HIGH-RESOLUTION IR ABSORPTION SPECTROSCOPY OF POLYCYCLIC AROMATIC HYDROCARBONS IN THE 3 μm REGION: ROLE OF PERIPHERY

Maltseva, Elena; Petrignani, Annemieke; Candian, Alessandra; Mackie, Cameron J.; Huang, Xinchuan; Lee, Timothy J.; Tielens, A. G. G. M.; Buma, Wybren Jan

doi:10.3847/0004-637x/831/1/58

Cited by 51 publications

(66 citation statements)

References 44 publications

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“…40 Therefore, we estimate this factor using B3LYP/6-311+G(d,p) computed spectra for pyrene and phenanthrene and comparing the CH-stretch frequencies with accurate gas-phase IR data. 42 A scale factor of 0.9610±0.0005 is established, in agreement with Ref. 40.…”

Section: Experiments Were Performed In a Modified 3-d Quadrupole Ion supporting

confidence: 86%

The infrared spectrum of protonated buckminsterfullerene C60H+

2019

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Although fullerenes have long been hypothesized to occur in interstellar environments, their actual unambiguous spectroscopic identification is of more recent date. 1-4 C 60 , C 70 and C + 60 now constitute the largest molecular species individually identified in the interstellar medium (ISM). Fullerenes have significant proton affinities and it was suggested that C 60 H + is likely the most abundant interstellar analogue of C 60 . 5 We present here the first laboratory infrared (IR) spectrum of gaseous C 60 H + . Symmetry breaking relative to C 60 produces an IR spectrum that is much richer than that of C 60 . The experimental spectrum is used to benchmark theoretical spectra indicating that the B3LYP density functional with the 6-311+G(d,p) basis set accurately reproduces the spectrum. Comparison with IR emission spectra from two planetary nebulae, SMP LMC56 and SMC16, that have been associated with high C 60 abundances, indicate that C 60 H + is a plausible contributor to their IR emission.Buckminsterfullerene C 60 is undoubtedly one of the most iconic molecules of our time. Since its discovery in 1985, 6 its physico-chemical properties have been extensively characterized, including its ion chemistry and spectroscopic properties. IR spectra have been reported in condensed and gas phases, 7-10 and spectra for ionized forms are available as well. 4,8,11,12 The high cosmic abundance of carbon combined with the high stability of fullerenes 13 initiated a quest for their detection in inter-and circumstellar environments. [14][15][16][17] This search culminated in the identifications of neutral C 60 and C 70 in a young planetary nebula (Tc1) 1 based on diagnostic IR features. Accurate gas-phase laboratory spectra in the near-IR range led to the identification of C + 60 as carrier of two of the diffuse interstellar bands near 9600Å. 4 The question of whether or not fullerenes can form in H-rich regions of the interstellar medium (ISM) has been under debate. 1,3 Hydrogenation produces stable fullerene derivatives and partially hydrogenated fullerenes (fulleranes) have been suggested to occur in circumstellar envelopes and in the ISM 3,18,19 . On the other hand, hydrogenation and the concomitant change in orbital hybridization from sp 2 to sp 3 reduces the stability of the fullerene cage, which under the conditions of the ISM would likely lead to dehydrogenation and restoration of the original fullerene 20 or to breakdown of the carbon cage. 5 However, in this latter paper, Kroto also noted that protonation does not compromise cage stability and hypothesized that "protonated C 60 is likely to be the most abundant fullerene analogue," analogous to high abundances of protonated carbon monoxide, HCO + .Ion chemistry studies 21 have determined the proton affinity (PA) of C 60 at 860 kJ/mol. This relatively high value, just above the PA of ammonia, makes C 60 H + (Figure 1a) one of the most relevant stable fullerene derivatives and underpins Kroto's statement above. However, a) Corresponding author: j.oomens@science.ru.nl t...

