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Esposito VJ, Fortenberry RC, Boersma C, Allamandola LJ. Assigning the CH stretch overtone spectrum of benzene and naphthalene with extension to anthracene and tetracene using 2- and 3-quanta anharmonic quantum chemical computations. J Chem Phys 2024; 160:211101. [PMID: 38828805 DOI: 10.1063/5.0208597] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2024] [Accepted: 05/05/2024] [Indexed: 06/05/2024] Open
Abstract
The CH stretch overtone region (5750-6300 cm-1) of benzene and naphthalene is assigned herein using anharmonic quantum chemical computations, and the trend of how this extends to larger polycyclic aromatic hydrocarbons (PAHs) is established. The assignment of all experimental bands to specific vibrational states is performed for the first time. Resonance polyads and the inclusion of 3-quanta vibrational states are both needed to compute accurate vibrational frequencies with the proper density-of-states to match the experimental band shape. Hundreds of 3-quanta states produce the observed band structure in naphthalene, anthracene, and tetracene, and this number is expected to increase drastically for larger PAHs. The width and shape of the main peak are consistent from naphthalene to anthracene, necessitating further exploration of this trend to confirm whether it is representative of all PAHs in the CH stretch overtone region. Understanding observations of PAH sources in the 1-3 μm region from the NIRSpec instrument aboard JWST requires new computational data, and this study provides a benchmark and foundation for their computation.
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Affiliation(s)
- Vincent J Esposito
- Astrophysics Branch, NASA Ames Research Center, Moffett Field, California 94035, USA
| | - Ryan C Fortenberry
- Department of Chemistry and Biochemistry, University of Mississippi, University, Mississippi 38677-1848, USA
| | - Christiaan Boersma
- Astrophysics Branch, NASA Ames Research Center, Moffett Field, California 94035, USA
| | - Louis J Allamandola
- Astrophysics Branch, NASA Ames Research Center, Moffett Field, California 94035, USA
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2
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Esposito VJ, Ferrari P, Buma WJ, Fortenberry RC, Boersma C, Candian A, Tielens AGGM. The infrared absorption spectrum of phenylacetylene and its deuterated isotopologue in the mid- to far-IR. J Chem Phys 2024; 160:114312. [PMID: 38501470 DOI: 10.1063/5.0191404] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2023] [Accepted: 02/18/2024] [Indexed: 03/20/2024] Open
Abstract
Anharmonicity strongly influences the absorption and emission spectra of polycyclic aromatic hydrocarbon (PAH) molecules. Here, IR-UV ion-dip spectroscopy experiments together with detailed anharmonic computations reveal the presence of fundamental, overtone, as well as 2- and 3-quanta combination band transitions in the far- and mid-infrared absorption spectra of phenylacetylene and its singly deuterated isotopologue. Strong absorption features in the 400-900 cm-1 range originate from CH(D) in-plane and out-of-plane wags and bends, as well as bending motions including the C≡C and CH bonds of the acetylene substituent and the aromatic ring. For phenylacetylene, every absorption feature is assigned either directly or indirectly to a single or multiple vibrational mode(s). The measured spectrum is dense, broad, and structureless in many regions but well characterized by computations. Upon deuteration, large isotopic shifts are observed. At frequencies above 1500 cm-1 for d1-phenylacetylene, a one-to-one match is seen when comparing computations and experiments with all features assigned to combination bands and overtones. The C≡C stretch observed in phenylacetylene is not observed in d1-phenylacetylene due to a computed 40-fold drop in intensity. Overall, a careful treatment of anharmonicity that includes 2- and 3-quanta modes is found to be crucial to understand the rich details of the infrared spectrum of phenylacetylene. Based on these results, it can be expected that such an all-inclusive anharmonic treatment will also be key for unraveling the infrared spectra of PAHs in general.
