Article
Astronomy & Astrophysics
Ameek Sidhu, Els Peeters, Jan Cami, Collin Knight
Summary: The study utilizes PCA analysis on the variations of PAH emission features in the reflection nebula NGC 2023, finding that 99% of the variations can be explained by two principal components, representing the emission amount of ionized PAH mixtures and changes in the ionization state of PAHs.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2021)
Article
Astronomy & Astrophysics
Ameek Sidhu, Josh Bazely, Els Peeters, Jan Cami
Summary: PCA analysis was conducted on the fluxes of five PAH bands in the reflection nebula NGC 7023. The results showed that two principal components explained most of the observed variance in PAH fluxes. The first component represented total PAH emission while the second component was related to the ionization state of the PAHs. The analysis also revealed the presence of two subsets of ionized bands in the PDR but not in the cavity.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
Carla M. Canelo, Dinalva A. Sales, Amancio C. S. Friaca, Miriani Pastoriza, Karin Menendez-Delmestre
Summary: This study analyzed the 7.7 and 8.6 micron PAH bands in starburst-dominated galaxies and classified them into different Peeters' classes. The analysis showed a potential cosmological evolution in the molecular nature of PAHs in these galaxies, with B class objects being more frequent at higher redshifts. Further studies are needed to address this trend.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2021)
Article
Astronomy & Astrophysics
U. Jacovella, Jack T. Buntine, Mariah Cotter, Giel Muller, Michael S. Scholz, Emmanuel Dartois
Summary: This study assesses the potential of oxygenated carbon chain ions as explanations for diffuse interstellar bands using density-functional theory and coupled cluster single-double and perturbative triple theory. The results show that the linear structures of these ions are the most stable and their optical absorptions mainly occur in the visible or near-infrared spectral regions. However, based on the known data, the growth rate of O-bearing carbon chains via ion-neutral reaction mechanisms is too low to account for the diffuse interstellar bands.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
Venkata Lakshmi Karri, Sumalya Kaluva, Ajay Chaudhari, Takashi Onaka, Mahadevappa Naganathappa
Summary: This paper discusses the infrared features of C-24 based on density functional theory calculation and suggests that some features observed in celestial objects may be attributed to C-24. The electronic absorption spectra of C-24 isomers are calculated and compared with the bump feature at 217 nm in the interstellar extinction curve. Four groups of C-24 isomers, namely cage, planar, bowl, and ring forms, are considered in neutral and charged states. The study reveals significant changes in infrared and electronic absorption spectra, as well as structural parameters, upon ionization.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
Yang Yang, Yao Wang, Zhibo Jiang, Zhiwei Chen
Summary: The study focuses on understanding the initial stages of star formation through investigating the physical and chemical properties of gas infall motion in molecular clumps. The FTS wide-sideband mode of the IRAM 30-m telescope was used to observe nine infall sources with significant double-peaked blue line profiles. Molecular line data was obtained, and multiple molecules and isotopic transition lines were identified in these sources. Chemical simulations were used to fit the observed molecular abundances, indicating that most sources are in the early HMPO stage with temperatures around several 10 K.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
M. Roellig, V Ossenkopf-Okada
Summary: Numerical models of photodissociation regions (PDRs) play a crucial role in understanding massive star forming regions through simulations. The Cologne KOSMA-tau PDR model stands out as a sophisticated model utilizing a spherical cloud geometry, allowing for the simulation of clumpy PDRs. The study presents advancements in chemical solution methods, surface chemistry formulation, and ice mantle structure changes in PDRs, showcasing the potential for enhanced line emission and interpretation of ALMA observations.
ASTRONOMY & ASTROPHYSICS
(2022)
Article
Astronomy & Astrophysics
Congcong Zhang, Xiaoyi Hu, Yuanyuan Yang, Yang Chen, Junfeng Zhen, Liping Qin
Summary: In this study, the ion-molecule collision reaction between fullerene and polycyclic aromatic hydrocarbon (PAH) molecules was investigated. The dominant reaction channels were determined to be charge transfer and molecular adduct formation channels, depending on the specific fullerene and PAH system. Quantum calculations were used to investigate the observed reaction behaviors, and the binding effect of the CH2 unit in the PAH molecule was identified as the main factor influencing the reaction outcomes. These findings provide valuable insights into the physical-chemical processes between fullerene and PAH molecules.
