Understanding dehydrogenation sequence in fluorene+ by multiphoton ionisation-excitation processes

Vinitha, M. V.; Nair, Arya M.; Ramanathan, Karthick; Kadhane, U.

doi:10.1016/j.ijms.2021.116704

Cited by 3 publications

(4 citation statements)

References 30 publications

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“…Since a single XUV photon has enough energy to cause ionization and/or hydrogen dissociation, the production of the fluorenyl cation is observed to be more intense during XUV interaction than in the case of Vis pulse interaction that needs multiple photons to produce the fluorenyl cation. Low abundance of the fluorenyl cation is consistent to the observation in other studies with rather low ~4.1 eV photon energy [62] and proton impact studies [19] A more prominent C 2 H + x peak is observed in the XUV-only case compared to the Vis-only condition. During interaction with XUV photons, both the parent monocation and the dication can dissociate to produce C 2 H +…”

Section: Ionization and Fragmentation Of Flusupporting

confidence: 90%

Fragmentation Dynamics of Fluorene Explored Using Ultrafast XUV-Vis Pump-Probe Spectroscopy

et al. 2022

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We report on the use of extreme ultraviolet (XUV, 30.3 nm) radiation from the Free-electron LASer in Hamburg (FLASH) and visible (Vis, 405 nm) photons from an optical laser to investigate the relaxation and fragmentation dynamics of fluorene ions. The ultrashort laser pulses allow to resolve the molecular processes occurring on the femtosecond timescales. Fluorene is a prototypical small polycyclic aromatic hydrocarbon (PAH). Through their infrared emission signature, PAHs have been shown to be ubiquitous in the universe, and they are assumed to play an important role in the chemistry of the interstellar medium. Our experiments track the ionization and dissociative ionization products of fluorene through time-of-flight mass spectrometry and velocity-map imaging. Multiple processes involved in the formation of each of the fragment ions are disentangled through analysis of the ion images. The relaxation lifetimes of the excited fluorene monocation and dication obtained through the fragment formation channels are reported to be in the range of a few tens of femtoseconds to a few picoseconds.

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Section: Ionization and Fragmentation Of Flusupporting

confidence: 90%

Fragmentation Dynamics of Fluorene Explored Using Ultrafast XUV-Vis Pump-Probe Spectroscopy

et al. 2022

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“…In the past, hydrogen migrations have been known to precede sequential and molecular hydrogen losses. [36][37][38] In the current study, we see that hydrogen migration plays a role in the loss of larger neutrals too. In the case of the mass 129 isomers, the ring expansion to the seven member isomerizations starts with hydrogen migrations to the tertiary carbon.…”

Section: Discussionsupporting

confidence: 56%

“…35 Even in processes that appear relatively simple like neutral hydrogen losses, where at first glance, one might expect that only direct bond fission of the C-H bond to play a role, hydrogen migrations leading to various C-H shifted isomers were found to precede the hydrogen dissociation channels. [36][37][38] These isomerization mechanisms have persistently appeared in different theoretical studies too [39][40][41] and possibly hint toward a universal behavior 42 behind the dissociation of this family of PA(N)Hs. However, the dynamical details of these mechanisms are not directly decipherable from most experimental spectra.…”

Section: Introductionmentioning

confidence: 87%

In search of universalities in the dissociative photoionization of PANHs via isomerizations

Ramanathan,

Selvaraj

et al. 2023

The Journal of Chemical Physics

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In search of the cause behind the similarities often seen in the fragmentation of PANHs, vacuum ultraviolet (VUV) photodissociation of two pairs of isomers quinoline–isoquinoline and 2-naphthylamine-3-methyl-quinoline are studied using the velocity map imaging technique. The internal energy dependence of all primary fragmentation channels is obtained for all four target molecules. The decay dynamics of the four molecules is studied by comparing their various experimental signatures. The dominant channel for the first pair of isomers is found to be hydrogen cyanide (HCN) neutral loss, while the second pair of isomers lose HCNH neutral as its dominant channel. Despite this difference in their primary decay products and the differences in the structures of the four targets, various similarities in their experimental signatures are found, which could be explained by isomerization mechanisms to common structures. The fundamental role of these isomerization in controlling different dissociative channels is explored via a detailed analysis of the experimental photoelectron–photoion coincidences and the investigation of the theoretical potential energy surface. These results add to the notion of a universal PANH fragmentation mechanism and suggests the seven member isomerization as a key candidate for this universal mechanism. The balance between isomerization, dissociation, and other key mechanistic processes in the reaction pathways, such as hydrogen migrations, is also highlighted for the four molecules.

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“…The DFT functional and basis set used in this study are widely used by experimentalists and theoreticians to computationally model small PAH fragmentation [16,41,[47][48][49][50] and are sufficiently fast to calculate all the necessary 611 species in this study. Occasionally, however, DFT methods are known to fail to produce accurate reaction energies, [51,52] isomerisation energies [53] or even qualitatively describe textbook reaction pathways.…”

Section: Species Propertiesmentioning

confidence: 99%

Competition between Loss of H₂ versus H+H in the Fragmentation of the Fluorene Cation

Désesquelles,

Domin,

et al. 2023

ChemPhysChem

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The fluorene cation is a frequently studied molecule in the context of fragmentation experiments. This is because of its potential role in interstellar chemistry, notably as a precursor of PAH cages. In this paper, we analyze H, H+, H2 and H+2 losses from the fluorene cation using the SMF (Statistical Molecular Fragmentation) model. We calculate the probabilities of all the 534 possible fragmentation channels as a function of the excitation energy, up to the loss of three hydrogens. Four different types of hydrogen atom pairings (from the same carbon, from the same ring, from different rings and across‐the‐bay) have been tested in order to determine which types contribute to the actual production of hydrogen molecules. The simulated breakdown curves are in very good agreement with different experimental results when same ring pairing is taken into account. It was possible to deduce from the model the locations of the emitted H, H+, H2 and H+2 species.

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Understanding dehydrogenation sequence in fluorene+ by multiphoton ionisation-excitation processes

Cited by 3 publications

References 30 publications

Fragmentation Dynamics of Fluorene Explored Using Ultrafast XUV-Vis Pump-Probe Spectroscopy

Fragmentation Dynamics of Fluorene Explored Using Ultrafast XUV-Vis Pump-Probe Spectroscopy

In search of universalities in the dissociative photoionization of PANHs via isomerizations

Competition between Loss of H₂ versus H+H in the Fragmentation of the Fluorene Cation

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Understanding dehydrogenation sequence in fluorene+ by multiphoton ionisation-excitation processes

Cited by 3 publications

References 30 publications

Fragmentation Dynamics of Fluorene Explored Using Ultrafast XUV-Vis Pump-Probe Spectroscopy

Fragmentation Dynamics of Fluorene Explored Using Ultrafast XUV-Vis Pump-Probe Spectroscopy

In search of universalities in the dissociative photoionization of PANHs via isomerizations

Competition between Loss of H2 versus H+H in the Fragmentation of the Fluorene Cation

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Competition between Loss of H₂ versus H+H in the Fragmentation of the Fluorene Cation