The spectrum of NGC 7027 from 3080 to 2630 wavenumbers (3.25-3.80 microns) - Detection of new atomic and molecular hydrogen lines and new constraints on the chemical sidegroups on polycyclic aromatic hydrocarbons

1991 ◽  
Vol 376 ◽  
pp. 599 ◽  
Author(s):  
Scott A. Sandford
Keyword(s):  
Polycyclic Aromatic Hydrocarbons ◽  
Aromatic Hydrocarbons ◽  
Molecular Hydrogen ◽  
Ngc 7027 ◽  
Polycyclic Aromatic ◽  
Hydrogen Lines

Physisorption of Molecular Hydrogen on Polycyclic Aromatic Hydrocarbons:  A Theoretical Study

2002 ◽  
Vol 106 (34) ◽  
pp. 8689-8696 ◽  
Author(s):  
Fabien Tran ◽  
Jacques Weber ◽  
Tomasz A. Wesołowski ◽  
Frikia Cheikh ◽  
Yves Ellinger ◽  
...  
Keyword(s):  
Polycyclic Aromatic Hydrocarbons ◽  
Aromatic Hydrocarbons ◽  
Molecular Hydrogen ◽  
Theoretical Study ◽  
Polycyclic Aromatic

Polycyclic aromatic hydrocarbons – catalysts for molecular hydrogen formation

2014 ◽  
Vol 168 ◽  
pp. 223-234 ◽  
Author(s):  
A. L. Skov ◽  
J. D. Thrower ◽  
L. Hornekær
Keyword(s):  
Polycyclic Aromatic Hydrocarbons ◽  
Cross Section ◽  
Cross Sections ◽  
Aromatic Hydrocarbons ◽  
Molecular Hydrogen ◽  
Mass Spectrometry Data ◽  
Quadrupole Mass ◽  
Hydrogen Formation ◽  
Polycyclic Aromatic ◽  
Peak Mass

Polycyclic aromatic hydrocarbons (PAHs) have been shown to catalyse molecular hydrogen formation. The process occurs via atomic hydrogen addition reactions leading to the formation of super-hydrogenated PAH species, followed by molecular hydrogen forming abstraction reactions. Here, we combine quadrupole mass spectrometry data with kinetic simulations to follow the addition of deuterium atoms to the PAH molecule coronene. When exposed to sufficiently large D atom fluences, coronene is observed to be driven towards the completely deuterated state (C24D36) with the mass distribution peaking at 358 amu, just below the peak mass of 360 amu. Kinetic models reproduce the experimental observations for an abstraction cross-section of σabs = 0.01 Å2 per excess H/D atom, and addition cross-sections in the range of σadd = 0.55–2.0 Å2 for all degrees of hydrogenation. These findings indicate that the cross-section for addition does not scale with the number of sites available for addition on the molecule, but rather has a fairly constant value over a large interval of super-hydrogenation levels.

scholarly journals Probing the size and charge of polycyclic aromatic hydrocarbons

2020 ◽  
Vol 494 (1) ◽  
pp. 642-664 ◽  
Author(s):  
A Maragkoudakis ◽  
E Peeters ◽  
A Ricca
Keyword(s):  
Polycyclic Aromatic Hydrocarbons ◽  
Aromatic Hydrocarbons ◽  
Intensity Ratio ◽  
Emission Spectra ◽  
Infrared Emission ◽  
Radiation Fields ◽  
Ionization Fraction ◽  
Ngc 7027 ◽  
Out Of Plane ◽  
Polycyclic Aromatic

ABSTRACT We present a new method to accurately describe the ionization fraction and the size distribution of polycyclic aromatic hydrocarbons (PAHs) within astrophysical sources. To this purpose, we have computed the mid-infrared emission spectra of 308 PAH molecules of varying sizes, symmetries, and compactness, generated in a range of radiation fields. We show that the intensity ratio of the solo CH out-of-plane bending mode in PAH cations and anions (referred to as the ‘11.0’ μm band, falling in the 11.0–11.3 μm region for cations and anions) to their 3.3 μm emission scales with PAH size, similarly to the scaling of the 11.2/3.3 ratio with the number of carbon atoms (NC) for neutral molecules. Among the different PAH emission bands, it is the 3.3 μm band intensity that has the strongest correlation with NC, and drives the reported PAH intensity ratio correlations with NC for both neutral and ionized PAHs. The 6.2/7.7 intensity ratio, previously adopted to track PAH size, shows no evident scaling with NC in our large sample. We define a new diagnostic grid space to probe PAH charge and size, using the (11.2 + 11.0)/7.7 and (11.2 + 11.0)/3.3 PAH intensity ratios, respectively. We demonstrate the application of the (11.2 + 11.0)/7.7–(11.2 + 11.0)/3.3 diagnostic grid for galaxies M82 and NGC 253, for the planetary nebula NGC 7027, and the reflection nebulae NGC 2023 and NGC 7023. Finally, we provide quantitative relations for PAH size determination depending on the ionization fraction of the PAHs and the radiation field they are exposed to.

Sign in / Sign up

Export Citation Format

Share Document