ASTRONOMY & ASTROPHYSICS
(2022)
Article
Astronomy & Astrophysics
Gael Rouille, Serge A. Krasnokutski, Yvain Carpentier
Summary: By analyzing archival spectra and literature data, the evaluation of the C-60:C-60(+) ratio in interstellar clouds is proposed. The results suggest that the fraction of neutral molecules in these clouds may be notable, despite the lack of detection of expected vibronic bands. Further research and improved laboratory data are needed for certainty.
ASTRONOMY & ASTROPHYSICS
(2021)
Article
Astronomy & Astrophysics
Susana Iglesias-Groth
Summary: We used Spitzer Space Telescope spectra to search for the aromatic amino acid tryptophan in the interstellar gas of the young star cluster IC 348. We found emission lines in the observed spectrum that are consistent with the laboratory measurements of tryptophan. The presence of these lines in multiple interstellar locations suggests that the molecule causing the emission is widespread in interstellar space.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
Ameek Sidhu, A. G. G. M. Tielens, Els Peeters, Jan Cami
Summary: This article presents a charge distribution based model for calculating the infrared spectrum of polycyclic aromatic hydrocarbon (PAH) molecules. By simulating a sample of well-studied photodissociation regions (PDRs) with known physical conditions, it is found that the proportion of charged ions varies in different environments, and the observations are consistent with the model's predictions, demonstrating that changes in charge state can account for variations in PAH emission.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
Luis Alvarez-Thon, Timothy J. Lee, Ryan C. Fortenberry, Natalia Inostroza-Pino
Summary: This study calculates the aromaticity of cyclic hydrocarbon molecules using the ring current strength (RCS) value, aiming to predict their detectability in astrophysical media. Known interstellar molecules exhibit high RCS values, while those with low or negative values have not yet been observed, indicating the significance of this metric in astrophysical studies.
ASTRONOMY & ASTROPHYSICS
(2022)
Article
Astronomy & Astrophysics
Athena R. Flint, Alexandria G. Watrous, Brent R. Westbrook, Dev J. Patel, Ryan C. Fortenberry
Summary: This study characterizes three derivatives in the dense interstellar medium, namely c-C-3(C2H)(2), c-C-3(CN)(2), and c-C-3(C2H)(CN), and establishes their potential for astrophysical observation. The results show that c-C-3(C2H)(2) and c-C-3(C2H)(CN) are viable candidates for detection, while c-C-3(CN)(2) is unlikely to be directly observable due to its small dipole moment.
ASTRONOMY & ASTROPHYSICS
(2023)
Article
Astronomy & Astrophysics
Ameek Sidhu, A. G. G. M. Tielens, Els Peeters, Jan Cami
Summary: We propose a model based on charge distribution to calculate the infrared spectrum of fullerenes. Our analysis shows that the relative intensity of specific features in the spectrum can be used to determine the charge state of fullerenes in interstellar spectra. We further simulate the emission from polycyclic aromatic hydrocarbons (PAHs) and fullerenes in a reflection nebula, and find that the derived gamma values for fullerenes are significantly lower than those for PAHs.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
B. Kerkeni, I Garcia-Bernete, D. Rigopoulou, D. P. Tew, P. F. Roche, D. C. Clary
Summary: In this study, we extend the prediction of vibrational spectra to large-sized polycyclic aromatic hydrocarbon (PAH) molecules using various computational chemistry methodologies. The impact of PAH size on vibrational band positions is investigated through global optimizations and frequency calculations. A general Frequency Scaling Function (FSF) is developed to shift the bands and provide a systematic comparison. The emergence of new features in large PAHs and changes in the intensity of certain features are observed. Trends in the PAH band ratio as a function of radiation intensity are also explored.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
Hassan Sabbah, Mickael Carlos, Peter Jenniskens, Muawia H. Shaddad, Jean Duprat, Cyrena A. Goodrich, Christine Joblin
Summary: The first firm detection of fullerenes, including C-30 to C-100, in the Almahata Sitta meteorite provides strong evidence for the existence of fullerenes in meteorites. The origin of these fullerenes is different from other molecular families found in the same samples, indicating that they may be an intrinsic component of an unidentified carbon phase.
