Infrared Spectroscopy of Pentagon-Containing PAHs: Indenyl and Fluorenyl Anions and Indenyl Cation
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arXiv
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| Auteurs principaux: | , , , , , , |
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| Format: | Preprint |
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2025
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| _version_ | 1866916683278450688 |
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| author | Wenzel, Gabi Jiménez-Redondo, Miguel Ončák, Milan McGuire, Brett A. Brünken, Sandra Caselli, Paola Jusko, Pavol |
| author_facet | Wenzel, Gabi Jiménez-Redondo, Miguel Ončák, Milan McGuire, Brett A. Brünken, Sandra Caselli, Paola Jusko, Pavol |
| contents | Polycyclic aromatic hydrocarbon (PAH) ions are crucial intermediates in interstellar chemistry and may play a key role in the infrared emission features observed in space. Here, we investigate the infrared spectra of the indenyl (C$_9$H$_7^-$) and fluorenyl (C$_{13}$H$_9^-$) anions and the indenyl cation (C$_9$H$_7^+$) using infrared pre-dissociation (IRPD) spectroscopy. The experiments were performed in a cryogenic 22 pole ion trap at the FELion beamline of the tunable free-electron laser FELIX. Spectral analysis of the two anionic PAHs, in combination with density functional theory (DFT) computations, revealed key vibrational modes near 1300 cm$^{-1}$, making these ions potential carriers of the 7.7 μm PAH emission band seen in many astronomical objects. The feature-rich spectrum of cationic indenyl could not be entirely explained by modeling through time-independent anharmonic DFT calculations. Although a better match has been achieved through molecular dynamics simulations, we cannot completely rule out the presence of multiple cationic isomers of the H-loss fragments of indene in the experiments. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2504_07512 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Infrared Spectroscopy of Pentagon-Containing PAHs: Indenyl and Fluorenyl Anions and Indenyl Cation Wenzel, Gabi Jiménez-Redondo, Miguel Ončák, Milan McGuire, Brett A. Brünken, Sandra Caselli, Paola Jusko, Pavol Astrophysics of Galaxies Polycyclic aromatic hydrocarbon (PAH) ions are crucial intermediates in interstellar chemistry and may play a key role in the infrared emission features observed in space. Here, we investigate the infrared spectra of the indenyl (C$_9$H$_7^-$) and fluorenyl (C$_{13}$H$_9^-$) anions and the indenyl cation (C$_9$H$_7^+$) using infrared pre-dissociation (IRPD) spectroscopy. The experiments were performed in a cryogenic 22 pole ion trap at the FELion beamline of the tunable free-electron laser FELIX. Spectral analysis of the two anionic PAHs, in combination with density functional theory (DFT) computations, revealed key vibrational modes near 1300 cm$^{-1}$, making these ions potential carriers of the 7.7 μm PAH emission band seen in many astronomical objects. The feature-rich spectrum of cationic indenyl could not be entirely explained by modeling through time-independent anharmonic DFT calculations. Although a better match has been achieved through molecular dynamics simulations, we cannot completely rule out the presence of multiple cationic isomers of the H-loss fragments of indene in the experiments. |
| title | Infrared Spectroscopy of Pentagon-Containing PAHs: Indenyl and Fluorenyl Anions and Indenyl Cation |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2504.07512 |