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Affiliation(s)
- Vincent J Esposito
- NASA Ames Research Center, MS 245-6, Moffett Field, California 94035, USA
| | - Piero Ferrari
- Radboud University, Institute for Molecules and Materials, HFML-FELIX, 6525 ED Nijmegen, The Netherlands
| | - Wybren Jan Buma
- Radboud University, Institute for Molecules and Materials, HFML-FELIX, 6525 ED Nijmegen, The Netherlands
- Van't Hoff Institute for Molecular Sciences, University of Amsterdam, 1098 XH Amsterdam, The Netherlands
| | - Ryan C Fortenberry
- Department of Chemistry and Biochemistry, University of Mississippi, University, Mississippi 38677-1848, USA
| | - Christiaan Boersma
- NASA Ames Research Center, MS 245-6, Moffett Field, California 94035, USA
| | - Alessandra Candian
- Anton Pannekoek Institute for Astronomy, University of Amsterdam, 1098 XH Amsterdam, The Netherlands
| | - Alexander G G M Tielens
- Leiden Observatory, Leiden University, 2333 CA Leiden, The Netherlands
- Astronomy Department, University of Maryland, College Park, Maryland 20742-2421, USA
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3
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Fortenberry RC. Quantum Chemistry and Astrochemistry: A Match Made in the Heavens. J Phys Chem A 2024; 128:1555-1565. [PMID: 38381079 DOI: 10.1021/acs.jpca.3c07601] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/22/2024]
Abstract
Quantum chemistry can uniquely answer astrochemical questions that no other technique can provide. Computations can be parallelized, automated, and left to run continuously providing exceptional molecular throughput that cannot be done through experimentation. Additionally, the granularity of the individual computations that are required of potential energy surfaces, reaction mechanism pathways, or other quantum chemically derived observables produces a unique mosaic that make up the larger whole. These pieces can be dissected for their individual contributions or evaluated in an ad hoc fashion for each of their roles in generating the larger whole. No other scientific approach is capable of reporting such fine-grained insights. Quantum chemistry also works from a bottom-up approach in providing properties directly from the desired molecule instead of a top-down perspective as required of experiment where molecules have to be linked to observed phenomena. Furthermore, modern quantum chemistry is well within the range of "chemical accuracy" and is approaching "spectroscopic accuracy." As such, the seemingly difficult questions asked by astrochemistry that would not be asked initially for any other application require quantum chemical reference data. While the results of quantum chemical computations are needed to interpret astrochemical observation, modeling, or laboratory experimentation, such hard questions, regardless of the original need to answer them, produce unique solutions. While questions in astrochemistry often require novel developments in and implementations of quantum chemistry as outlined herein, the applications of these solutions will stretch beyond astrochemistry and may yet impact fields much closer to Earth.
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Affiliation(s)
- Ryan C Fortenberry
- Department of Chemistry & Biochemistry, University of Mississippi, Oxford, Mississippi 38677-1848, United States
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4
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Lemmens AK, Mackie CJ, Candian A, Lee TMJ, Tielens AGGM, Rijs AM, Buma WJ. Size distribution of polycyclic aromatic hydrocarbons in space: an old new light on the 11.2/3.3 μm intensity ratio. Faraday Discuss 2023; 245:380-390. [PMID: 37294543 PMCID: PMC10510036 DOI: 10.1039/d2fd00180b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2022] [Accepted: 02/02/2023] [Indexed: 09/21/2023]
Abstract
The intensity ratio of the 11.2/3.3 μm emission bands is considered to be a reliable tracer of the size distribution of polycyclic aromatic hydrocarbons (PAHs) in the interstellar medium (ISM). This paper describes the validation of the calculated intrinsic infrared (IR) spectra of PAHs that underlie the interpretation of the observed ratio. The comparison of harmonic calculations from the NASA Ames PAH IR spectroscopic database to gas-phase experimental absorption IR spectra reveals a consistent underestimation of the 11.2/3.3 μm intensity ratio by 34%. IR spectra based on higher level anharmonic calculations, on the other hand, are in very good agreement with the experiments. While there are indications that the 11.2/3.3 μm ratio increases systematically for PAHs in the relevant size range when using a larger basis set, it is unfortunately not yet possible to reliably calculate anharmonic spectra for large PAHs. Based on these considerations, we have adjusted the intrinsic ratio of these modes and incorporated this in an interstellar PAH emission model. This corrected model implies that typical PAH sizes in reflection nebulae such as NGC 7023 - previously inferred to be in the range of 50 to 70 carbon atoms per PAH are actually in the range of 40 to 55 carbon atoms. The higher limit of this range is close to the size of the C60 fullerene (also detected in reflection nebulae), which would be in line with the hypothesis that, under appropriate conditions, large PAHs are converted into the more stable fullerenes in the ISM.
