The rotational spectrum of methanol in the third excited torsional stateThis article is part of a Special Issue on Spectroscopy at the University of New Brunswick in honour of Colan Linton and Ron Lees.We dedicate this paper to Dr. R.M. Lees, one of the early pioneers of methanol spectroscopy and internal rotation theory. Indeed, inspired by his 1968 methanol paper (Lees and Baker. J. Chem. Phys. 48, 5299 (1968)), numerous methanol studies have been matured and brought to the next level of ever chal

Abstract

The rotational spectrum of methanol in its third excited torsional state, v t = 3, as well as the K = 0 A-state of v t = 4, has been recorded and analyzed in the 8-1654 GHz frequency range. The v t = 3 state lies well above the top of the torsional barrier and the majority of the energy origins for the various K sub-bands lie below the C-O stretching fundamental vibration. Only the a-type R-branch spectrum was observed in this frequency range, suggesting that the near torsional degeneracy required for a b-type spectrum in the microwave accidentally reduces the torsional overlap, making these transitions very weak. The A-state K = 4 of vt = 3 interaction with the C-O stretch torsional ground state K = 0 + and K = 1 + has been accounted for. The E-state K = -5 level could be fit directly with a power series in spite of its resonance with the C-O stretch torsional ground state K = -5 level. The a R-branch of the K = 0 A-state vt = 4 sub-band is also provided and the origin of this band resonance with the C-O stretch is discussed. The data have been modeled with a power series to near experimental accuracy. The measured and calculated spectrum should facilitate radio astronomical assignments of vt = 3 transitions in hot sources.PACS Nos: 33.15.Mt, 33.20.Vq Résumé : Nous avons enregistré et analysé dans le domaine de 8 à 1654 GHz le spectre de rotation du méthanol dans son troisième état de torsion, v t = 3, ainsi que l'état A, K = 0 de v t = 4. L'état v t = 3 est loin au dessus du maximum de la barrière de torsion et la plus grande partie de l'énergie pour les différentes sous-bandes K se trouve sous l'énergie de la vibration fondamentale d'étirement C-O. Seule la branche R de type-a a été observée dans ce domaine, suggérant que la quasi dégénérescence en torsion, requise par le spectre de type b dans les micro-ondes, réduit accidentellement le recouvrement en torsion, rendant ces transitions très faibles. Nous avons tenu compte de l'interaction entre l'état A, K = 4 de v t = 3 avec l'état d'étirement C-O K = 0 + (fondamental) et K = 1 + . L'état E K = -5 trouve directement sa place dans la série de puissance, malgré sa résonance avec le niveau fondamental de torsion C-O K = -5. La branche a R de l'état A K = 0 de la sous-bande v t = 4 trouve aussi sa place et nous analysons l'origine de sa résonance avec l'étirement C-O. Les données ont été modélisées par une série de puissance à une précision approchant la précision expérimentale. Les spectres mesurés et modélisés devraient faciliter l'attribution des transitions vt = 3 dans les sources chaudes en astrophysique.[Traduit par la Rédaction]

Sub-Doppler infrared spectroscopy of CH2OH radical in a slit supersonic jet: Vibration-rotation-tunneling dynamics in the symmetric CH stretch manifold

“…Indeed, while methanol is also an extremely important interstellar oxygen-containing molecule, it exhibits such a congested spectrum that it has been referred to as an interstellar "weed." [22][23][24][25][26] As a result, positive identification of the hydroxymethyl radical in the interstellar medium will require highest quality predictions from precise ground vibrational state constants, the determination of which is a primary goal of this work.…”