Deuterated polycyclic aromatic hydrocarbons: Revisited

Doney, Kirstin D.; Candian, Alessandra; Mori, Tamami; Onaka, Takashi; Tielens, A. G. G. M.

doi:10.1051/0004-6361/201526809

Cited by 31 publications

(64 citation statements)

References 49 publications

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“…PAHs of intermediate size (with < ∼ 100 C atoms) are expected to become deuterium enriched in the ISM through the selective loss of hydrogen during photodissociation events 168 . While ISO/SWS and AKARI observations have reported the tentative detection of the C-D bands at 4.4 and 4.65 µm in the Orion Bar and M17 PDRs 169,170 and HII regions 171 , the unique high sensitivity of JWST/NIRSpec will place the detection of deuterated PAHs on firm ground and enable far more detailed band analysis than previously possible.…”

Section: Discussionmentioning

confidence: 96%

Spitzer’s perspective of polycyclic aromatic hydrocarbons in galaxies

2020

Nat Astron

161

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Polycyclic aromatic hydrocarbon (PAH) molecules, as revealed by the distinctive set of emission bands at 3. 3, 6.2, 7.7, 8.6, 11.3 and 12.7 µm characteristic of their vibrational modes, are abundant and widespread throughout the Universe. They are ubiquitously seen in a wide variety of astrophysical regions, ranging from planet-forming disks around young stars to the interstellar medium (ISM) of the Milky Way and external galaxies out to high redshifts at z > ∼ 4. PAHs profoundly influence the thermal budget and chemistry of the ISM by dominating the photoelectric heating of the gas and controlling the ionization balance. Here, we review the current state of knowledge of the astrophysics of PAHs, focusing on their observational characteristics obtained from the Spitzer Space Telescope and their diagnostic power for probing the local physical and chemical conditions and processes. Special attention is paid to the spectral properties of PAHs and their variations revealed by the Infrared Spectrograph (IRS) on board Spitzer across a much broader range of extragalactic environments (e.g., distant galaxies, early-type galaxies, galactic halos, active galactic nuclei, and low-metallicity galaxies) than was previously possible with the Infrared Space Observatory (ISO) or any other telescope facilities. Also highlighted is the relation between the PAH abundance and the galaxy metallicity established for the first time by Spitzer.

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Section: Discussionmentioning

confidence: 96%

Spitzer’s perspective of polycyclic aromatic hydrocarbons in galaxies

2020

Nat Astron

161

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“…; Doney et al. ). Our hypothesis may help to explain how D enrichments are retained as the formation of a hydrophobic melt directly from a solid would limit D/H isotopic exchange between the OM and aqueous solution.…”

Section: Discussionmentioning

confidence: 99%

The evolution of polycyclic aromatic hydrocarbons under simulated inner asteroid conditions

Giese

Kate

Plümper

et al. 2019

Meteorit & Planetary Scien

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Large polycyclic aromatic hydrocarbons (PAHs) are an important component of the interstellar medium. PAHs have been identified in the soluble and insoluble matter of carbonaceous chondrites (CCs). Here, we study the evolution of PAHs under conditions relevant to the interiors of asteroids and compare our results to PAHs observed in CCs. We have performed long‐term and short‐term hydrothermal experiments, in which we exposed PAH‐mineral mixture analogs of meteorites to temperature conditions representative of those predicted for asteroids interiors. Our results show that small PAHs with melting points within the aqueous alteration temperature of CCs form carbonaceous spherules in the presence of water. In this work, we describe the microstructure and morphology of these spherules. We discuss the similarities and differences compared to globules isolated from CCs.

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“…where (I 3.3 /I 4.4 ) obs is the observed ratio of the power emitted from the 3.3 µm aromatic C-H band (I 3.3 ) to that from the 4.4 µm aromatic C-D band (I 4.4 ), B 3.3 and B 4.4 are respectively the Planck functions at temperature T and wavelengths 3.3 µm and 4.4 µm, and A 3.3 and A 4.4 are respectively the intrinsic band strengths of the aromatic C-H and C-D stretches (on a per C-H or C-D bond basis). Yang et al (2020b) have compiled all the available observational data on (I 3.3 /I 4.4 ) obs (Peeters et al 2004, Onaka et al 2014, Doney et al 2016 and obtained a mean value of (I 3.3 /I 4.4 ) obs ≈ 52.6. With B 3.3 /B 4.4 ≈ 0.70 ± 0.28 (suitable for 400 T 900 K) and A 4.4 /A 3.3 ≈ 0.56 for both mono-deuterated species (Yang et al 2020b) and multi-deuterated species (this work), we estimate [D/H] PAH ≈ 2.4%.…”

Section: Discussion and Astrophysical Implicationsmentioning

confidence: 99%

Deuterated Polycyclic Aromatic Hydrocarbons in the Interstellar Medium: The C–D Band Strengths of Monodeuterated Species

Yang

et al. 2020

ApJS

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Observationally, the interstellar gas-phase abundance of deuterium (D) is considerably depleted and the missing D atoms are often postulated to have been locked up into carbonaceous solids and polycyclic aromatic hydrocarbon (PAH) molecules. An accurate knowledge of the fractional amount of D (relative to H) tied up in carbon dust and PAHs has important cosmological implications since D originated exclusively from the Big Bang and the present-day D abundance, after accounting for the astration it has experienced during the Galactic evolution, provides essential clues to the primordial nucleosynthesis and the cosmological parameters. To quantitatively explore the extent to which PAHs could possibly accommodate the observed D depletion, we have previously quantum-chemically computed the infrared vibrational spectra of mono-deuterated PAHs and derived the mean intrinsic band strengths of the 3.3 µm C-H stretch (A 3.3 ) and the 4.4 µm C-D stretch (A 4.4 ). Here we extend our previous work to multi-deuterated PAH species of different deuterations, sizes and structures. We find that both the intrinsic band strengths A 3.3 and A 4.4 and their ratios A 4.4 /A 3.3 not only show little variations among PAHs of different deuterations, sizes and structures, they are also closely similar to that of mono-deuterated PAHs. Therefore, a PAH deuteration level (i.e., the fraction of peripheral atoms attached to C atoms in the form of D) of ∼ 2.4% previously estimated from the observed 4.4 µm to 3.3 µm band ratio based on the A 4.4 /A 3.3 ratio of mono-deuterated PAHs is robust.

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Deuterated polycyclic aromatic hydrocarbons: Revisited

Cited by 31 publications

References 49 publications

Spitzer’s perspective of polycyclic aromatic hydrocarbons in galaxies

Spitzer’s perspective of polycyclic aromatic hydrocarbons in galaxies

The evolution of polycyclic aromatic hydrocarbons under simulated inner asteroid conditions

Deuterated Polycyclic Aromatic Hydrocarbons in the Interstellar Medium: The C–D Band Strengths of Monodeuterated Species

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