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Tunneling motion and splitting in the CH2OH radical: (Sub-)millimeter wave spectrum analysis

Abstract : The (sub-)millimeter wave spectrum of the non-rigid CH2OH radical is investigated both experimentally and theoretically. Ab initio calculations are carried out to quantitatively characterize its potential energy surface as a function of the two large amplitude ∠H1COH and ∠H2COH dihedral angles. It is shown that the radical displays a large amplitude torsional-like motion of its CH2 group with respect to the OH group. The rotation–torsion levels computed with the help of a 4D Hamiltonian accounting for this torsional-like motion and for the overall rotation exhibit a tunneling splitting, in agreement with recent experimental investigations, and a strong rotational dependence of this tunneling splitting on the rotational quantum number K a due to the rotation–torsion Coriolis coupling. Based on an internal axis method approach, a fitting Hamiltonian accounting for tunneling effects and for the fine and hyperfine structure is built and applied to the fitting of the new (sub)-millimeter wave transitions measured in this work along with previously available high-resolution data. 778 frequencies and wavenumbers are reproduced with a unitless standard deviation of 0.79 using 27 parameters. The N = 0 tunneling splitting, which could not be determined unambiguously in the previous high-resolution investigations, is determined based on its rotational dependence.
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https://hal.archives-ouvertes.fr/hal-03726378
Contributor : Marie-Aline Martin-Drumel Connect in order to contact the contributor
Submitted on : Monday, July 18, 2022 - 2:50:37 PM
Last modification on : Friday, November 18, 2022 - 4:12:30 AM

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L. Coudert, O. Chitarra, J.-T. Spaniol, J.-C. Loison, M.-A. Martin-Drumel, et al.. Tunneling motion and splitting in the CH2OH radical: (Sub-)millimeter wave spectrum analysis. Journal of Chemical Physics, 2022, 156 (24), pp.244301. ⟨10.1063/5.0095242⟩. ⟨hal-03726378⟩

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