Tunneling motion and splitting in the CH2OH radical: (Sub-)millimeter wave spectrum analysis
- 23 June 2022
- journal article
- research article
- Published by AIP Publishing in The Journal of Chemical Physics
- Vol. 156 (24), 244301
- https://doi.org/10.1063/5.0095242
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 & ANGLE;H1COH and & ANGLE;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. Published under an exclusive license by AIP Publishing.Funding Information
- Laboratoire d'excellence Physique Atomes Lumière Matière (ANR-10-LABX-0039-PALM)
- Agence Nationale de la Recherche (ANR-19-CE30-0017-01)
- Institut national des sciences de l'Univers (PCMI)
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