Unpicking vibration-vibration and vibration-torsion interactions in m-fluorotoluene

Davies, Alexander R.; Kemp, David J.; Wright, Timothy G.

doi:10.1016/j.jms.2021.111522

Cited by 6 publications

(2 citation statements)

References 25 publications

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“…This coupling need not occur at the initial energy redistribution step but must be present at some stage in the process to bring the increased density of states into play. Most recently, Wright and co-workers have explicitly explored the role of methyl torsion in coupling pathways in the excited electronic state for several substituted toluenes and N -methylpyrrole (NMP). − To rationalize the increase in IVR rate associated with the presence of methyl torsion, Moss et al proposed a torsion–vibration coupling model based on intramolecular van der Waals interactions . The interaction between torsion and the out-of-plane methyl wag that we have observed in toluene, , p -fluorotoluene, and m -fluorotoluene provides experimental evidence for a torsion–vibration coupling pathway that, because of the low frequency of the vibration, will be widespread among near-isoenergetic states in these molecules.…”

Section: Introductionmentioning

confidence: 72%

Strong Torsion–Vibration Interaction in N-Methylpyrrole Observed by Far-Infrared Spectroscopy

Gascooke

Lawrance

2022

J. Phys. Chem. A

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An interaction between methyl torsion and the lowlying 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, outof-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 Nmethylpyrrole. 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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Section: Introductionmentioning

confidence: 72%

Strong Torsion–Vibration Interaction in N-Methylpyrrole Observed by Far-Infrared Spectroscopy

Gascooke

Lawrance

2022

J. Phys. Chem. A

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“…For example, the frequencies of breathing vibration mode 1 for S 0 , D 0 , and S 1 of 2FBN measured in the experiment were 724 [ 18 ], 685, and 668 cm −1 , respectively; for mode 12, they were 835 [ 18 ], 823, and 815 cm −1 , respectively; for mode 18b, they were 1100 [ 18 ], 973, and 946 cm −1 , respectively. The reported experimental and theoretical data of mFBT and mDFB [ 47 ] also indicated that most of the vibrational modes of these two molecules followed this rule. Furthermore, from the above vibration data, we know that the frequency variation was larger for the out-of-plane mode (such as 18b of 2FBN) than for the in-plane mode (such as modes 1 and 12 of 2FBN).…”

Section: Discussionmentioning

confidence: 88%

Vibronic and Cationic Features of 2-Fluorobenzonitrile and 3-Fluorobenzonitrile Studied by REMPI and MATI Spectroscopy and Franck–Condon Simulations

Zhao

Jiao

et al. 2023

Molecules

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Fluorinated organic compounds have superior physicochemical properties than general organic compounds due to the strong C-F single bond; they are widely used in medicine, biology, pesticides, and materials science. In order to gain a deeper understanding of the physicochemical properties of fluorinated organic compounds, fluorinated aromatic compounds have been investigated by various spectroscopic techniques. 2-fluorobenzonitrile and 3-fluorobenzonitrile are important fine chemical intermediates and their excited state S1 and cationic ground state D0 vibrational features remain unknown. In this paper, we used two-color resonance two photon ionization (2-color REMPI) and mass analyzed threshold ionization (MATI) spectroscopy to study S1 and D0 state vibrational features of 2-fluorobenzonitrile and 3-fluorobenzonitrile. The precise excitation energy (band origin) and adiabatic ionization energy were determined to be 36,028 ± 2 cm−1 and 78,650 ± 5 cm−1 for 2-fluorobenzonitrile and 35,989 ± 2 cm−1 and 78,873 ± 5 cm−1 for 3-fluorobenzonitrile, respectively. The density functional theory (DFT) at the levels of RB3LYP/aug-cc-pvtz, TD-B3LYP/aug-cc-pvtz, and UB3LYP/aug-cc-pvtz were used to calculate the stable structures and vibrational frequencies for the ground state S0, excited state S1, and cationic ground state D0, respectively. Franck–Condon spectral simulations for transitions of S1 ← S0 and D0 ← S1 were performed based on the above DFT calculations. The theoretical and experimental results were in good agreement. The observed vibrational features in S1 and D0 states were assigned according to the simulated spectra and the comparison with structurally similar molecules. Several experimental findings and molecular features were discussed in detail.

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Valence and Rydberg excitations of 2-fluorotoluene in the 4.4–10.8 eV photoabsorption energy region

Randi¹,

Kumar²,

Lozano³

et al. 2023

Journal of Quantitative Spectroscopy and Radiative Transfer

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Unpicking vibration-vibration and vibration-torsion interactions in m-fluorotoluene

Cited by 6 publications

References 25 publications

Strong Torsion–Vibration Interaction in N-Methylpyrrole Observed by Far-Infrared Spectroscopy

Strong Torsion–Vibration Interaction in N-Methylpyrrole Observed by Far-Infrared Spectroscopy

Vibronic and Cationic Features of 2-Fluorobenzonitrile and 3-Fluorobenzonitrile Studied by REMPI and MATI Spectroscopy and Franck–Condon Simulations

Valence and Rydberg excitations of 2-fluorotoluene in the 4.4–10.8 eV photoabsorption energy region

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