Reinvestigation of the rotation-tunneling spectrum of the CH2OH radical

Context. The hydroxymethyl radical (CH2OH) is one of two structural isomers, together with the methoxy radical (CH3O), that can be produced by abstraction of a hydrogen atom from methanol (CH3OH). In the interstellar medium (ISM), both CH2OH and CH3O are suspected to be intermediate species in many chemical reactions, including those of formation and destruction of methanol. The determination of the CH3O/CH2OH ratio in the ISM would bring important information concerning the formation processes of these species in the gas and solid phases. Interestingly, only CH3O has been detected in the ISM so far, despite the recent first laboratory measurement of the CH2OH rotation-tunneling spectrum. This lack of detection is possibly due to the non-observation in the laboratory of the most intense rotation-tunneling transitions at low temperatures. Aims. To support further searches for the hydroxymethyl radical in space, we present a thorough spectroscopic study of its rotation-tunneling spectrum, with a particular focus on transitions involving the lowest quantum numbers of the species. Methods. We recorded the rotation-tunneling spectrum of CH2OH at room temperature in the millimeter-wave domain using a frequency multiplication chain spectrometer. A fluorine-induced H-abstraction method from methanol was used to produce the radical. Results. About 180 transitions were observed, including those involving the lowest N and Ka quantum numbers, which are predicted to be intense under cold astrophysical conditions. These transitions were fitted together with available millimeter-wave lines from the literature. A systematic observation of all components of the rotational transitions yields a large improvement of the spectroscopic parameters allowing confident searches of the hydroxymethyl radical in cold to warm environments of the ISM.

Synthesis of Fluorescent Dansyl Derivatives of Methoxyamine and Diphenylhydrazine as Free Radical Precursors

Starting from dansyl-chloride, in reaction with 1,1-diphenylhydrazine and methoxyamine, two new fluorescent derivatives 1 and 2 were obtained and characterized by NMR, IR, UV-Vis, HR-MS, and fluorescence spectroscopy. The single-crystal X-ray structure was obtained for compound 2. Both compounds generate free radicals by oxidation, as demonstrated by ESR spectroscopy. Compound 1 generates the corresponding hydrazyl-persistent free radical, evidenced directly by ESR spectroscopy, while compound 2 generates in the first instance the methoxyaminyl short-lived free radical, which decomposes rapidly with the formation of the methoxy radical, evidenced by the ESR spin-trapping technique. By oxidation of compounds 1 and 2, their fluorescence is quenched.

Hydrogen transfer reaction: Bond formation and bond cleavage through the eyes of interacting quantum atoms

Hydrogen transfer from hydroquinone to the methoxy radical was studied using the density functional theory. The energy decomposition technique, interacting quantum atoms, was employed for a detailed investigation of the changes that the bonds of interest go through along the minimum energy path in the vicinity of the transition state. The whole system was divided either into two or three fragments. The two-fragment analysis enabled investigation of the bond that is formed or the one that is cleaved by defining the fragments as reactants and as products, respectively. The three-fragment analysis (the fragments being semiquinone, hydrogen atom and methoxy radical) was used for the simultaneous analysis of the two phenomena, bond cleavage and bond formation. Additionally, it enabled the interaction between the particle that donates the hydrogen atom and the one that accepts it to be investigated. This interaction is characterized by attractive non-classical and repulsive classical interactions. It was demonstrated that the transferring hydrogen atom undergoes the most pronounced energy changes and gives the largest contribution to the deformation energy.

Comment on “Isomerization of the methoxy radical revisited: the impact of water dimers” by B. Bandyopadhyay et al., Phys. Chem. Chem. Phys., 2016, 18, 27728 and “Isomerization of methoxy radical in the troposphere: competition between acidic, neutral and basic catalysts” by P. Kumar, B. Bandyopadhyay et al., Phys. Chem. Chem. Phys., 2017, 19, 278

Isomerization would be unimportant even if it was not slow.

Correction: Comment on “Isomerization of the methoxy radical revisited: the impact of water dimers” by B. Bandyopadhyay et al., Phys. Chem. Chem. Phys., 2016, 18, 27728 and “Isomerization of methoxy radical in the troposphere: competition between acidic, neutral and basic catalysts” by P. Kumar, B. Bandyopadhyay et al., Phys. Chem. Chem. Phys., 2017, 19, 278

Correction for ‘Comment on “Isomerization of the methoxy radical revisited: the impact of water dimers” by B. Bandyopadhyay et al., Phys. Chem. Chem. Phys., 2016, 18, 27728 and “Isomerization of methoxy radical in the troposphere: competition between acidic, neutral and basic catalysts” by P. Kumar, B. Bandyopadhyay et al., Phys. Chem. Chem. Phys., 2017, 19, 278’ by Theodore S. Dibble et al., Phys. Chem. Chem. Phys., 2018, 20, 11481–11482.