Detection of two interstellar polycyclic aromatic hydrocarbons via spectral matched filtering

McGuire, Brett A.; Loomis, Ryan A.; Burkhardt, Andrew M.; Lee, Kelvin; Shingledecker, Christopher N.; Charnley, Steven B.; Cooke, Ilsa R.; Cordiner, Martin; Herbst, Eric; Kalenskii, S. V.; Siebert, Mark A.; Willis, Eric R.; Xue, Ci; Remijan, Anthony J.; McCarthy, Michael

doi:10.1126/science.abb7535

Cited by 298 publications

(322 citation statements)

References 54 publications

(21 reference statements)

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“…These approaches are rooted into the hypothesis that the largest source of errors in VPT2 results is related to the harmonic reference data, so that a good accuracy can be obtained by combining harmonic results produced by a very accurate electronic structure method, (e.g., CCSD(T)) with anharmonic contributions evaluated at a lower level, (e.g., DFT employing hybrid functionals) (Puzzarini et al, 2010;Barone et al, 2013aBarone et al, , 2015Puzzarini et al, 2019). Of course, even harmonic contributions need to be computed by relatively cheap quantum mechanical methods, (e.g., DFT) for very large molecules, like polycyclic aromatic hydrocarbons or biomolecules (McGuire et al, 2021).…”

Section: Introductionmentioning

confidence: 99%

Accuracy and Reliability in the Simulation of Vibrational Spectra: A Comprehensive Benchmark of Energies and Intensities Issuing From Generalized Vibrational Perturbation Theory to Second Order (GVPT2)

Yang

Mendolicchio

Barone

et al. 2021

Front. Astron. Space Sci.

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Vibrational spectroscopy represents an active frontier for the identification and characterization of molecular species in the context of astrochemistry and astrobiology. As new missions will provide more data over broader ranges and at higher resolution, especially in the infrared region, which could be complemented with new spectrometers in the future, support from laboratory experiments and theory is crucial. In particular, computational spectroscopy is playing an increasing role in deepening our understanding of the origin and nature of the observed bands in extreme conditions characterizing the interstellar medium or some planetary atmospheres, not easily reproducible on Earth. In this connection, the best compromise between reliability, feasibility and ease of interpretation is still a matter of concern due to the interplay of several factors in determining the final spectral outcome, with larger molecular systems and non-covalent complexes further exacerbating the dichotomy between accuracy and computational cost. In this context, second-order vibrational perturbation theory (VPT2) together with density functional theory (DFT) has become particularly appealing. The well-known problem of the reliability of exchange-correlation functionals, coupled with the treatment of resonances in VPT2, represents a challenge for the determination of standardized or “black-box” protocols, despite successful examples in the literature. With the aim of getting a clear picture of the achievable accuracy and reliability of DFT-based VPT2 calculations, a multi-step study will be carried out here. Beyond the definition of the functional, the impact of the basis set and the influence of the resonance treatment in VPT2 will be analyzed. For a better understanding of the computational aspects and the results, a short summary of vibrational perturbation theory and the overall treatment of resonances for both energies and intensities will be given. The first part of the benchmark will focus on small molecules, for which very accurate experimental and theoretical data are available, to investigate electronic structure calculation methods. Beyond the reliability of energies, widely used for such systems, the issue of intensities will also be investigated in detail. The best performing electronic structure methods will then be used to treat larger molecular systems, with more complex topologies and resonance patterns.

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Section: Introductionmentioning

confidence: 99%

Accuracy and Reliability in the Simulation of Vibrational Spectra: A Comprehensive Benchmark of Energies and Intensities Issuing From Generalized Vibrational Perturbation Theory to Second Order (GVPT2)

Yang

Mendolicchio

Barone

et al. 2021

Front. Astron. Space Sci.

