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 Title: Analysis Of The Ch2oh Radical Spectrum With An Iam Tunneling Approach Author(s): Coudert, L.H. Contributor(s): Loison, J.-C.; Pirali, Olivier; Martin-Drumel, Marie-Aline; Spaniol, Jean-Thibaut; Chitarra, Olivia Subject(s): Astronomy Abstract: Early {\em ab initio} calculations\footnote{Saeb\o, Radom, and Schaefer, {\em J.\ Chem.\ Phys.}~{\bf 78} (1983) 845; Marenich and Boggs, {\em J.\ Chem.\ Phys.}~{\bf 119} (2003) 3098; and Ibid., {\em J.\ Chem.\ Phys.}~{\bf 119} (2003) 10105} revealed that the hydroxymethyl radical (\ce{CH2OH}) is a non-rigid species exhibiting a complicated potential energy surface. It displays 4 $C_1$ non-superimposable, energetically equivalent, equilibrium configurations and 4 $C_s$ maxima, approximately 300 and 1500\,cm$^{-1}$ above the equilibrium configurations. The large amplitude motion of the radical can be pictured as an internal rotation of the \ce{CH2} group with respect to the \ce{OH} group. The axis of internal rotation is the \ce{CO} bond and the two-fold symmetry hindering potential is characterized by a barrier height of 1500\,cm$^{-1}$. Aided by new {\em ab initio} results, the torsional levels associated with this torsional motion were computed. The energy levels display a tunneling splitting which, for the ground torsional level, was found to be smaller than 0.1~cm$^{-1}$. As the large amplitude motion of the hydroxymethyl radical seems to be well described by the high barrier approximation, the tunneling IAM water dimer formalism\footnote{Hougen, {\em J.\ Mol.\ Spectrosc.}~{\bf 114} (1985) 395; and Coudert and Hougen, {\em J.\ Mol.\ Spectrosc.}~{\bf 130} (1988) 86} was used to derive a fitting approach aimed at accounting for its rotation-tunneling energy. The effects of the fine spin-rotation and hyperfine spin-spin couplings were also included since there is an unpaired electron. In the paper, the analysis with the IAM approach$^b$ of already available\footnotetext[3]{Bermudez, Bailleux, and Cernicharo, {\em A\&A}~{\bf 598} (2017) A9}\footnotetext[4]{Chitarra, Martin-Drumel, Gans, Loison, Spezzano, Lattanzi, M\"uller, and Pirali, {\em A\&A}~{\bf 644} (2020) A123}$^{c,d}$ and newly measured sub-millimeter wave spectroscopic data will be reported. The fitted value of the tunneling splitting will be compared to that retrieved from the torsional energy level calculation. The rotational dependence of the tunneling splitting will be discussed. Issue Date: 2021-06-25 Publisher: International Symposium on Molecular Spectroscopy Genre: Conference Paper / Presentation Type: Text Language: English URI: http://hdl.handle.net/2142/111223 Date Available in IDEALS: 2021-09-24
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