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Affiliation(s)
- Alexander K Lemmens
- Van 't Hoff Institute for Molecular Sciences, University of Amsterdam, 1098 XH Amsterdam, The Netherlands.
- Radboud University, Institute for Molecules and Materials, FELIX Laboratory, 6525 ED Nijmegen, The Netherlands
| | - Cameron J Mackie
- Kenneth S. Pitzer Center for Theoretical Chemistry, Department of Chemistry, University of California, Berkeley, California 94720, USA
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
| | - Alessandra Candian
- Van 't Hoff Institute for Molecular Sciences, University of Amsterdam, 1098 XH Amsterdam, The Netherlands.
- Anton Pannekoek Institute for Astronomy, University of Amsterdam, 1098 XH Amsterdam, The Netherlands
| | - Timothy M J Lee
- NASA Ames Research Center, Moffett Field, California 94035-1000, USA
| | | | - Anouk M Rijs
- Division of BioAnalytical Chemistry, AIMMS Amsterdam Institute of Molecular and Life Sciences, Faculty of Science, Vrije Universiteit Amsterdam, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands
| | - Wybren Jan Buma
- Van 't Hoff Institute for Molecular Sciences, University of Amsterdam, 1098 XH Amsterdam, The Netherlands.
- Radboud University, Institute for Molecules and Materials, FELIX Laboratory, 6525 ED Nijmegen, The Netherlands
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5
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Villani L, Mohire NR, Robertson EG. When Phenyl and Cyclopropyl Rings Meet: Spectroscopic Shifts and Conformational Questions. J Phys Chem A 2023; 127:7557-7567. [PMID: 37650854 DOI: 10.1021/acs.jpca.3c04314] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/01/2023]
Abstract
The electronic and vibrational spectra of cyclopropylbenzene (CPB) and 1,3-bromocyclopropylbenzene (BrCPB) in the gas phase were investigated using quantum chemical calculations in combination with resonance-enhanced multi-photon ionization REMPI techniques including 1c-R2PI, UV-UV holeburning, and IR-UV ion depletion in the CH stretch region. The electronic spectra revealed the presence of a single conformer for both species, with the absence of any perpendicular conformer attributed to low computed barriers to conformer interconversion. Assignment of CPB to the bisected conformer was made through interpreting distinctive CH stretch bands in the IR-UV spectrum in conjunction with quantum chemical calculations. A local anharmonic model based on DFT calculations was adapted to reproduce the cyclopropyl CH stretch spectrum successfully. It was not feasible to definitively assign which bisected conformer of BrCPB was observed using vibrational information alone due to the close similarity of their predicted IR spectra. However, conformational sensitivity of the S1 ← S0 transition dipole moment (TDM) alignments leads to simulated rotational contours that display stark differences, which prompted assignment to the "B1" bisecting conformer with the cyclopropyl ring directed away from the bromine atom. The absence of the energetically comparable "B2" conformer is unexpected. The analysis of the convolution of aromatic and aliphatic modes serves as a basis for assignment in constrained aliphatic systems.
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Affiliation(s)
- Luigi Villani
- Department of Biochemistry and Chemistry, La Trobe Institute for Molecular Science, La Trobe University, Melbourne, Victoria 3086, Australia
| | - Nishit R Mohire
- Department of Biochemistry and Chemistry, La Trobe Institute for Molecular Science, La Trobe University, Melbourne, Victoria 3086, Australia
| | - Evan G Robertson
- Department of Biochemistry and Chemistry, La Trobe Institute for Molecular Science, La Trobe University, Melbourne, Victoria 3086, Australia
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6
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Sharma D, Roy TK. Accuracy of Different Electronic Basis Set Families for Anharmonic Molecular Vibrations: A Comprehensive Benchmark Study. J Phys Chem A 2023; 127:7132-7147. [PMID: 37603414 DOI: 10.1021/acs.jpca.3c02874] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/23/2023]
Abstract
In this work, the accuracy and convergence of different electronic basis set families for the computation of anharmonic molecular vibrational spectroscopic calculations are benchmarked. A series of 39 different basis sets from different families following their hierarchy are assessed on VSCF and VSCF-PT2 algorithms with commonly used MP2 and DFT based B3LYP-D potentials for a set of molecular systems. Such an effort has been validated in a previous work ( J. Phys. Chem. A 2020, 124, 9203-9221) with split-valence basis sets for fundamentals and intensities. Here, fundamental transitions, vibrationally excited states, and intensities are compared with the experimental data to estimate the accuracy for a series of Jensen, Dunning, Calendar, Karlsruhe, and Sapporo basis set families. The convergence of basis sets are also compared with the large ANO basis set. Comprehensive statistical error analysis in terms of accuracy and precision was carried out to assess the performance of each basis set. It is observed that the improvement for the calculated harmonic and anharmonic values from the smaller basis sets to the medium (i.e., triple-ξ) is considerable. Beyond this, from medium to large basis sets, the convergence is slow and mostly posits nearly converged values. Basis sets with and without diffuse functions offer characteristically different accuracies and convergence patterns. Finally, recommendations are given on the choice of basis set chosen as black-box which can balance between accuracy and computational time, estimation of the errors, and their selections especially for large molecules.