ASTROPHYSICAL JOURNAL
(2022)
Article
Physics, Atomic, Molecular & Chemical
Gabi Wenzel, Aude Simon, Shreyak Banhatti, Pavol Jusko, Stephan Schlemmer, Sandra Bruenken, Christine Joblin
Summary: Cationic benzylium and tropylium isomers are competitive in the dehydrogenation process of methylated polycyclic aromatic hydrocarbon cations. The compactness of the precursor plays a crucial role in determining the isomer distribution. The XCH(2)(+) species might explain the 6.2 μm aromatic infrared band observed in astrophysical environments.
JOURNAL OF MOLECULAR SPECTROSCOPY
(2022)
Article
Chemistry, Physical
Sebastien Zamith, Ali Kassem, Jean-Marc L'hermite, Christine Joblin
Summary: Measurement and analysis of water molecule attachment rates on cationic pyrene clusters have shown a strong dependence on size and collision energy, with a model based on Langevin-type collision rate being used to rationalize the results and extrapolate them to conditions encountered in astrophysical environments.
JOURNAL OF PHYSICAL CHEMISTRY A
(2022)
Article
Astronomy & Astrophysics
O. Lacinbala, F. Calvo, E. Dartois, C. Falvo, P. Parneix, A. Simon, T. Pino
Summary: The study investigates the recurrent fluorescence of carbon clusters induced by stellar photon absorption and its ability to explain the near-IR emission observed in reflection nebulae and planetary nebulae. The modelling results suggest that C-60 cages and flakes, as well as C-42 cages, can account for the observed continuum emission. The carriers contain about 0.1-1.5% of the interstellar carbon abundance.
ASTRONOMY & ASTROPHYSICS
(2023)
Article
Astronomy & Astrophysics
Clement Dubosq, Paula Pla, Emmanuel Dartois, Aude Simon
Summary: This study investigates the influence of hydrogenation rate on the mid-infrared spectra of carbon clusters and provides constraints on the abundance of carbon in the interstellar medium. The study also suggests that these carbon clusters may contribute to the extinction curve and the UV bump.
ASTRONOMY & ASTROPHYSICS
(2023)
Article
Chemistry, Physical
Gustavo A. Garcia, Leo Dontot, Mathias Rapacioli, Fernand Spiegelman, Philippe Brechignac, Laurent Nahon, Christine Joblin
Summary: A study on the dissociative ionisation of clusters of pyrene is presented, combining experimental and theoretical approaches. Experimental appearance energies of the fragments formed from neutral monomer loss were measured in the photon energy range of 7.2-12.0 eV for clusters up to the hexamer, showing a deviation from statistical dissociation. Electronic structure calculations suggest the importance of considering excited states in interpreting experimental results, even in relatively large systems. Non-statistical effects in the dissociative ionization process of polycyclic aromatic hydrocarbon (PAH) clusters may impact the assessment of their stability in astrophysical environments.
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
(2023)
Article
Chemistry, Physical
H. Leboucher, A. Simon, M. Rapacioli
Summary: In this study, we investigate the energetic and structural properties of clusters composed of polycyclic aromatic hydrocarbon and water monomers using density-functional-based tight-binding potential. The binding energies and dissociation channels are discussed, revealing stronger cohesion energies for water clusters interacting with a pyrene dimer compared to pure water clusters. Furthermore, the interaction with a pyrene dimer affects the magic numbers of water clusters, and the charge distribution in cations is mainly carried by the pyrene molecules.
JOURNAL OF CHEMICAL PHYSICS
(2023)
Article
Multidisciplinary Sciences
L. Velilla-Prieto, J. P. Fonfria, M. Agundez, A. Castro-Carrizo, M. Guelin, G. Quintana-Lacaci, I. Cherchneff, C. Joblin, M. C. McCarthy, J. A. Martin-Gago, J. Cernicharo
Summary: Research has found that during the thermally pulsing phase of asymptotic giant branch (AGB) stars, extended dusty envelopes and inhomogeneous molecular gas structures are formed. High-resolution observations have revealed large convective cells near stars like IRC+10 degrees 216, which interact with pulsation to shape the surrounding circumstellar environment.
