scholarly journals Laboratory Studies on the Role of PAHs as DIB Carriers

2013 ◽  
Vol 9 (S297) ◽  
pp. 265-275
Author(s):  
F. Huisken ◽  
G. Rouillé ◽  
M. Steglich ◽  
Y. Carpentier ◽  
C. Jäger ◽  
...  
Keyword(s):  
Gas Phase ◽  
Cross Sections ◽  
Molecular Beam ◽  
Electronic Spectroscopy ◽  
Laboratory Studies ◽  
Diffuse Interstellar Bands ◽  
Matrix Isolation Spectroscopy ◽  
Laboratory Results ◽  
Polycyclic Aromatic

AbstractThe electronic spectroscopy of various polycyclic aromatic hydrocarbon (PAH) molecules has been studied in the laboratory at low temperatures using both molecular beam and matrix isolation spectroscopy techniques. While molecular beam spectra can be readily compared to astronomical observations, the band positions measured in Ne and Ar matrices are extrapolated to obtain rather good estimates for the same transitions in the gas phase. Absolute absorption cross sections are determined for gas-phase and matrix spectra by comparing them with calibrated solution spectra. All laboratory results are analyzed and discussed in view of the role that PAHs can play as carriers of the diffuse interstellar bands (DIBs). Our studies suggest that regular neutral PAHs are not responsible for any of the known strong DIBs.

scholarly journals Polyacenes and diffuse interstellar bands

2019 ◽  
Vol 625 ◽  
pp. A41 ◽  
Author(s):  
A. Omont ◽  
H. F. Bettinger ◽  
C. Tönshoff
Keyword(s):  
Gas Phase ◽  
Current Knowledge ◽  
Visible Range ◽  
High Symmetry ◽  
Carbon Chains ◽  
Diffuse Interstellar Bands ◽  
Carbon Compounds ◽  
Laboratory Results ◽  
Polycyclic Aromatic ◽  
Recent Laboratory

The identification of the carriers of the diffuse interstellar bands (DIBs) remains to be established, with the exception of five bands attributed to C60+, although it is generally agreed that DIB carriers should be large carbon-based molecules (with ~10–100 atoms) in the gas phase, such as polycyclic aromatic hydrocarbons (PAHs), long carbon chains or fullerenes. The aim of this paper is to investigate more specific possible carriers among PAHs, namely elongated molecules, which could explain a correlation between the DIB wavelength and the apparent UV resilience of their carriers. More specifically, we address the case of polyacenes, C4N+2H2N+4, with N ~ 10–18 fused rectilinear aligned hexagons. Polyacenes are attractive DIB carrier candidates because their high symmetry and large linear size allow them to form regular series of bands in the visible range with strengths larger than most other PAHs, as confirmed by recent laboratory results up to undecacene (C46H26). Those with very strong bands in the DIB spectral domain are just at the limit of stability against UV photodissociation. They are part of the prominent PAH family of interstellar carbon compounds, meaning that only ~10−5 of the total PAH abundance is enough to account for a medium-strength DIB. After summarizing the limited current knowledge about the complex properties of polyacenes and recent laboratory results, the likelihood that they might meet the criteria for being carriers of some DIBs is addressed by reviewing the following properties: wavelength and strength of their series of visible bands; interstellar stability and abundances, charge state and hydrogenation; and DIB rotation profiles. No definite inconsistency has been identified that precludes polyacenes from being the carriers of some DIBs with medium or weak strength, including the so-called C2 DIBs. But, despite their many interesting properties, additional experimental data about long acenes and their visible bands are needed to make robust conclusions.

scholarly journals Correlation between UV resilience and wavelength of narrow diffuse interstellar bands

2020 ◽  
Vol 637 ◽  
pp. A74
Author(s):  
A. Omont ◽  
H. F. Bettinger
Keyword(s):  
Polycyclic Aromatic Hydrocarbons ◽  
Aromatic Hydrocarbons ◽  
Oscillator Strengths ◽  
Band Width ◽  
Carbon Chains ◽  
Diffuse Interstellar Bands ◽  
Polycyclic Aromatic

Carriers of diffuse interstellar bands (DIBs) still need to be identified. In a recent paper, we reported a correlation between the DIB wavelength and the apparent UV resilience (or boost) of their carriers. We proposed that this might be an indication of the important role of conjugated elongated molecules among the DIB carriers. The aim of this paper is to further understand the origin of this correlation. The analysis of 509 optical DIBs on the lines of sight of HD 183143 and/or HD 204827 reported in the literature shows that this correlation mainly implies the 386 narrow DIBs with a band width <1.1 Å, which include most of the identified DIBs of the C2 and ζ families, while the majority of the 123 broader DIBs, including the identified σ DIBs, do not display such a correlation. We present a possible origin of this correlation from very strong bands of large conjugated elongated molecules, such as carbon chains, polyacenes, or other catacondensed polycyclic aromatic hydrocarbons. The total amount of carbon contained in all the carriers of these narrow DIBs is a very small fraction of the interstellar carbon if their oscillator strengths are ≥1. The amount of carbon locked in the carriers of the broader DIBs is higher, especially if their oscillator strengths are significantly weaker.

