Mid-infrared vibrational study of deuterium-containing PAH variants

TL;DR

This study uses density functional theory to analyze the infrared properties of deuterium-containing PAH molecules, aiming to connect molecular features with interstellar deuterium observations.

Contribution

It provides the first detailed theoretical infrared spectra of various deuterium-substituted PAHs, enhancing understanding of their role in interstellar chemistry.

Findings

Calculated D/H ratios align with observational data

Identified specific IR features of deuterated PAHs

Supported PAHs as reservoirs of interstellar deuterium

Abstract

Polycyclic Aromatic Hydrocarbon (PAH) molecules have been long proposed to be a major carrier of 'Unidentified Infrared' (UIR) emission bands that have been observed ubiquitously in various astrophysical environments. These molecules can potentially be an efficient reservoir of deuterium. Once the infrared properties of the deuterium- containing PAHs are well understood both experimentally and theoretically, the interstellar UIR bands can be used as a valuable tool to infer the cause of the deuterium depletion in the ISM. Density Functional Theory (DFT) calculations have been carried out on deuterium-containing ovalene variants to study the infrared properties of these molecules. These include deuterated ovalene, cationic deuterated ovalene, deuteronated ovalene and deuterated-deuteronated ovalene. We present a D/H ratio calculated from our theoretical study to compare with the observationally proposed D/H ratio.