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Affiliation(s)
- Dhiksha Sharma
- Department of Chemistry and Chemical Sciences, Central University of Jammu, Rahya-Suchani (Bagla), Jammu, J&K 181143 India
| | - Tapta Kanchan Roy
- Department of Chemistry and Chemical Sciences, Central University of Jammu, Rahya-Suchani (Bagla), Jammu, J&K 181143 India
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7
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Lacinbala O, Féraud G, Vincent J, Pino T. Aromatic and Acetylenic C-H or C-D Stretching Bands Anharmonicity Detection of Phenylacetylene by UV Laser-Induced Vibrational Emission. J Phys Chem A 2022; 126:4891-4901. [PMID: 35880827 DOI: 10.1021/acs.jpca.2c01436] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The anharmonic infrared (IR) emission spectra of phenylacetylene C6H5CCH and an isotopologue C6H5CCD induced by 193 nm UV excitation have been investigated in the gas phase. The study has been operated with a homemade IR spectrometer enabling to record time- and wavelength-resolved spectra between 2.5 and 4.5 μm, emitted all along the collisional cooling. The analysis is supported by a kinetic Monte Carlo simulation in the vibrational harmonic approximation. For both species, the anharmonic shifts of the acetylenic C-H or C-D stretching modes and the aromatic C-H stretching modes are studied for band positions and bandwidths in terms of the internal energy. For C6H5CCD, the internal energy dependence of the emission intensity band ratio is investigated and rationalized. This work demonstrates the potential of time-resolved IR emission spectroscopy to explore anharmonicity of astrophysically relevant molecules.
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Affiliation(s)
- Ozan Lacinbala
- Institut des Sciences Moléculaires d'Orsay (ISMO), Université Paris-Saclay, CNRS, 91405 Orsay, France
| | - Géraldine Féraud
- CNRS, LERMA, Sorbonne Université, Observatoire de Paris, Université PSL, F-75005, Paris, France
| | - Julien Vincent
- Institut des Sciences Moléculaires d'Orsay (ISMO), Université Paris-Saclay, CNRS, 91405 Orsay, France
| | - Thomas Pino
- Institut des Sciences Moléculaires d'Orsay (ISMO), Université Paris-Saclay, CNRS, 91405 Orsay, France
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8
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Mackie CJ, Candian A, Lee TJ, Tielens AGGM. Anharmonicity and the IR Emission Spectrum of Neutral Interstellar PAH Molecules. J Phys Chem A 2022; 126:3198-3209. [PMID: 35544706 DOI: 10.1021/acs.jpca.2c01849] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
The characteristics of the CH stretching and out-of-plane bending modes in polycyclic aromatic hydrocarbon molecules are investigated using anharmonic density functional theory (DFT) coupled to a vibrational second-order perturbation treatment taking resonance effects into account. The results are used to calculate the infrared emission spectrum of vibrationally excited species in the collision-less environment of interstellar space. This model follows the energy cascade as the molecules relax after the absorption of a UV photon in order to calculate the detailed profiles of the infrared bands. The results are validated against elegant laboratory spectra of polycyclic aromatic hydrocarbon absorption and emission spectra obtained in molecular beams. The factors which influence the peak position, spectral detail, and relative strength of the CH stretching and out-of-plane bending modes are investigated, and detailed profiles for these modes are derived. These are compared to observations of astronomical objects in space, and the implications for our understanding of the characteristics of the molecular inventory of space are assessed.
