Leiden University Scholarly Publications

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Lemmens, A.K.; Rap, D.B.; Thunnissen, J.M.M.; Gruet, S.; Steber, A.L.; Panchagnula, S.; ... ; Rijs, A.M. (2020)

Far-IR absorption of neutral polycyclic aromatic hydrocarbons (PAHs): light on the mechanism of IR–UV ion dip spectroscopy

Article / Letter to editor
Gas-phase IR–UV double-resonance laser spectroscopy is an IR absorption technique that bridges the gap between experimental IR spectroscopy and theory. The IR experiments are used to directly evaluate predicted frequencies and potential energy surfaces as well as to probe the structure of isolated molecules. However, a detailed understanding of the underlying mechanisms is, especially in the far-IR regime, still far from complete, even though this is crucial for properly interpreting the recorded IR absorption spectra. Here, events occurring upon excitation to vibrational levels of polycyclic aromatic hydrocarbons by far-IR radiation from the FELIX free electron laser are followed using resonance-enhanced multiphoton ionization spectroscopy. These studies provide detailed insight into how ladder climbing and anharmonicity influence IR–UV spectroscopy and therefore the resulting IR signatures in the far-IR region. Moreover, the potential energy surfaces of these low-frequency...Show moreGas-phase IR–UV double-resonance laser spectroscopy is an IR absorption technique that bridges the gap between experimental IR spectroscopy and theory. The IR experiments are used to directly evaluate predicted frequencies and potential energy surfaces as well as to probe the structure of isolated molecules. However, a detailed understanding of the underlying mechanisms is, especially in the far-IR regime, still far from complete, even though this is crucial for properly interpreting the recorded IR absorption spectra. Here, events occurring upon excitation to vibrational levels of polycyclic aromatic hydrocarbons by far-IR radiation from the FELIX free electron laser are followed using resonance-enhanced multiphoton ionization spectroscopy. These studies provide detailed insight into how ladder climbing and anharmonicity influence IR–UV spectroscopy and therefore the resulting IR signatures in the far-IR region. Moreover, the potential energy surfaces of these low-frequency delocalized modes are investigated and shown to have a strong harmonic character.
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All authors
Lemmens, A.K.; Rap, D.B.; Thunnissen, J.M.M.; Gruet, S.; Steber, A.L.; Panchagnula, S.; Tielens, A.G.G.M.; Schnell, M.; Jan Buma, W.; Rijs, A.M.
Date
2020-10-09
Journal
Journal of Physical Chemistry Letters
Volume
11
Issue
21
Pages
8997–9002
DOI
doi:10.1021/acs.jpclett.0c02714