Dissociative single and double photoionization of biphenyl (C12H10) by soft X-rays in planetary nebulae

2020 ◽  
Vol 499 (4) ◽  
pp. 6066-6083
Author(s):  
Heidy M Quitián-Lara ◽  
Felipe Fantuzzi ◽  
Ricardo R Oliveira ◽  
Marco A C Nascimento ◽  
Wania Wolff ◽  
...  

ABSTRACT Biphenyl (C12H10), or phenylbenzene, is an important building block of polycyclic aromatic hydrocarbons (PAHs), whose infrared spectral features are present in a variety of galactic and extragalactic sources. In this work, we use synchrotron radiation coupled with time-of-flight spectrometry to study the photoionization and photodissociation processes of biphenyl upon its interaction with soft X-ray photons at energies around the inner-shell C1s resonance. These results are compared with our previous studies with benzene (C6H6) and naphthalene (C10H8), and discussed in the context of four planetary nebulae featuring PAH infrared emission: BD+30○3639, NGC 7027, NGC 5315, and NGC 40. We show that the mass spectrum of biphenyl before the C1s resonance energy is dominated by single photoionization processes leading to C6H$_{5}^+$, C6H$_{4}\, ^{+\cdot}$, and C12H$_{10}\, ^{+\cdot}$, while after the resonance dissociation following multiple photoionization processes is dominant. The release of neutral C6H6 and C6H$_{5}\, ^\cdot$ species accounts for one of the most relevant dissociation processes starting from the doubly ionized biphenyl, indicating that heterolytic charge separation of the two phenyl rings is also achieved. By using quantum chemical calculations, we show that the biphenylic structure is a high-lying isomer of the singly and doubly ionized C12H10 species, whose minimum energy geometries are related to the acenaphthene molecule, composed of a C2-bridged naphthalene. Furthermore, we estimate the lifetime of biphenyl for 275 and 310 eV in photon-dominated regions of planetary nebulae. We discuss distinct processes that may enhance its lifetime and those of other small-sized PAHs in such astrophysical environments.

1978 ◽  
Vol 76 ◽  
pp. 103-110 ◽  
Author(s):  
David M Rank

The discovery of infrared continuum emission from NGC 7027 by Gillett, Low, and Stein in 1967 marked the beginning of far infrared observations of planetary nebulae. These early observations verified the predictions (Delmer, Gould, and Ramsey 1967) of infrared fine structure line emission from the SIV ion and also provided a surprise; namely, that the continuum radiation from planetary nebulae was not free-free emission from the gas, but rather that it was thermal emission from heated dust grains. In the ten years which have elapsed since 1967, numerous infrared emission lines have been observed and interpreted in many of the brighter planetary nebulae. In the middle infrared these lines were principally Ne II at 12.8μ, Gillett et al. (1969); SIV at 10.5μ, Holtz, et al. (1971), Gillett, et al. (1972), Aitken and Jones (1973); and AIII at 9.0μ Geballe and Rank (1973) and Gillett and Forrest (1973).


1992 ◽  
Vol 150 ◽  
pp. 333-334
Author(s):  
V. Escalante ◽  
A. Sternberg ◽  
A. Dalgarno

Detailed calculations are reported of the intensities of the near infrared forbidden lines of neutral carbon atoms at λ 985.0 nm, 982.3 nm and 872.7 nm emitted from dense clouds subjected to intense radiation fields. The metastable levels that produce the lines are excited by radiative recombination of the C+ ions produced by photoionization. Impacts of electrons with C atoms in the heated edge zones of the clouds contribute an insignificant part to the excitation. The lines observed in M42 and NGC 2024 can be interpreted as arising in gas with densities in excess of 105 cm−3 and radiation fields with intensities between 103 and 106 times the average interstellar field intensity. Radiative recombination of C+ ions may also be an important source of the emission lines detected in the planetary nebulae NGC 6270 and NGC 7027.


2011 ◽  
Vol 7 (S283) ◽  
pp. 462-463
Author(s):  
Ryou Ohsawa ◽  
Takashi Onaka ◽  
Itsuki Sakon ◽  
Issei Yamamura ◽  
Mikako Matsuura ◽  
...  

AbstractWe investigate the infrared emission bands from Polycyclic Aromatic Hydrocarbons (PAHs) in Galactic planetary nebulae (PNe). PAHs in PNe are assumed to be in transition from circumstellar to interstellar PAHs. We select 15 evolved PNe taking account of effective stellar temperatures and obtain infrared spectra of PNe from AKARI (2.5–5 μm) and Spitzer (5–14 μm) observations. Their evolutionary phase is estimated using [SIV]10.51/[NeII]12.81. We find that the near-infrared PAH bands are significantly enhanced along with stellar evolution sequence. We also find that the ratio of 3.4 to 3.3 μm bands is enhanced. The enhancement might indicate some chemical processing, such as hydrogenation, on small PAHs.


