Multiply charged naphthalene and its C10H8 isomers: bonding, spectroscopy and implications in AGN environments

Abstract

Naphthalene (C10H8) is the simplest polycyclic aromatic hydrocarbon (PAH) and an important component in a series of astrochemical reactions involving hydrocarbons. Its molecular charge state affects the stability of its isomeric structures, which is specially relevant in ionised astrophysical environments. We thus perform an extensive computational search for low-energy molecular structures of neutral, singly, and multiply charged naphthalene and its isomers with charge states +q = 0-4 and investigate their geometric properties and bonding situations. We find that isomerisation reactions should be frequent for higher charged states and that open chains dominate their low-energy structures. We compute both the scaled-harmonic and anharmonic infrared spectra of selected low-energy species and provide the calculated scaling factors for the naphthalene neutral, cation, and dication global minima. All simulated spectra reproduce satisfactorily the experimental data and, thus, are adequate for aiding observations. Moreover, the potential presence of these species in the emission spectra of the circumnuclear regions of active galactic nuclei (AGNs), with high energetic X-ray photon fluxes, is explored using the experimental value of the naphthalene photodissociation cross-section, σ_{ph-d}, to determine its half-life, t_{1/2}, at a photon energy of 2.5 keV in a set of relevant sources. Finally, we show that the computed IR bands of the triply and quadruply charged species are able to reproduce some features of the selected AGN sources.

arXiv commentAccepted for publication in the Monthly Notices of the Royal Astronomical Society. 15 pages, 7 pages, supplementary information available online

References in corpus (36)

• Infrared Emission from Interstellar Dust. II. The Diffuse Interstellar Medium
• Intrinsic atomic orbitals: An unbiased bridge between quantum theory and chemical concepts
• Revisiting the Unified Model of Active Galactic Nuclei
• Infrared Emission from Interstellar Dust. I. Stochastic Heating of Small Grains
• The rich 6 to 9 um spectrum of interstellar PAHs
• Detection of the Aromatic Molecule Benzonitrile ($c$-C${}_6$H${}_5$CN) in the Interstellar Medium
• Detection of Two Interstellar Polycyclic Aromatic Hydrocarbons via Spectral Matched Filtering
• A subarcsecond resolution near-infrared study of Seyfert and `normal' galaxies: II. Morphology
• Pure hydrocarbon cycles in TMC-1: Discovery of ethynyl cyclopropenylidene, cyclopentadiene and indene
• Variations of the Mid-IR Aromatic Features Inside and Among Galaxies
• Discovery of the Pure Polycyclic Aromatic Hydrocarbon Indene ($c$-C${}_9$H${}_8$) with GOTHAM Observations of TMC-1
• The Infrared Nuclear Emission of Seyfert Galaxies on Parsec Scales: Testing the Clumpy Torus models
• Discovery of benzyne, o-C6H4, in TMC-1 with the QUIJOTE line survey
• Models of Chemistry, Thermal Balance and Infrared Spectra from Intermediate-Aged Disks around G and K stars
• The Excitation of Extended Red Emission: New Constraints on its Carrier From HST Observations of NGC 7023
• AGN-Starburst connection in NGC7582: Gemini near-infrared spectrograph integral field unit observations
• Benzonitrile as a proxy for benzene in the cold ISM: low temperature rate coefficients for CN + C${}_6$H${}_6$
• Probing the size and charge of Polycyclic Aromatic Hydrocarbons
• Laboratory Photo-chemistry of PAHs: Ionization versus Fragmentation
• An atlas of mid-infrared spectra of star-forming and active galaxies
• The 15-20 um emission in the reflection nebula NGC2023
• PAH features within few hundred parsecs of active galactic nuclei
• Interstellar Detection of 2-Cyanocyclopentadiene, C${}_5$H${}_5$CN, a Second Five-Membered Ring Toward TMC-1
• Polycyclic Aromatic Hydrocarbon and Emission Line Ratios in Active Galactic Nuclei and Starburst Galaxies
• High Spatial Resolution Mid-infrared Observations of Three Seyfert Galaxies
• ALMA Observations of the Submillimeter Dense Molecular Gas Tracers in the Luminous Type-1 Active Nucleus of NGC 7469
• Astrochemical relevance of VUV ionization of large PAH cations
• Mid-Infrared Spectroscopic Evidence for AGN Heating Warm Molecular Gas
• Laboratory gas-phase infrared spectra of two astronomically relevant PAH cations: diindenoperylene, C${}_{32}$H${}_{16}$${}^{+}$ and dicoronylene, C${}_{48}$H${}_{20}$${}^{+}$
• Cold molecular gas and PAH emission in Seyfert galaxies
• Infrared Spectra of Hexa-peri-hexabenzocoronene Cations:HBC+ and HBC2+
• Destruction and multiple ionization of PAHs by X-rays in circumnuclear regions of AGNs
• The relationship between X-ray and optical absorbers in active galactic nuclei
• Single and Double Photoionization and Photodissociation of Toluene by Soft X-rays in Circumstellar Environment
• Infrared action spectroscopy of doubly charged PAHs and their contribution to the aromatic infrared bands
• Profile comparison of the 6-9 $\mu$m polycyclic aromatic hydrocarbon bands in starburst-dominated galaxies