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Affiliation(s)
- Cameron J Mackie
- Kenneth S. Pitzer Center for Theoretical Chemistry, Department of Chemistry, University of California, Berkeley, California 94720, United States.,Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Alessandra Candian
- van 't Hoff Institute for Molecular Science, University of Amsterdam, P.O. Box 94157, 1090 GD Amsterdam, The Netherlands
| | - Timothy J Lee
- NASA Ames Research Center, Moffett Field, California 94035-1000, United States
| | - Alexander G G M Tielens
- Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands.,Astronomy Department, University of Maryland, College Park, Maryland 20742, United States
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9
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Mackie CJ, Candian A, Lee TJ, Tielens AGGM. Modeling the infrared cascade spectra of small PAHs: the 11.2 μm band. Theor Chem Acc 2021; 140:124. [PMID: 34720707 PMCID: PMC8549957 DOI: 10.1007/s00214-021-02807-z] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2020] [Accepted: 07/02/2021] [Indexed: 11/18/2022]
Abstract
The profile of the 11.2 μm feature of the infrared (IR) cascade emission spectra of polycyclic aromatic hydrocarbon (PAH) molecules is investigated using a vibrational anharmonic method. Several factors are found to affect the profile including: the energy of the initially absorbed ultraviolet (UV) photon, the density of vibrational states, the anharmonic nature of the vibrational modes, the relative intensities of the vibrational modes, the rotational temperature of the molecule, and blending with nearby features. Each of these factors is explored independently and influence either the red or blue wing of the 11.2 μm feature. The majority impact solely the red wing, with the only factor altering the blue wing being the rotational temperature.
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Affiliation(s)
- Cameron J Mackie
- Kenneth S. Pitzer Center for Theoretical Chemistry Department of Chemistry, University of California, Berkeley, CA 94720 USA.,Lawrence Berkeley National Laboratory, Chemical Sciences Division, Berkeley, CA 94720 USA
| | - Alessandra Candian
- van 't Hoff Institute for Molecular Science, University of Amsterdam, P.O. Box 94157, 1090 GD Amsterdam, The Netherlands
| | - Timothy J Lee
- NASA Ames Research Center, Moffett Field, CA 94035-1000 USA
| | - Alexander G G M Tielens
- Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands.,Astronomy Department, University of Maryland, College Park, MD 20742 USA
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10
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McGill C, Forsuelo M, Guan Y, Green WH. Predicting Infrared Spectra with Message Passing Neural Networks. J Chem Inf Model 2021; 61:2594-2609. [PMID: 34048221 DOI: 10.1021/acs.jcim.1c00055] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Infrared (IR) spectroscopy remains an important tool for chemical characterization and identification. Chemprop-IR has been developed as a software package for the prediction of IR spectra through the use of machine learning. This work serves the dual purpose of providing a trained general-purpose model for the prediction of IR spectra with ease and providing the Chemprop-IR software framework for the training of new models. In Chemprop-IR, molecules are encoded using a directed message passing neural network, allowing for molecule latent representations to be learned and optimized for the task of spectral predictions. Model training incorporates spectra metrics and normalization techniques that offer better performance with spectral predictions than standard practice in regression models. The model makes use of pretraining using quantum chemistry calculations and ensembling of multiple submodels to improve generalizability and performance. The spectral predictions that result are of high quality, showing capability to capture the extreme diversity of spectral forms over chemical space and represent complex peak structures.