1994 ◽  
Vol 146 ◽  
pp. 134-148 ◽  
Author(s):  
Alain Omont

The aim of this review is to discuss our knowledge on molecules in the circumstellar environment of evolved stars. In particular the presence and the behaviour of various kinds of molecules with several or many carbon atoms, in relation to C-rich dust, is considered.Such objects include mainly: (i) circumstellar shells of AGB carbon stars, either visible (such as Y CVn) or infrared (such as IRC+10216 (CW Leo)); (ii) planetary nebulae (PNe, e.g. NGC 7027); (iii) pre-planetary nebulae (PPNe, also called post-AGB stars, such as CRL 2688 or the Red Rectangle), probably in an intermediate evolution stage between the two former classes. I will not discuss more peculiar classes, such as R CrB stars and novae, for which very little is known about the presence of such molecular species.


2020 ◽  
Vol 494 (1) ◽  
pp. 642-664 ◽  
Author(s):  
A Maragkoudakis ◽  
E Peeters ◽  
A Ricca

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.


1989 ◽  
Vol 63 (15) ◽  
pp. 1629-1632 ◽  
Author(s):  
J. Arthur ◽  
G. S. Brown ◽  
D. E. Brown ◽  
S. L. Ruby

Author(s):  
Jan H. Kwapisz ◽  
Leszek Z. Stolarczyk

AbstractThe equilibrium carbon-carbon (C-C) bond lengths in π-electron hydrocarbons are very sensitive to the electronic ground-state characteristic. In the recent two papers by Stolarczyk and Krygowski (J Phys Org Chem, 34:e4154,e4153, 2021) a simple quantum approach, the Augmented Hückel Molecular Orbital (AugHMO) model, is proposed for the qualitative, as well as quantitative, study of this phenomenon. The simplest realization of the AugHMO model is the Hückel-Su-Schrieffer-Heeger (HSSH) method, in which the resonance integral β of the HMO model is a linear function the bond length. In the present paper, the HSSH method is applied in a study of C-C bond lengths in a set of 34 selected polycyclic aromatic hydrocarbons (PAHs). This is exactly the set of molecules analyzed by Riegel and Müllen (J Phys Org Chem, 23:315, 2010) in the context of their electronic-excitation spectra. These PAHs have been obtained by chemical synthesis, but in most cases no diffraction data (by X-rays or neutrons) of sufficient quality is available to provide us with their geometry. On the other hand, these PAHs are rather big (up to 96 carbon atoms), and ab initio methods of quantum chemistry are too expensive for a reliable geometry optimization. That makes the HSSH method a very attractive alternative. Our HSSH calculations uncover a modular architecture of certain classes of PAHs. For the studied molecules (and their fragments – modules), we calculate the values of the aromaticity index HOMA.


2003 ◽  
Vol 589 (1) ◽  
pp. 439-443 ◽  
Author(s):  
Holly L. Maness ◽  
Saeqa D. Vrtilek ◽  
Joel H. Kastner ◽  
Noam Soker

2012 ◽  
Vol 10 (H16) ◽  
pp. 699-700 ◽  
Author(s):  
Christine Joblin

AbstractWhen referring to unidentified infrared emission features, one has in mind the series of aromatic IR bands (AIBs) between 3.3 and 15 μm that are observed in emission in many environments where UV photons irradiate interstellar matter. These bands are now used by astronomers to classify objects and characterize local physical conditions. However, a deep analysis cannot proceed without understanding the properties of the band carriers. Large polycyclic aromatic hydrocarbon molecules are attractive candidates but interstellar species are still poorly characterized. Various studies emphasize the need for tackling the link between molecular aromatic species, aliphatic material and very small carbonaceous grains. Other unidentified emission features such as the 6.9, 21 and 30 μm bands could be involved in the evolutionary scenario.


2011 ◽  
Vol 7 (S283) ◽  
pp. 340-341 ◽  
Author(s):  
Ashkbiz Danehkar ◽  
David J. Frew ◽  
Quentin A. Parker ◽  
Orsola De Marco

AbstractWe estimate distances to the spherical planetary nebula Abell 39 and the bipolar planetary nebula NGC 7027 by interpolating from a wide grid of photoionization models using the 3-D code, MOCASSIN. We find preliminary distances of 1.5 kpc and 0.9 kpc respectively, with uncertainties of about 30%.


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