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Barth M, Kleiner I, Nguyen HVL. Coupled internal rotations and 14N quadrupole hyperfine structure of 2,4-dimethylpyrrole investigated by microwave spectroscopy and quantum chemistry. J Chem Phys 2024; 160:244303. [PMID: 38912676 DOI: 10.1063/5.0213319] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2024] [Accepted: 05/31/2024] [Indexed: 06/25/2024] Open
Abstract
The microwave spectrum of 2,4-dimethylpyrrole was investigated using a Fourier-transform microwave spectrometer in a supersonic expansion. Torsional splittings arising from two inequivalent methyl internal rotors in combination with hyperfine splittings due to the nuclear quadrupole coupling of the 14N nucleus were observed. The experiments were accompanied by quantum chemical calculations. A total of 1561 rotational lines were assigned and fitted in global fits using the programs XIAM and BELGI-Cs-2Tops-hyperfine, both achieved the measurement accuracy of 4 kHz. Local separate fits were also performed to verify the correctness of the assignment. Accurate experimental molecular and internal rotation parameters could be deduced and compared to the calculated ones. The barrier to internal rotation of the 2-methyl rotor was determined to be 277.830(26) cm-1, essentially the same as the value of about 280 cm-1 found for 2-methylpyrrole but lower than the value of 317 cm-1 found for 2,5-dimethylpyrrole. The torsional barrier value of the 4-methyl rotor is 262.210(27) cm-1, slightly higher than the value of 246 cm-1 found for 3-methylpyrrole. Benchmarking the rotational constants for 2,4- and 2,5-dimethylpyrrole revealed that the MP2/6-31G(d,p) level could be helpful to guide the assignment of microwave spectra of pyrrole derivatives.
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Affiliation(s)
- Mike Barth
- Univ Paris Est Creteil and Université Paris Cité, CNRS, LISA, F-94010 Créteil, France
| | - Isabelle Kleiner
- Université Paris Cité and Univ Paris Est Creteil, CNRS, LISA, F-75013 Paris, France
| | - Ha Vinh Lam Nguyen
- Univ Paris Est Creteil and Université Paris Cité, CNRS, LISA, F-94010 Créteil, France
- Institut Universitaire de France (IUF), 1 rue Descartes, F-75231 Paris, France
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Antonelli E, Gougoula E, Walker NR, Schwell M, Nguyen HVL, Kleiner I. A global rho-axis method for fitting asymmetric tops with one methyl internal rotor and two 14N nuclei: Application of BELGI-2N to the microwave spectra of four methylimidazole isomers. J Chem Phys 2024; 160:214309. [PMID: 38836784 DOI: 10.1063/5.0207944] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2024] [Accepted: 05/08/2024] [Indexed: 06/06/2024] Open
Abstract
A number of internal rotation codes can deal with the combination of one or two internal rotors with one 14N quadrupole nucleus, but once it comes to two 14N nuclei, no such code is available even for the case of one internal rotor. We present here the extension of our internal rotor program called BELGI-2N using the rho-axis method global approach to deal with compounds containing one methyl rotor and two weakly coupling 14N nuclei. To test our new code, we applied it to the microwave data recorded for N-methylimidazole, 2-methylimidazole, 4-methylimidazole, and 5-methylimidazole using a chirped-pulse Fourier transform microwave spectrometer in the 7.0-18.5 GHz frequency range. Compared to the previously published study, BELGI-2N was able to (i) significantly increase the number of assigned and fitted lines, (ii) fit the complete datasets considering both the internal rotation and the 14N nuclear quadrupole coupling effects simultaneously, and (iii) achieve standard deviations within the measurement accuracy for all methylimidazole isomers.