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Affiliation(s)
- Charles McGill
- Department of Chemical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States
| | - Michael Forsuelo
- Department of Chemical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States
| | - Yanfei Guan
- Department of Chemical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States
| | - William H Green
- Department of Chemical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States
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11
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Peeters E, Mackie C, Candian A, Tielens AGGM. A Spectroscopic View on Cosmic PAH Emission. Acc Chem Res 2021; 54:1921-1933. [PMID: 33780617 DOI: 10.1021/acs.accounts.0c00747] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
ConspectusPolycyclic aromatic hydrocarbon molecules (PAHs) are ubiquitously present at high abundances in the Universe. They are detected through their infrared (IR) fluorescence UV pumped by nearby massive stars. Hence, their infrared emission is used to determine the star formation rate in galaxies, one of the key indicators for understanding the evolution of galaxies. Together with fullerenes, PAHs are the largest molecules found in space. They significantly partake in a variety of physical and chemical processes in space, influencing star and planet formation as well as galaxy evolution.Since the IR features from PAHs originate from chemical bonds involving only nearest neighbor atoms, they have only a weak dependence on the size and structure of the molecule, and it is therefore not possible to identify the individual PAH molecules that make up the cosmic PAH family. This strongly hampers the interpretation of their astronomical fingerprints. Despite the lack of identification, constraints can be set on the characteristics of the cosmic PAH family thanks to a joint effort of astronomers, physicists, and chemists.This Account presents the spectroscopic properties of the cosmic PAH emission as well as the intrinsic spectroscopic properties of PAHs and astronomical modeling of the PAH evolution required for the interpretation of the cosmic PAH characteristics. We discuss the observed spectral signatures tracing PAH properties such as charge, size, and structure and highlight the related challenges. We discuss the recent success of anharmonic calculations of PAH infrared absorption and emission spectra and outline the path forward. Finally, we illustrate the importance of models on PAH processing for the interpretation of the astronomical data in terms of the charge balance and PAH destruction.Throughout this Account, we emphasize that huge progress is on the horizon on the astronomical front. Indeed, the world is eagerly awaiting the launch of the James Webb Space Telescope (JWST). With its incredible improvement in spatial resolution, combined with its complete spectral coverage of the PAH infrared emission bands at medium spectral resolution and superb sensitivity, the JWST will revolutionize PAH research. Previous observations could only present spectra averaged over regions with vastly different properties, thus greatly confusing their interpretation. The amazing spatial resolution of JWST will disentangle these different regions. This will allow us to quantify precisely how PAHs are modified by the physical conditions of their host environment and thus trace how PAHs evolve across space. However, this will only be achieved when the necessary (and still missing) fundamental properties of PAHs, outlined in this Account, are known. We strongly encourage you to join this effort.
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Affiliation(s)
- Els Peeters
- Department of Physics & Astronomy, University of Western Ontario, London, Ontario, Canada
- Institute for Earth and Space Exploration, University of Western Ontario, London, Ontario, Canada
- SETI Institute, 189 Bernardo Avenue, Suite 100, Mountain View, California 94043, United States
| | - Cameron Mackie
- Lawrence Berkeley National Laboratory, University of California, Berkeley, California 94720, United States
| | - Alessandra Candian
- van’t Hoff Institute for Molecular Sciences, University of Amsterdam, Amsterdam, The Netherlands
- Leiden Observatory, Leiden University, Leiden, The Netherlands
| | - Alexander G. G. M. Tielens
- Leiden Observatory, Leiden University, Leiden, The Netherlands
- University of Maryland, College Park, Maryland 20742, United States
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12
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Chakraborty S, Mulas G, Rapacioli M, Joblin C. Anharmonic Infrared Spectra of Thermally Excited Pyrene (C 16H 10): A Combined View of DFT-Based GVPT2 with AnharmonicCaOs, and Approximate DFT Molecular dynamics with DemonNano. JOURNAL OF MOLECULAR SPECTROSCOPY 2021; 378:111466. [PMID: 34257467 PMCID: PMC7611198 DOI: 10.1016/j.jms.2021.111466] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
The study of the Aromatic Infrared Bands (AIBs) in astronomical environments has opened interesting spectroscopic questions on the effect of anharmonicity on the infrared (IR) spectrum of hot polycyclic aromatic hydrocarbons (PAHs) and related species in isolated conditions. The forthcoming James Webb Space Telescope will unveil unprecedented spatial and spectral details in the AIB spectrum; significant advancement is thus necessary now to model the infrared emission of PAHs, their presumed carriers, with enough detail to exploit the information content of the AIBs. This requires including anharmonicity in such models, and to do so systematically for all species included, requiring a difficult compromise between accuracy and efficiency. We performed a benchmark study to compare the performances of two methods in calculating anharmonic spectra, comparing them to available experimental data. One is a full quantum method, AnharmoniCaOs, relying on an ab initio potential, and the other relies on Molecular Dynamics simulations using a Density Functional based Tight Binding potential. The first one is found to be very accurate and detailed, but it becomes computationally very expensive for increasing temperature; the second is faster and can be used for arbitrarily high temperatures, but is less accurate. Still, its results can be used to model the evolution with temperature of isolated bands. We propose a new recipe to model anharmonic AIB emission using minimal assumptions on the general behaviour of band positions and widths with temperature, which can be defined by a small number of empirical parameters. Modelling accuracy will depend critically on these empirical parameters, allowing for an incremental improvement in model results, as better estimates become gradually available.
