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Gascooke JR, Lawrance WD. Strong Torsion-Vibration Interaction in N-Methylpyrrole Observed by Far-Infrared Spectroscopy. J Phys Chem A 2022; 126:2160-2169. [PMID: 35357831 DOI: 10.1021/acs.jpca.1c10636] [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
An interaction between methyl torsion and the low-lying out-of-plane methyl wag vibration has been observed in toluene, p-fluorotoluene, and m-fluorotoluene, contravening the traditional assumption used when analyzing spectra that methyl torsion can be treated independently of the small-amplitude vibrations. When a methyl group is attached to a planar frame, out-of-plane methyl wag vibrations always occur, and hence this type of interaction between methyl torsion and vibration is potentially extensive. To probe whether this coupling occurs beyond toluene and its derivatives, we have studied the far-infrared absorption band for the out-of-plane methyl wagging mode in N-methylpyrrole. The torsional sequence structure reveals a particularly strong torsion-vibration interaction. Spectral simulations yield a torsion-vibration coupling matrix element of 34.0 cm-1, over twice the value for toluene. The large torsion-vibration coupling constant implies that there is a significant tilting of the methyl group out of plane. Quantum chemistry calculations reveal a much larger out-of-plane methyl tilt angle in N-methylpyrrole compared to toluene, qualitatively consistent with this expectation. This is the first nontoluene derivative for which this type of torsion-vibration interaction has been reported and shows that the effect extends beyond toluenes. When present, this interaction links small-amplitude vibrations to the methyl torsion, providing a mechanism to bring the increased density of states into play and accelerate the rate of intramolecular vibrational energy redistribution.
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Affiliation(s)
- Jason R Gascooke
- College of Science and Engineering, Flinders University, GPO Box 2100, Adelaide, SA 5001, Australia
| | - Warren D Lawrance
- College of Science and Engineering, Flinders University, GPO Box 2100, Adelaide, SA 5001, Australia
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Gascooke JR, Appadoo D, Lawrance WD. Torsion-vibration interactions determined from (far) infrared spectra. J Chem Phys 2021; 155:124306. [PMID: 34598554 DOI: 10.1063/5.0062070] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Observations of the torsional and low-lying vibrational-torsional states of toluene, p-fluorotoluene, and m-fluorotoluene using the technique of two dimensional laser induced fluorescence (2D-LIF) have revealed interactions between the methyl torsion and low frequency out-of-plane methyl wagging vibration. These interactions can change the values of constants extracted from the analysis of rotational spectra, which usually assume that the large amplitude torsional motion can be treated independent of the small amplitude vibrations. Since out-of-plane methyl wagging modes will be present whenever a methyl group is attached to a planar frame, this type of torsion-vibration interaction is potentially widespread; it is thus important to establish the extent and strength of this type of interaction. 2D-LIF is limited to molecules that fluoresce from excited electronic states, and to explore interactions between torsion and methyl wagging vibrations in a wide range of molecules necessitates developing alternative experimental approaches. Infrared absorption spectroscopy is one such approach. It is shown that for the low torsional barrier case, the torsional sequence bands accompanying the out-of-plane methyl wagging transition provide a sensitive probe of the interaction. As an illustration, the far infrared absorption spectrum of toluene in the region of the M20 band (∼205 cm-1) is presented and analyzed. The torsional sequence structure provides insight into the higher torsional states (up to m = 7) in the ground vibrational state and M20. An analysis of these bands enables the torsion-vibration coupling and torsional constants to be extracted. A general method to analyze such spectra is presented.
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Affiliation(s)
- Jason R Gascooke
- College of Science and Engineering, Flinders University, GPO Box 2100, Adelaide, SA 5001, Australia
| | - Dominique Appadoo
- Australian Synchrotron, 800 Blackburn Road, Clayton, VIC 3168, Australia
| | - Warren D Lawrance
- College of Science and Engineering, Flinders University, GPO Box 2100, Adelaide, SA 5001, Australia
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Roucou A, Goubet M, Kleiner I, Bteich S, Cuisset A. Large Amplitude Torsions in Nitrotoluene Isomers Studied by Rotational Spectroscopy and Quantum Chemistry Calculations. Chemphyschem 2020; 21:2523-2538. [PMID: 32857456 DOI: 10.1002/cphc.202000591] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2020] [Revised: 08/27/2020] [Indexed: 11/12/2022]
Abstract
Rotational spectra of ortho-nitrotoluene (2-NT) and para-nitrotoluene (4-NT) have been recorded at low and room temperatures using a supersonic jet Fourier Transform microwave (MW) spectrometer and a millimeter-wave frequency multiplier chain, respectively. Supported by quantum chemistry calculations, the spectral analysis of pure rotation lines in the vibrational ground state has allowed to characterise the rotational energy, the hyperfine structure due to the 14 N nucleus and the internal rotation splittings arising from the methyl group. For 2-NT, an anisotropic internal rotation of coupled -CH3 and -NO2 torsional motions was identified by quantum chemistry calculations and discussed from the results of the MW analysis. The study of the internal rotation splittings in the spectra of three NT isomers allowed to characterise the internal rotation potentials of the methyl group and to compare them with other mono-substituted toluene derivatives in order to study the isomeric influence on the internal rotation barrier.