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Affiliation(s)
- Eléonore Antonelli
- Univ Paris Est Creteil and Université Paris Cité, CNRS, LISA, F-94010 Créteil, France
| | - Eva Gougoula
- Chemistry, School of Natural and Environmental Sciences, Newcastle University, Bedson Building, Newcastle Upon Tyne NE1 7RU, United Kingdom
| | - Nicholas R Walker
- Chemistry, School of Natural and Environmental Sciences, Newcastle University, Bedson Building, Newcastle Upon Tyne NE1 7RU, United Kingdom
| | - Martin Schwell
- Univ Paris Est Creteil and Université Paris Cité, CNRS, LISA, F-94010 Créteil, France
| | - Ha Vinh Lam Nguyen
- Univ Paris Est Creteil and Université Paris Cité, CNRS, LISA, F-94010 Créteil, France
- Institut Universitaire de France (IUF), F-75231 Paris, France
| | - Isabelle Kleiner
- Université Paris Cité and Univ Paris Est Creteil, CNRS, LISA, F-75013 Paris, France
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Hadki HE, Koziol KJ, Kabbaj OK, Komiha N, Kleiner I, Nguyen HVL. The Microwave Rotational Electric Resonance (RER) Spectrum of Benzothiazole. Molecules 2023; 28:molecules28083419. [PMID: 37110653 PMCID: PMC10146593 DOI: 10.3390/molecules28083419] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2023] [Revised: 04/04/2023] [Accepted: 04/06/2023] [Indexed: 04/29/2023] Open
Abstract
The microwave spectra of benzothiazole were measured in the frequency range 2-26.5 GHz using a pulsed molecular jet Fourier transform microwave spectrometer. Hyperfine splittings arising from the quadrupole coupling of the 14N nucleus were fully resolved and analyzed simultaneously with the rotational frequencies. In total, 194 and 92 hyperfine components of the main species and the 34S isotopologue, respectively, were measured and fitted to measurement accuracy using a semi-rigid rotor model supplemented by a Hamiltonian accounting for the 14N nuclear quadrupole coupling effect. Highly accurate rotational constants, centrifugal distortion constants, and 14N nuclear quadrupole coupling constants were deduced. A large number of method and basis set combinations were used to optimize the molecular geometry of benzothiazole, and the calculated rotational constants were compared with the experimentally determined constants in the course of a benchmarking effort. The similar value of the χcc quadrupole coupling constant when compared to other thiazole derivatives indicates only very small changes of the electronic environment at the nitrogen nucleus in these compounds. The small negative inertial defect of -0.056 uÅ2 hints that low-frequency out-of-plane vibrations are present in benzothiazole, similar to the observation for some other planar aromatic molecules.
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Affiliation(s)
- Hamza El Hadki
- Laboratory of Spectroscopy, Molecular Modeling, Materials, Nanomaterials, Water, and Environment, Faculty of Sciences, Mohammed V University, Av Ibn Battouta, Rabat B.P. 1014, Morocco
- Univ Paris Est Creteil and Université Paris Cité, CNRS, LISA, 94010 Créteil, France
| | - Kenneth J Koziol
- Univ Paris Est Creteil and Université Paris Cité, CNRS, LISA, 94010 Créteil, France
| | - Oum Keltoum Kabbaj
- Laboratory of Spectroscopy, Molecular Modeling, Materials, Nanomaterials, Water, and Environment, Faculty of Sciences, Mohammed V University, Av Ibn Battouta, Rabat B.P. 1014, Morocco
| | - Najia Komiha
- Laboratory of Spectroscopy, Molecular Modeling, Materials, Nanomaterials, Water, and Environment, Faculty of Sciences, Mohammed V University, Av Ibn Battouta, Rabat B.P. 1014, Morocco
| | - Isabelle Kleiner
- Université Paris Cité and Univ Paris Est Creteil, CNRS, LISA, 75013 Paris, France
| | - Ha Vinh Lam Nguyen
- Univ Paris Est Creteil and Université Paris Cité, CNRS, LISA, 94010 Créteil, France
- Institut Universitaire de France (IUF), 75231 Paris, France
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Wang K, He X, Rong C, Zhong A, Liu S, Zhao D. On the origin and nature of internal methyl rotation barriers: an information-theoretic approach study. Theor Chem Acc 2022. [DOI: 10.1007/s00214-022-02910-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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Tyuterev V, Tashkun S, Rey M, Nikitin A. High-order contact transformations of molecular Hamiltonians: general approach, fast computational algorithm and convergence of ro-vibrational polyad models. Mol Phys 2022. [DOI: 10.1080/00268976.2022.2096140] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
Affiliation(s)
- Vladimir Tyuterev
- Groupe de Spectrométrie Moléculaire et Atmosphérique, Université de Reims, Reims, France
- Laboratory of Molecular Quantum Mechanics and Radiative Transfer, Tomsk State University, Tomsk, Russia
| | - Sergey Tashkun
- Laboratory of Theoretical Spectroscopy, V.E. Zuev Institute of Atmospheric Optics, Siberian Branch, Russian Academy of Sciences, Tomsk, Russia
| | - Michael Rey
- Groupe de Spectrométrie Moléculaire et Atmosphérique, Université de Reims, Reims, France
| | - Andrei Nikitin
- Laboratory of Theoretical Spectroscopy, V.E. Zuev Institute of Atmospheric Optics, Siberian Branch, Russian Academy of Sciences, Tomsk, Russia
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Nguyen HVL, Caminati W, Grabow JU. The LAM of the Rings: Large Amplitude Motions in Aromatic Molecules Studied by Microwave Spectroscopy. Molecules 2022; 27:3948. [PMID: 35745072 PMCID: PMC9230607 DOI: 10.3390/molecules27123948] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2022] [Revised: 05/27/2022] [Accepted: 06/06/2022] [Indexed: 11/17/2022] Open
Abstract
Large amplitude motions (LAMs) form a fundamental phenomenon that demands the development of specific theoretical and Hamiltonian models. In recent years, along with the strong progress in instrumental techniques on high-resolution microwave spectroscopy and computational capacity in quantum chemistry, studies on LAMs have become very diverse. Larger and more complex molecular systems have been taken under investigation, ranging from series of heteroaromatic molecules from five- and six-membered rings to polycyclic-aromatic-hydrocarbon derivatives. Such systems are ideally suited to create families of molecules in which the positions and the number of LAMs can be varied, while the heteroatoms often provide a sufficient dipole moment to the systems to warrant the observation of their rotational spectra. This review will summarize three types of LAMs: internal rotation, inversion tunneling, and ring puckering, which are frequently observed in aromatic five-membered rings such as furan, thiophene, pyrrole, thiazole, and oxazole derivatives, in aromatic six-membered rings such as benzene, pyridine, and pyrimidine derivatives, and larger combined rings such as naphthalene, indole, and indan derivatives. For each molecular class, we will present the representatives and summarize the recent insights on the molecular structure and internal dynamics and how they help to advance the field of quantum mechanics.