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Section: Experiments Were Performed In a Modified 3-d Quadrupole Ion supporting

confidence: 86%

The infrared spectrum of protonated buckminsterfullerene C60H+

2019

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“…25 for a comparison in the C-H stretching region) the anharmonic calculations provide a vast improvement. Harmonic frequencies are off by typically over 4%, whereas the anharmonic frequencies are off by less than 1%.…”

Section: Discussionmentioning

confidence: 99%

“…A dye laser (Sirah Cobra Stretch) was fixed on a specific electronic transition of the molecule under investigation (see Ref. 25 for more details) while an ArF excimer laser beam (Neweks PSX-501) in temporal overlap with the dye laser was used to ionize the molecules from the electronically excited state.…”

Section: Experimental Methods (High-resolution Gas-phase)mentioning

confidence: 99%

“…1). Moreover, we present low-temperature high-resolution gasphase experimental IR absorption spectra of the five non-linear PAHs (first presented in the astrophysical companion paper 25 ), as well as matrix-isolation spectra (MIS) which allows for direct comparisons with theory providing further validation for our approach. Although the theoretical spectra produced are in absorption at 0 K, understanding the fundamental nature of the anharmonicity of PAHs and the importance of resonances will allow us to better understand the emission features of astronomical PAHs.…”

Section: 19mentioning

confidence: 99%

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The anharmonic quartic force field infrared spectra of five non-linear polycyclic aromatic hydrocarbons: Benz[a]anthracene, chrysene, phenanthrene, pyrene, and triphenylene

Mackie

Candian

Huang

et al. 2016

The Journal of Chemical Physics

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The anharmonic quartic force field infrared spectra of three polycyclic aromatic hydrocarbons: Naphthalene, anthracene, and tetracene J. Chem. Phys. 143, 224314224314 (2015); 10.1063/1.4936779 THE JOURNAL OF CHEMICAL PHYSICS 145, 084313 (2016) The anharmonic quartic force field infrared spectra of five non The study of interstellar polycyclic aromatic hydrocarbons (PAHs) relies heavily on theoretically predicted infrared spectra. Most earlier studies use scaled harmonic frequencies for band positions and the double harmonic approximation for intensities. However, recent high-resolution gas-phase experimental spectroscopic studies have shown that the harmonic approximation is not sufficient to reproduce experimental results. In our previous work, we presented the anharmonic theoretical spectra of three linear PAHs, showing the importance of including anharmonicities into the theoretical calculations. In this paper, we continue this work by extending the study to include five non-linear PAHs (benz[a]anthracene, chrysene, phenanthrene, pyrene, and triphenylene), thereby allowing us to make a full assessment of how edge structure, symmetry, and size influence the effects of anharmonicities. The theoretical anharmonic spectra are compared to spectra obtained under matrix isolation low-temperature conditions, low-resolution, high-temperature gas-phase conditions, and high-resolution, low-temperature gas-phase conditions. Overall, excellent agreement is observed between the theoretical and experimental spectra although the experimental spectra show subtle but significant differences. Published by AIP Publishing.[http://dx

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“…4, in the center the 3.4 µm feature is much weaker than the 3.3 µm feature, in contrast, in the superwind the 3.4 µm feature supercedes the 3.3 µm feature and dominates the near-IR spectra. While the 3.3 µm emission arises from the aromatic C-H stretch, the 3.4 µm complex is commonly attributed to the aliphatic side chains attached as functional groups to the aromatic skeleton of PAHs [32][33][34] , although superhydrogenated PAHs (i.e., PAHs whose edges contain excess H atoms) of which the extra H atom converts the originally aromatic ring into an aliphatic ring [90][91][92][93][94] , and the anharmonicity of the aromatic C-H stretch 95,96 could also be responsible for the 3.4 µm feature. The intensity ratio of the 3.4 µm aliphatic band to the 3.3 µm aromatic band is often used to derive the aliphatic fraction (i.e., the fraction of carbon atoms in aliphatic form) of PAHs [97][98][99] .…”

Section: The Spitzer Legacy Of Pah Astrophysicsmentioning

confidence: 99%

Spitzer’s perspective of polycyclic aromatic hydrocarbons in galaxies

2020

Nat Astron

160

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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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HIGH-RESOLUTION IR ABSORPTION SPECTROSCOPY OF POLYCYCLIC AROMATIC HYDROCARBONS IN THE 3 μm REGION: ROLE OF PERIPHERY

Cited by 51 publications

References 44 publications

The infrared spectrum of protonated buckminsterfullerene C60H+

The infrared spectrum of protonated buckminsterfullerene C60H+

The anharmonic quartic force field infrared spectra of five non-linear polycyclic aromatic hydrocarbons: Benz[a]anthracene, chrysene, phenanthrene, pyrene, and triphenylene

Spitzer’s perspective of polycyclic aromatic hydrocarbons in galaxies

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