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“…Benzonitrile, and more recently the naphthalene equivalents 1cyanonaphthalene and 2-cyanonaphthalene, have been detected in the cold, dark molecular cloud TMC-1 (McGuire et al 2018(McGuire et al , 2021. We searched for a The spectra were acquired at a native resolution of 1.4 kHz, corresponding to a velocity resolution of 0.01-0.05 km s −1 across the full bandwidth of the observations.…”

Section: Observationsmentioning

confidence: 99%

Hunting the relatives of benzonitrile: Rotational spectroscopy of dicyanobenzenes

Chitarra

Lee

Buchanan

et al. 2021

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Context. The recent interstellar detections of -CN containing aromatic species, namely benzonitrile, 1-cyanonaphthalene, and 2cyanonaphthalene, bring renewed interest in related molecules that could participate in similar reaction networks. Aims. To enable new interstellar searches for benzonitrile derivatives, the pure rotational spectra of several related species need to be investigated in the laboratory. Methods. We have recorded the pure rotational spectra of ortho-and meta-dicyanobenzene in the centimetre and millimetre-wave domains. Assignments were supported by high-level quantum chemical calculations. Using Markov chain Monte Carlo simulations, we also searched for evidence of these molecules towards TMC-1 using the GOTHAM survey. Results. Accurate spectroscopic parameters are derived from the analysis of the experimental spectra, allowing for reliable predictions at temperatures of interest (i.e. 10-300 K) for astronomical searches. Our searches in TMC-1 for both ortho-and meta-isomers provide upper limits for the abundances of the species.

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“…Their presence in the ISM is inferred from the strong IR emission in the aromatic bands corresponding to the various CH or C-C vibration modes. However, no individual interstellar PAH is identified yet except for CN-naphthalene, which was detected very recently in a dense cloud well shielded from UV radiation (McGuire et al (2021)). Altogether, PAHs typically contain ∼10% of all interstellar carbon, which makes them one of the main reservoirs of interstellar carbon together with C + , CO, and carbon dust.…”

Section: Introductionmentioning

confidence: 99%

Intermediate-size fullerenes as degradation products of interstellar polycyclic aromatic hydrocarbons

Omont

Bettinger

2021

A&A

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The high interstellar abundances of polycyclic aromatic hydrocarbons (PAHs) and their size distribution are the result of complex chemical processes implying dust, UV radiation, and the main gaseous components (H, C+, and O). These processes must explain the high abundance of relatively small PAHs in the diffuse interstellar medium (ISM) and imply the continuous formation of some PAHs that are small enough (number of carbon atoms NC < ~35–50) to be completely dehydrogenated by interstellar UV radiation. The carbon clusters Cn thus formed are constantly exposed to the absorption of ~10–13.6 eV UV photons, allowing isomerization and favoring the formation of the most stable isomers. They might tend to form irregular carbon cages. The frequent accretion of interstellar C+ ions could favor further cage isomerization, as is known in the laboratory for C60, possibly yielding most stable fullerenes, such as C40, C44, and C50. These fullerenes are expected to be very stable in the diffuse ISM because C2 ejection is not possible by single UV photon absorption, but could need rare two-photon absorption. It is possible that at least one of these fullerenes or its cation is as abundant as C60 or C60+ in the diffuse ISM, although this abundance is limited by the lack of observed matching features in observed mid-infrared spectra. B3LYP calculations of the visible spectrum for a number of fullerene isomers with 40 ≤NC ≤ 50 show that they generally have a few spectral bands in the visible range, with f-values in the range of a few 10−2. This could make such fullerenes interesting candidates for the carriers of some diffuse interstellar bands.

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Detection of two interstellar polycyclic aromatic hydrocarbons via spectral matched filtering

Cited by 298 publications

References 54 publications

Accuracy and Reliability in the Simulation of Vibrational Spectra: A Comprehensive Benchmark of Energies and Intensities Issuing From Generalized Vibrational Perturbation Theory to Second Order (GVPT2)

Accuracy and Reliability in the Simulation of Vibrational Spectra: A Comprehensive Benchmark of Energies and Intensities Issuing From Generalized Vibrational Perturbation Theory to Second Order (GVPT2)

Hunting the relatives of benzonitrile: Rotational spectroscopy of dicyanobenzenes

Intermediate-size fullerenes as degradation products of interstellar polycyclic aromatic hydrocarbons

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