Article
Chemistry, Physical
Nicolas Cinq, Aude Simon, Fernand Louisnard, Jerome Cuny
Summary: This work improves the description of liquid water in the self-consistent-charge density-functional based tight-binding scheme by using Weighted Mulliken charges and optimizing the O-H repulsive potential through the iterative Boltzmann inversion process. The newly developed models are validated by considering various properties. The combination of WMull charges and the optimized O-H repulsive potential offers a good compromise to study the dynamic properties and chemistry of liquid water at a quantum chemical level.
JOURNAL OF PHYSICAL CHEMISTRY B
(2023)
Article
Chemistry, Physical
Nadia Ben Amor, Salimata Konate, Aude Simon
Summary: This study investigates the photo-reactivity of polycyclic aromatic hydrocarbons (PAHs) with water molecules and in water ice under low energy photon irradiation. It reveals the role of charge transfer states PAH(+)-H2O- and explores the electronic excited states of planar and bowl-shaped PAHs, such as pyrene and corannulene, interacting with water clusters. The results suggest that pyrene exhibits efficient reactivity with water in water ice due to low energy excitations from p orbitals to diffuse orbitals located on water molecules, while corannulene lacks reactivity with water in a noble gas matrix.
THEORETICAL CHEMISTRY ACCOUNTS
(2023)
Article
Chemistry, Physical
Daniel B. Rap, Aude Simon, Kim Steenbakkers, Johanna G. M. Schrauwen, Britta Redlich, Sandra Brunken
Summary: The cationic fragmentation products of pyridine and benzonitrile in dissociative ionization were studied through infrared action spectroscopy. The experimental vibrational fingerprints of the dominant cationic fragments were compared with quantum chemical calculations, revealing diverse molecular fragment structures. Potential energy surfaces were calculated using the determined structures of the cationic fragments, shedding light on the nature of the neutral fragment partner. The different fragmentation pathways observed in pyridine and benzonitrile have implications in astrochemistry.
FARADAY DISCUSSIONS
(2023)
Article
Optics
Ozan Lacinbala, Florent Calvo, Cyril Falvo, Pascal Parneix, Mathias Rapacioli, Aude Simon, Thomas Pino
Summary: The experimental results of the emission spectrum of hot C60 reveal a broad and continuous spectrum, which contradicts the discrete and narrow absorption spectrum of buckminsterfullerene with high symmetry. By computationally modeling the emission spectrum of isolated carbon clusters, we propose a broad distribution of isomers that are likely present under experimental conditions. The model successfully predicts a blackbody-like emission spectrum, except for a quantitative shift in the maximum peak.
Article
Chemistry, Physical
Sebastien Zamith, Ali Kassem, Jean-Marc L'Hermite, Christine Joblin, Jerome Cuny
Summary: This study reports on threshold collision induced dissociation experiments on protonated water clusters at low temperature. The dissociation energies of the clusters show a specific trend around n = 21 and n = 22, which is in agreement with theoretical predictions.
JOURNAL OF CHEMICAL PHYSICS
(2023)
Article
Chemistry, Physical
Shreyak Banhatti, Daniel B. Rap, Aude Simon, Heloise Leboucher, Gabi Wenzel, Christine Joblin, Britta Redlich, Stephan Schlemmer, Sandra Bruenken
Summary: Polycyclic aromatic hydrocarbons (PAHs) are important components in astrophysical environments and are responsible for the aromatic infrared bands observed in galactic and extra-galactic spectra. PAHs can grow even at low temperatures and can be fragmented by UV photons, providing an alternative route for the formation of complex hydrocarbons in UV-rich interstellar regions. In this study, by analyzing the IR spectra of fragment ions formed from the dissociation of anthracene and phenanthrene molecules, the dominant structure of the fragment ion was identified to be the acenaphthylene cation. Molecular dynamics simulations further clarified the fragmentation process. These findings highlight the importance of species containing a pentagonal ring in the photochemistry of small PAHs.
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
(2022)