Electronic spectroscopy of the nonlinear carbon chains C4H4+ and C8H4+

2004 ◽  
Vol 82 (6) ◽  
pp. 848-853 ◽  
Author(s):  
Mitsunori Araki ◽  
Pawel Cias ◽  
Alexey Denisov ◽  
Jan Fulara ◽  
John P Maier
Keyword(s):  
Gas Phase ◽  
Electronic Transition ◽  
Electronic Spectroscopy ◽  
Carbon Chain ◽  
Cavity Ringdown Spectroscopy ◽  
Cavity Ringdown ◽  
Carbon Chains ◽  
Diffuse Interstellar Bands ◽  
Phase Spectra ◽  
Electronic Transition Energies

The electronic spectrum of a nonlinear carbon chain radical C4H4+ was observed after mass-selective deposition in a 6 K neon matrix. The corresponding gas-phase spectra of C4H4+ and C4D4+ have been observed in the 512 to 513 nm region and at 710 nm for C8H4+. These were detected in direct absorption by cavity ringdown spectroscopy through a supersonic planar discharge. The electronic transition energies of these nonlinear carbon chain radicals correlate well with those of the polyacetylene cations HCnH+ (n = 4, 6, 8). The observed profiles are reproduced with rotational constants obtained by ab initio geometry optimizations and extrapolation between the ground and excited electronic states. Key words: nonlinear carbon chain, carbon cation, electronic transition, diffuse interstellar bands, molecular structure.

scholarly journals Isomer-specific vibronic structure of the 9-, 1-, and 2-anthracenyl radicals via slow photoelectron velocity-map imaging

2016 ◽  
Vol 113 (7) ◽  
pp. 1698-1705 ◽  
Author(s):  
Marissa L. Weichman ◽  
Jessalyn A. DeVine ◽  
Daniel S. Levine ◽  
Jongjin B. Kim ◽  
Daniel M. Neumark
Keyword(s):  
Gas Phase ◽  
Excited States ◽  
Cross Sections ◽  
Electronic Spectroscopy ◽  
Spectroscopic Characterization ◽  
Photoelectron Spectra ◽  
Velocity Map Imaging ◽  
Vibronic Structure ◽  
Quantum Chemistry Calculations ◽  
Franck Condon

Polycyclic aromatic hydrocarbons, in various charge and protonation states, are key compounds relevant to combustion chemistry and astrochemistry. Here, we probe the vibrational and electronic spectroscopy of gas-phase 9-, 1-, and 2-anthracenyl radicals (C14H9) by photodetachment of the corresponding cryogenically cooled anions via slow photoelectron velocity-map imaging (cryo-SEVI). The use of a newly designed velocity-map imaging lens in combination with ion cooling yields photoelectron spectra with <2 cm−1 resolution. Isomer selection of the anions is achieved using gas-phase synthesis techniques, resulting in observation and interpretation of detailed vibronic structure of the ground and lowest excited states for the three anthracenyl radical isomers. The ground-state bands yield electron affinities and vibrational frequencies for several Franck–Condon active modes of the 9-, 1-, and 2-anthracenyl radicals; term energies of the first excited states of these species are also measured. Spectra are interpreted through comparison with ab initio quantum chemistry calculations, Franck–Condon simulations, and calculations of threshold photodetachment cross sections and anisotropies. Experimental measures of the subtle differences in energetics and relative stabilities of these radical isomers are of interest from the perspective of fundamental physical organic chemistry and aid in understanding their behavior and reactivity in interstellar and combustion environments. Additionally, spectroscopic characterization of these species in the laboratory is essential for their potential identification in astrochemical data.

Electronic spectroscopy of PAHs and PAH derivatives in supersonic jet

2019 ◽  
Vol 15 (S350) ◽  
pp. 427-428
Author(s):  
Salma Bejaoui ◽  
Farid Salama
Keyword(s):  
High Resolution ◽  
Polycyclic Aromatic Hydrocarbon ◽  
Aromatic Hydrocarbon ◽  
Gas Phase ◽  
Environmental Conditions ◽  
Spectroscopic Data ◽  
Electronic Spectroscopy ◽  
Supersonic Jet ◽  
Polycyclic Aromatic ◽  
Ubiquitous Presence

AbstractPolycyclic Aromatic Hydrocarbon (PAHs) molecules are attracting much attention in the astrophysical and astrochemical communities because of their ubiquitous presence in space due to their ability to survive in the harsh environmental conditions of the interstellar medium (ISM). The objective of this work is to provide gas phase, high-resolution spectroscopic data on the electronic and vibronic transitions of PAHs and their nitrogenated derivatives measured in astrophysically relevant conditions.

scholarly journals Dissociative Attachment Studies of Halogen-containing Molecules: Problems, Applications and Challenges

1996 ◽  
Vol 49 (2) ◽  
pp. 403 ◽  
Author(s):  
PD Burrow ◽  
GA Gallup ◽  
II Fabrikant ◽  
KD Jordan
Keyword(s):  
Electron Transfer ◽  
Gas Phase ◽  
Cross Sections ◽  
Halogen Atom ◽  
Intramolecular Electron Transfer ◽  
Dissociative Attachment ◽  
Molecular Physics ◽  
The Cross ◽  
Atomic And Molecular Physics

The dissociative attachment (DA) process appears in a surprisingly diverse number of research disciplines. Although gas phase studies have been carried out for approximately 30 years, there are no calculations of the cross sections for this process in molecules larger than diatomics. In this presentation, we review briefly the role of DA in several contexts generally unfamiliar to workers in atomic and molecular physics, and touch on some of the theoretical difficulties. We continue with a discussion of our work, both experimental and theoretical, on compounds containing a single halogen atom and conclude with results showing how the DA process can be used to study intramolecular electron transfer.

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