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Affiliation(s)
- Ha Vinh Lam Nguyen
- Univ Paris Est Creteil and Université Paris Cité, CNRS, LISA, F-94010 Créteil, France
- Institut Universitaire de France (IUF), F-75231 Paris, France
| | - Walther Caminati
- Departimento di Chimica ‘G. Ciamican’, Universita degli Studi di Bologna, Via Selmi 2, 40126 Bologna, Italy;
| | - Jens-Uwe Grabow
- Institut für Physikalische Chemie und Elektrochemie, Gottfried-Wilhelm-Leibniz-Universität Hannover, Callinstraße 3A, 30167 Hannover, Germany
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Bruckhuisen J, Chawananon S, Kleiner I, Roucou A, Dhont G, Bracquart C, Asselin P, Cuisset A. Millimeter-Wave Spectroscopy of Methylfuran Isomers: Local vs. Global Treatments of the Internal Rotation. MOLECULES (BASEL, SWITZERLAND) 2022; 27:molecules27113591. [PMID: 35684523 PMCID: PMC9182110 DOI: 10.3390/molecules27113591] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/29/2022] [Revised: 05/22/2022] [Accepted: 05/25/2022] [Indexed: 11/22/2022]
Abstract
Methylfurans are methylated aromatic heterocyclic volatile organic compounds and primary or secondary pollutants in the atmosphere due to their capability to form secondary organic aerosols in presence of atmospheric oxidants. There is therefore a significant interest to monitor these molecules in the gas phase. High resolution spectroscopic studies of methylated furan compounds are generally limited to pure rotational spectroscopy in the vibrational ground state. This lack of results might be explained by the difficulties arisen from the internal rotation of the methyl group inducing non-trivial patterns in the rotational spectra. In this study, we discuss the benefits to assign the mm-wave rotational-torsional spectra of methylfuran with the global approach of the BELGI-Cs code compared to local approaches such as XIAM and ERHAM. The global approach reproduces the observed rotational lines of 2-methylfuran and 3-methylfuran in the mm-wave region at the experimental accuracy for the ground vt=0 and the first torsional vt=1 states with a unique set of molecular parameters. In addition, the V3 and V6 parameters describing the internal rotation potential barrier may be determined with a high degree of accuracy with the global approach. Finally, a discussion with other heterocyclic compounds enables the study of the influence of the electronic environment on the hindered rotation of the methyl group.
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Affiliation(s)
- Jonas Bruckhuisen
- LPCA, Laboratoire de Physico-Chimie de l’Atmosphère, Université du Littoral Côte d’Opale, UR4493, F-59140 Dunkerque, France; (J.B.); (A.R.); (G.D.); (C.B.)
| | - Sathapana Chawananon
- CNRS, MONARIS, UMR8233, Sorbonne gé, 4 Pl Jussieu, F-75005 Paris, France; (S.C.); (P.A.)
| | - Isabelle Kleiner
- CNRS UMR 7583, Laboratoire Interuniversitaire des Systèmes Atmosphériques, Université Paris Cité and Université Paris Est Créteil, F-75013 Paris, France;
| | - Anthony Roucou
- LPCA, Laboratoire de Physico-Chimie de l’Atmosphère, Université du Littoral Côte d’Opale, UR4493, F-59140 Dunkerque, France; (J.B.); (A.R.); (G.D.); (C.B.)
