Anharmonic vibrational spectroscopy of Polycyclic Aromatic Hydrocarbons (PAHs)

Abstract

While powerful techniques exist to accurately account for anharmonicity in vibrational molecular spectroscopy, they are computationally very expensive and cannot be routinely employed for large species and/or at non- zero vibrational temperatures. Motivated by the study of Polycyclic Aromatic Hydrocarbon (PAH) emission in space, we developed a new code, which takes into account all modes and can describe all IR transitions including bands becoming active due to resonances as well as overtones, combination and difference bands. In this article, we describe the methodology that was implemented and discuss how the main difficulties were overcome, so as to keep the problem tractable. Benchmarking with high-level calculations was performed on a small molecule. We carried out specific convergence tests on two prototypical PAHs, pyrene (C${}_{16}$H${}_{10}$) and coronene (C${}_{24}$H${}_{12}$), aiming at optimising tunable parameters to achieve both acceptable accuracy and computational costs for this class of molecules. We then report the results obtained at 0 K for pyrene and coronene, comparing the calculated spectra with available experimental data. The theoretical band positions were found to be significantly improved compared to harmonic Density Functional Theory (DFT) calculations. The band intensities are in reasonable agreement with experiments, the main limitation being the accuracy of the underlying calculations of the quartic force field. This is a first step towards calculating moderately high-temperature spectra of PAHs and other similarly rigid molecules using Monte Carlo sampling.

arXiv commentaccepted for publication on Journal of Chemical Physics

References in corpus (6)

• ExoMol: molecular line lists for exoplanet and other atmospheres
• On-line database of the spectral properties of polycyclic aromatic hydrocarbons
• The aromatic infrared bands as seen by ISO-SWS: probing the PAH model
• Time-dependent density functional study of the electronic spectra of oligoacenes in the charge states -1, 0, +1, and +2
• High-resolution IR absorption spectroscopy of polycyclic aromatic hydrocarbons: the realm of anharmonicity
• ExoMol molecular line lists: XI The spectrum of nitric acid

Cited by in corpus (7)

• Anharmonic Infrared Spectra of Thermally Excited Pyrene(C${}_{16}$H${}_{10}$): the combined view of DFT-based GVPT2 with AnharmonicCaOs and approximate DFT molecular dynamics with DemonNano
• The Infrared Absorption Spectrum of Phenylacetylene and its Deuterated Isotopologue in the Mid- to Far-IR
• The High-Resolution Far- to Near-Infrared Anharmonic Absorption Spectra of Cyano-Substituted Polycyclic Aromatic Hydrocarbons from 300-6200 cm${}^{-1}$
• Experimental Approach to the Study of Anharmonicity in the Infrared Spectrum of Pyrene from 14 to 723 K
• The 3.3 $\mu$m Infrared Emission Feature: Observational and Laboratory Constraints on Its Carrier
• Anharmonic infrared spectra of cationic pyrene and superhydrogenated derivatives
• Extracting vibrational anharmonicities from short driven molecular dynamics trajectories