Oxygenated PAHs (OPAHs) in astrophysical environments Peter Sarre and D.M Rogers School of Chemistry, University of Nottingham, UK Polycyclic aromatic hydrocarbons (PAHs) are a significant component of the interstellar medium and of comets, interplanetary dust particles and meteorites [1,2]. Infrared spectra of PAHs and nitrogen-containing PAHs have been studied in some detail, but oxygenated forms (OPAHs) have received relatively little attention despite their likely importance in prebiotic chemistry. The advent of JWST is enabling infrared spectra to be obtained with high spectral and spatial resolution which will likely include features due to OPAHs. We report results of Density Functional Theory (DFT) calculations of vibrational spectra of oxygen-containing PAHs (OPAHs) with reference to astronomical infrared emission known as the `Aromatic Infrared Bands' (AIBs). Neutral and singly ionised PAHs with oxygen-containing chemical groups are considered - carbonyls and epoxides/ethers. Typical OPAHs studied here are oxygenated forms of coronene with extension to larger OPAHs. The DFT computations were performed using Q-Chem 5.0 [3], with the B3LYP hybrid exchange-correlation functional [4,5] and the 6-31G(d) basis set [6-8] to describe H, C and O atoms. Geometry optimisation followed by analytic harmonic vibrational frequency calculation was carried out to predict their infrared spectra. Previous theoretical studies of vibrational spectra of neutral OPAHs have been undertaken [9-11] but almost all in a materials rather than an astronomical context. The computed infrared spectra are compared with astronomical spectra of the Red Rectangle nebula - a known carbon-oxygen ‘mixed-chemistry' environment, and other nebulae including NGC 2023 and NGC 7023. From our results it is confirmed that a 6.0 µm astronomical emission band can be assigned to a C=O group on the PAH edge, and an 8 µm emission ‘bump' attributed to C-O-C ether groups. Our study also relates closely to laboratory and theoretical research on monolayer graphene oxide and oxygen/ PAH chemistry. In particular, a widely observed but unassigned broad astronomical optical feature, 'Extended Red Emission - ERE', has been attributed to graphene oxide (GO) nanoparticles [12] which are expected to share IR characteristics with OPAHs. In macroscopic GO samples laboratory infrared absorption at 6.0 and 8.0 µm is seen [13] as is ERE-like emission from laser-excited oxygenated graphene [14]. Given that carbonaceous chondrite meteorites also exhibit ERE-like optical emission [15], it will be of interest to explore more generally the role of OPAHs in the interstellar-planetary connection. References 1. Tielens A. G. G. M., 2013, Rev. Mod. Phys., 85, 1021 2. Tielens A. G. G. M., 2008, ARA&;A, 46, 289
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