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Affiliation(s)
- Anthony Roucou
- Université du Littoral Côte d'Opale, UR 4493, LPCA, Laboratoire de Physico-Chimie de l'Atmosphère, F-59140, Dunkerque, France.,Institut de la Matière Condensée et des Nanosciences (IMCN), Université catholique de Louvain, Chemin du Cyclotron 2, 1348, Louvain-la-Neuve, Belgium
| | - Manuel Goubet
- Univ. Lille, CNRS, UMR8523 - PhLAM - Physique des Lasers Atomes et Molécules, F-59000, Lille, France
| | - Isabelle Kleiner
- Laboratoire Interuniversitaire des Systèmes Atmosphériques (LISA), CNRS UMR 7583, Université Paris-Est Créteil & Université de Paris, Institut Pierre Simon Laplace (IPSL), 61 avenue du Général de Gaulle, F-94010, Créteil cedex, France
| | - Sabath Bteich
- Université du Littoral Côte d'Opale, UR 4493, LPCA, Laboratoire de Physico-Chimie de l'Atmosphère, F-59140, Dunkerque, France
| | - Arnaud Cuisset
- Université du Littoral Côte d'Opale, UR 4493, LPCA, Laboratoire de Physico-Chimie de l'Atmosphère, F-59140, Dunkerque, France
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Ruiz-Santoyo JA, Torres-Boy AY, Minguela-Gallardo JA, Yi JT, Romero-Servín SA, Pratt DW, Álvarez-Valtierra L. Rotationally resolved electronic spectrum of N-Methylcarbazole in the gas phase: A study of methyl group internal rotation. J Mol Struct 2020. [DOI: 10.1016/j.molstruc.2020.128282] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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Davies AR, Kemp DJ, Warner LG, Fryer EF, Rees A, Wright TG. Variations in Duschinsky rotations in m-fluorotoluene and m-chlorotoluene during excitation and ionization. J Chem Phys 2020; 152:214303. [DOI: 10.1063/5.0009391] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Alexander R. Davies
- School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom
| | - David J. Kemp
- School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom
| | - Lewis G. Warner
- School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom
| | - Elizabeth F. Fryer
- School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom
| | - Alan Rees
- School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom
| | - Timothy G. Wright
- School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom
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Kemp DJ, Warner LG, Wright TG. Torsions, low-frequency vibrations, and vibration–torsion (“vibtor”) levels in the m-chlorotoluene cation. J Chem Phys 2020; 152:064303. [DOI: 10.1063/1.5142992] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- David J. Kemp
- School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom
| | - Lewis G. Warner
- School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom
| | - Timothy G. Wright
- School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom
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Camiruaga A, Usabiaga I, D'mello VC, García GA, Wategaonkar S, Fernández JA. Revisiting the spectroscopy of xanthine derivatives: theobromine and theophylline. Phys Chem Chem Phys 2019; 21:26430-26437. [PMID: 31774088 DOI: 10.1039/c9cp05068j] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We explore the influence of the relative position of the methyl substituent on the photophysics of theophylline and theobromine, two molecules that are structurally related to the DNA bases. Using a combination of spectroscopic techniques and quantum mechanical calculations, we show that moving the methyl group from N1 in theophylline to N7 in theobromine causes significant differences in their excited state properties, i.e., it produces pyramidalization of N7 in the excited state of the latter. Paradoxically, this modification seems to have little effect on the structural properties of the cation and the ionization process. It is suggested that similar effects may exist in the excited state properties of DNA bases.
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Affiliation(s)
- Ander Camiruaga
- Dep. of Physical Chemistry, Faculty of Science and Technology, University of the Basque Country (UPV/EHU), Barrio Sarriena s/n, Leioa 48940, Spain.
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Gardner AM, Whalley LE, Kemp DJ, Tuttle WD, Wright TG. Identification of separate isoenergetic routes for vibrational energy flow in p-fluorotoluene. J Chem Phys 2019; 151:154302. [DOI: 10.1063/1.5126179] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Adrian M. Gardner
- School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom
| | - Laura E. Whalley
- School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom
| | - David J. Kemp
- School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom
| | - William D. Tuttle
- School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom
| | - Timothy G. Wright
- School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom
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Kemp DJ, Fryer EF, Davies AR, Wright TG. Vibration-modified torsional potentials and vibration-torsion (“vibtor”) levels in them-fluorotoluene cation. J Chem Phys 2019; 151:084311. [DOI: 10.1063/1.5116520] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- David J. Kemp
- School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom
| | - Elizabeth F. Fryer
- School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom
| | - Alexander R. Davies
- School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom
| | - Timothy G. Wright
- School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom
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