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Affiliation(s)
- Shubhadip Chakraborty
- Institut de Recherche en Astrophysique et Planétologie, Université de Toulouse (UPS), CNRS, CNES, 9 Av. du Colonel Roche, 31028 Toulouse Cedex 4, France
| | - Giacomo Mulas
- Institut de Recherche en Astrophysique et Planétologie, Université de Toulouse (UPS), CNRS, CNES, 9 Av. du Colonel Roche, 31028 Toulouse Cedex 4, France
- Istituto Nazionale di Astrofisica (INAF), Osservatorio Astronomico di Cagliari, 09047 Selargius (CA), Italy
| | - Mathias Rapacioli
- Laboratoire de Chimie et Physique Quantiques (LCPQ/IRSAMC), Université de Toulouse (UPS),CNRS, 118 Route de Narbonne, 31062 Toulouse, France
| | - Christine Joblin
- Institut de Recherche en Astrophysique et Planétologie, Université de Toulouse (UPS), CNRS, CNES, 9 Av. du Colonel Roche, 31028 Toulouse Cedex 4, France
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13
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Geindre H, Allouche AR, Peláez D. Non long-range corrected density functionals incorrectly describe the intensity of the CH stretching band in polycyclic aromatic hydrocarbons. J Comput Chem 2021; 42:1018-1027. [PMID: 33760242 DOI: 10.1002/jcc.26520] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2020] [Revised: 02/24/2021] [Accepted: 02/26/2021] [Indexed: 11/12/2022]
Abstract
We present a comprehensive study of the most relevant numerical aspects influencing frequencies and intensities in the infrared spectrum of isolated polycyclic aromatic hydrocarbons (PAHs) regarding the overestimate of the IR CH-stretching bands. We use naphthalene as benchmark and show the validity of our results to different members of the PAH family. Our analysis relies on widely employed density functional theory methods and second-order vibrational perturbational theory for the computation of vibrational eigenstates. We have focused on the elucidation of the origin of the systematic overestimate of the intensities in the CH-stretching region. To rule out nonfundamental numerical errors, we have initially considered the influence of the electronic basis set and various other parameters on the different stages of the vibrational analysis. In a second stage, we have benchmarked the results of different density functional theory functionals with respect to the aforementioned overestimate taken as the ratio between the most prominent features of the spectrum, the CH-bending and the CH-stretching bands. Our results unambiguously indicate that the long-range correction plays a major role in this spurious numerical issue. More specifically, this phenomenon is due to an incorrect description of the charge distribution (and hence dipole) within the symmetrically relevant CH bonds. Long-range correction specifically remedies this issue. It improves the description of the intensities in the stretching region while at the same time it does not perturb significantly the rest of the spectrum. With respect to the frequencies, we have observed an overall improvement when compared to noncorrected functionals.