| | - Guillaume Dhont
- LPCA, Laboratoire de Physico-Chimie de l’Atmosphère, Université du Littoral Côte d’Opale, UR4493, F-59140 Dunkerque, France; (J.B.); (A.R.); (G.D.); (C.B.)
| | - Colwyn Bracquart
- LPCA, Laboratoire de Physico-Chimie de l’Atmosphère, Université du Littoral Côte d’Opale, UR4493, F-59140 Dunkerque, France; (J.B.); (A.R.); (G.D.); (C.B.)
| | - Pierre Asselin
- CNRS, MONARIS, UMR8233, Sorbonne gé, 4 Pl Jussieu, F-75005 Paris, France; (S.C.); (P.A.)
| | - Arnaud Cuisset
- LPCA, Laboratoire de Physico-Chimie de l’Atmosphère, Université du Littoral Côte d’Opale, UR4493, F-59140 Dunkerque, France; (J.B.); (A.R.); (G.D.); (C.B.)
- Correspondence:
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Skeletal Torsion Tunneling and Methyl Internal Rotation: The Coupled Large Amplitude Motions in Phenyl Acetate. Molecules 2022; 27:molecules27092730. [PMID: 35566082 PMCID: PMC9105391 DOI: 10.3390/molecules27092730] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2022] [Revised: 04/17/2022] [Accepted: 04/19/2022] [Indexed: 02/05/2023] Open
Abstract
The rotational spectrum of phenyl acetate, CH3COOC6H5, is measured using a free jet absorption millimeter-wave spectrometer in the range from 60 to 78 GHz and two pulsed jet Fourier transform microwave spectrometers covering a total frequency range from 2 to 26.5 GHz. The features of two large amplitude motions, the methyl group internal rotation and the skeletal torsion of the CH3COO group with respect to the phenyl ring C6H5 (tilted at about 70°), characterize the spectrum. The vibrational ground state is split into four widely spaced sublevels, labeled as A0, E0, A1, and E1, each of them with its set of rotational transitions and with additional interstate transitions. A global fit of the line frequencies of the four sublevels leads to the determination of 51 spectroscopic parameters, including the ΔEA0/A1 and ΔEE0/E1 vibrational splittings of ~36.4 and ~33.5 GHz, respectively. The V3 barrier to methyl internal rotation (~136 cm−1) and the skeletal torsion B2 barrier to the orthogonality of the two planes (~68 cm−1) are deduced.
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Khemissi S, Schwell M, Kleiner I, Nguyen HVL. Influence of π-electron conjugation outside the aromatic ring on the methyl internal rotation of 4-methyl-5-vinylthiazole. Mol Phys 2022. [DOI: 10.1080/00268976.2022.2052372] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Affiliation(s)
- Safa Khemissi
- Univ Paris Est Creteil and Université Paris Cité, CNRS, LISA, Créteil, France
| | - Martin Schwell
- Univ Paris Est Creteil and Université Paris Cité, CNRS, LISA, Créteil, France
| | - Isabelle Kleiner
- Université Paris Cité and Univ Paris Est Creteil, CNRS, LISA, Paris, France
| | - Ha Vinh Lam Nguyen
- Univ Paris Est Creteil and Université Paris Cité, CNRS, LISA, Créteil, France
- Institut Universitaire de France (IUF), Paris, France
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Dindić C, Nguyen HVL. Microwave Spectrum of Two-Top Molecule: 2-Acetyl-3-Methylthiophene. Chemphyschem 2021; 22:2420-2428. [PMID: 34546633 DOI: 10.1002/cphc.202100514] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2021] [Revised: 08/19/2021] [Indexed: 11/06/2022]
Abstract
The microwave spectrum of 2-acetyl-3-methylthiophene (2A3MT) was recorded in the frequency range from 2 to 26.5 GHz using a molecular jet Fourier transform microwave spectrometer and could be fully assigned to the anti-conformer of the molecule, while the syn-conformer was not observable. Torsional splittings of all rotational transitions in quintets due to internal rotations of the acetyl methyl and the ring methyl groups were resolved and analyzed, yielding barriers to internal rotation of 306.184(46) cm-1 and 321.813(64) cm-1 , respectively. The rotational and centrifugal distortion constants were determined with high accuracy, and the experimental values are compared to those derived from quantum chemical calculations. The experimentally determined inertial defect supports the conclusion that anti-2A3MT is planar, even though a number of MP2 calculations predicted the contrary.
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Affiliation(s)
- Christina Dindić
- Institute of Physical Chemistry, RWTH Aachen University, Landoltweg 2, 52074, Aachen, Germany
| | - Ha Vinh Lam Nguyen
- Univ Paris Est Creteil and Université de Paris, CNRS, LISA, 94010, Créteil, France.,Institut Universitaire de France (IUF), 75231, Paris cedex 05, France
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