-infrared emission bands, an additional alternative tool is crucial. If PAHs are deuterated, they should also possess an inherent signature from the C−D out-of-plane (C−Doop) vibrations, which are at the longer wavelength side. In this report, features due to C−Doop modes in PAHs bearing a single to multiple deuterium atoms are reported by performing quantum-chemical calculations. This paper reports that some of the C−Doop vibrations appear at the 14–19 μm range. Also, the strength of C−Doop modes is not proportional to the D/H ratio in PAHs. In addition, a moderate change in the spectra of deuterated PAHs is observed from that of the undeuterated counterparts, as deuteration would alternate the adjacency class of the C-H bonds and the mass distribution of the molecule. We discuss the efficiency and usefulness of these bands to constrain the form of PAHs emitting mid-infrared emission bands. © 2025 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society.