Time-dependent mass spectra and breakdown graphs. 18. pyrene

Ling, Yun; Gotkis, Yehiel; Lifshitz, Chava

doi:10.1255/ejms.158

Cited by 40 publications

(66 citation statements)

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“…), the activation energies for the H 2 -loss from a duo and a solo position are of 3.89 and 2.2 eV, respectively. Assuming a change in entropy of −53.1 J/K/mol (Ling et al 1995), we get that superhydrogenated molecules will preferably lose their extra H atom after UV photon absorption, rather than an H 2 molecule, and that superhydrogenated isomers with free C atoms are not relevant species. Thus, we do not consider direct H 2 -loss from superhydrogenated molecules.…”

Section: Photodissociation Channelsmentioning

confidence: 96%

“…For coronene and its dehydrogenated states (N H ≤ 12), we will use the activation energies and entropies derived for pyrene cation from the time-dependent mass spectrometry experiments of Ling et al (1995); that is, activation energies of 4.6 and 4.1 eV, and entropies of 44.8 and 55.6 J/K/mol, for PAHs with an even and odd number of H atoms, respectively (see Table 2). …”

Section: Photodissociation Channelsmentioning

confidence: 99%

“…N solo corresponds to the number of solo H atoms of each molecule, i.e., 0 for coronene, 6 for circumcoronene and 12 for circumcircumcoronene. Dissociation parameters for normal-todehydrogenated molecules are taken from Ling et al (1995). The activation energies considered for the H-loss from superhydrogenated molecules are taken from the theoretical work of .…”

Section: Photodissociation Channelsmentioning

confidence: 99%

“…These small differences do not have an impact on the derived rates. Given the lack of data, we will use an activation entropy of 55.6 J/K/mol, as assumed for PAHs with an odd number of H atoms (Ling et al 1995).…”

Section: Photodissociation Channelsmentioning

confidence: 99%

“…Experimental and theoretical studies on neutral PAHs with extra H atoms suggest PAHs could effectively form H 2 through Eley-Rideal abstractions (Bauschlicher 1998;Rauls & Hornekaer 2008;Thrower et al 2011;Mennella et al 2012). At the same time, PAHs could also contribute to the H 2 budget through photodissociation, where H 2 -loss competes with H-loss, the main fragmentation channel after photon excitation (e.g., Jochims et al 1994;Ling et al 1995). Boschman et al (2015) built a kinetic model based on the coronene molecule (24 carbon atoms), to study the role of PAHs in the formation of H 2 in PDRs.…”

Section: Introductionmentioning

confidence: 99%

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Hydrogenation and dehydrogenation of interstellar PAHs: Spectral characteristics and H₂formation

Andrews

Candian

Tielens

2016

A&A

117

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Context. We have modelled the abundance distribution and IR emission of the first 3 members of the coronene family in the north-west photodissociation region of the well-studied reflection nebulae NGC 7023. Aims. Our aim was 3-fold: i) analyze the distribution of abundances; (ii) examine the spectral footprints from the hydrogenation state of polycyclic aromatic hydrocarbons (PAHs); and (iii) assess the role of PAHs in the formation of H 2 in photodissociation regions. Methods. To model the physical conditions inside the cloud, we used the Meudon PDR Code, and we gave this as input to our kinetic model. We used specific molecular properties for each PAH, based on the latest data available at the present time. We considered the loss of an H atom or an H 2 molecule as multiphoton processes, and we worked under the premise that PAHs with extra H atoms can form H 2 through an Eley-Rideal abstraction mechanism. Results. In terms of abundances, we can distinguish clear differences with PAH size. The smallest PAH, coronene (C 24 H 12 ), is found to be easily destroyed down to the complete loss of all of its H atoms. The largest species circumcircumcoronene (C 96 H 24 ), is found in its normal hydrogenated state. The intermediate size molecule, circumcoronene (C 54 H 18 ), shows an intermediate behaviour with respect to the other two, where partial dehydrogenation is observed inside the cloud. Regarding spectral variations, we find that the emission spectra in NGC 7023 are dominated by the variation in the ionization of the dominant hydrogenation state of each species at each point inside the cloud. It is difficult to "catch" the effect of dehydrogenation in the emitted PAH spectra since, for any conditions, only PAHs within a narrow size range will be susceptible to dehydrogenation, being quickly stripped off of all H atoms (and may isomerize to cages or fullerenes). The 3 µm region is the most sensitive one towards the hydrogenation level of PAHs. Conclusions. Based on our results, we conclude that PAHs with extra H atoms are not the carriers of the 3.4 µm band observed in NGC 7023, since these species are only found in very benign environments. Finally, concerning the role of PAHs in the formation of H 2 in photodissociation regions, we find that H 2 abstraction from PAHs with extra H atoms is an inefficient process compared to grains. Instead, we propose that photodissociation of PAHs of small-to-intermediate sizes could contribute to H 2 formation in PDR surfaces, but they cannot account by themselves for the inferred high H 2 formation rates in these regions.

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Section: Photodissociation Channelsmentioning

confidence: 96%

Section: Photodissociation Channelsmentioning

confidence: 99%

Section: Photodissociation Channelsmentioning

confidence: 99%

Section: Photodissociation Channelsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Hydrogenation and dehydrogenation of interstellar PAHs: Spectral characteristics and H₂formation

Andrews

Candian

Tielens

2016

A&A

117

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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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Plasmon excitation in polycyclic aromatic hydrocarbons studied by photoionization

Ling

Lifshitz

1996

Chemical Physics Letters

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Time-dependent mass spectra and breakdown graphs. 18. pyrene

Cited by 40 publications

References 0 publications

Hydrogenation and dehydrogenation of interstellar PAHs: Spectral characteristics and H₂formation

Hydrogenation and dehydrogenation of interstellar PAHs: Spectral characteristics and H₂formation

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

Plasmon excitation in polycyclic aromatic hydrocarbons studied by photoionization

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Time-dependent mass spectra and breakdown graphs. 18. pyrene

Cited by 40 publications

References 0 publications

Hydrogenation and dehydrogenation of interstellar PAHs: Spectral characteristics and H2formation

Hydrogenation and dehydrogenation of interstellar PAHs: Spectral characteristics and H2formation

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

Plasmon excitation in polycyclic aromatic hydrocarbons studied by photoionization

Contact Info

Product

Resources

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Hydrogenation and dehydrogenation of interstellar PAHs: Spectral characteristics and H₂formation

Hydrogenation and dehydrogenation of interstellar PAHs: Spectral characteristics and H₂formation

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