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Affiliation(s)
- Hugo Geindre
- Université Lille, UMR 8523 - Physique des Lasers, Atomes et Molécules, Lille, France
| | - Abdul-Rahman Allouche
- Institut Lumière Matière, UMR5306 Université Lyon 1-CNRS, Université de Lyon, Villeurbanne Cedex, France
| | - Daniel Peláez
- Institut des Sciences Moléculaires d'Orsay (ISMO) - UMR 8214. Bât. 520, Université Paris-Saclay, Orsay Cedex, France
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14
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Lemmens A, Rap DB, Thunnissen JMM, Gruet S, Steber AL, Panchagnula S, Tielens AGGM, Schnell M, Buma WJ, Rijs AM. Far-IR Absorption of Neutral Polycyclic Aromatic Hydrocarbons (PAHs): Light on the Mechanism of IR-UV Ion Dip Spectroscopy. J Phys Chem Lett 2020; 11:8997-9002. [PMID: 33035060 PMCID: PMC7649846 DOI: 10.1021/acs.jpclett.0c02714] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/17/2023]
Abstract
Gas-phase IR-UV double-resonance laser spectroscopy is an IR absorption technique that bridges the gap between experimental IR spectroscopy and theory. The IR experiments are used to directly evaluate predicted frequencies and potential energy surfaces as well as to probe the structure of isolated molecules. However, a detailed understanding of the underlying mechanisms is, especially in the far-IR regime, still far from complete, even though this is crucial for properly interpreting the recorded IR absorption spectra. Here, events occurring upon excitation to vibrational levels of polycyclic aromatic hydrocarbons by far-IR radiation from the FELIX free electron laser are followed using resonance-enhanced multiphoton ionization spectroscopy. These studies provide detailed insight into how ladder climbing and anharmonicity influence IR-UV spectroscopy and therefore the resulting IR signatures in the far-IR region. Moreover, the potential energy surfaces of these low-frequency delocalized modes are investigated and shown to have a strong harmonic character.
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Affiliation(s)
- Alexander
K. Lemmens
- Radboud
University, Institute for Molecules
and Materials, FELIX Laboratory, Toernooiveld 7, 6525 ED Nijmegen, The Netherlands
- University
of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
| | - Daniël B. Rap
- Radboud
University, Institute for Molecules
and Materials, FELIX Laboratory, Toernooiveld 7, 6525 ED Nijmegen, The Netherlands
| | - Johannes M. M. Thunnissen
- Radboud
University, Institute for Molecules
and Materials, FELIX Laboratory, Toernooiveld 7, 6525 ED Nijmegen, The Netherlands
| | - Sébastien Gruet
- Deutsches
Elektronen-Synchrotron, Notkestrasse 85, D-22607 Hamburg, Germany
- Institut
für Physikalische Chemie, Christian-Albrechts-Universität
zu Kiel, Max-Eyth-Strasse
1, D-24118 Kiel, Germany
| | - Amanda L. Steber
- Deutsches
Elektronen-Synchrotron, Notkestrasse 85, D-22607 Hamburg, Germany
- Institut
für Physikalische Chemie, Christian-Albrechts-Universität
zu Kiel, Max-Eyth-Strasse
1, D-24118 Kiel, Germany
| | - Sanjana Panchagnula
- Leiden
Observatory, Leiden University, Niels Bohrweg 2, 2333 CA Leiden, The Netherlands
| | | | - Melanie Schnell
- Deutsches
Elektronen-Synchrotron, Notkestrasse 85, D-22607 Hamburg, Germany
- Institut
für Physikalische Chemie, Christian-Albrechts-Universität
zu Kiel, Max-Eyth-Strasse
1, D-24118 Kiel, Germany
| | - Wybren Jan Buma
- Radboud
University, Institute for Molecules
and Materials, FELIX Laboratory, Toernooiveld 7, 6525 ED Nijmegen, The Netherlands
- University
of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
| | - Anouk M. Rijs
- Radboud
University, Institute for Molecules
and Materials, FELIX Laboratory, Toernooiveld 7, 6525 ED Nijmegen, The Netherlands
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15
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Sandford SA, Nuevo M, Bera PP, Lee TJ. Prebiotic Astrochemistry and the Formation of Molecules of Astrobiological Interest in Interstellar Clouds and Protostellar Disks. Chem Rev 2020; 120:4616-4659. [DOI: 10.1021/acs.chemrev.9b00560] [Citation(s) in RCA: 71] [Impact Index Per Article: 17.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Affiliation(s)
- Scott A. Sandford
- NASA Ames Research Center, MS 245-6, Moffett Field, California 94035, United States
| | - Michel Nuevo
- NASA Ames Research Center, MS 245-6, Moffett Field, California 94035, United States
- BAER Institute, NASA Research Park, MS 18-4, Moffett Field, California 94035, United States
| | - Partha P. Bera
- NASA Ames Research Center, MS 245-6, Moffett Field, California 94035, United States
- BAER Institute, NASA Research Park, MS 18-4, Moffett Field, California 94035, United States
| | - Timothy J. Lee
- NASA Ames Research Center, MS 245-3, Moffett Field, California 94035, United States
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