The Formation of C₃O₃H₆ Structural Isomers in the Gas Phase through Barrierless Pathways: Formation and Spectroscopic Characterization of Methoxy Acetic Acid

Abstract

Gas phase formation processes feasible at low temperatures are determined theoretically for 38 isomers obeying the C3O3H6 empirical formula, one of them, the simplest ketose dihydroxyacetone, has been observed in gas phase sources. A preliminary search for isomeric forms first targets ethoxy formic acid (C2H5–O–COOH) as the most stable isomer followed by lactic acid. Profiles corresponding to the minimum energy pathways reveal that the favored conformers of 14 of these isomers can be formed in the gas phase through 29 barrierless processes involving the OH*, CH3O*, HCO*, CH3*, CH2OH, HCOO*, and OHCO* radicals, all of them observed in the interstellar medium. Kinetic rates are provided at 200, 298, and 500 K, confirming the suitability of 16 processes at low temperatures. Faster processes involve the OH hydroxyl radical whereas, to a lesser degree, the processes involving the HOCO radical and the methoxy methyl radical CH3O*, are quite significant. Spectroscopic parameters (rovibrational and torsional) are obtained for methoxy acetic acid (CH3–O–CH2COOH) for which two low-lying isoenergetic conformers can be produced from the CH3OCH2* radical predicted to be a precursor of abundant observed molecules. Profiles and spectroscopic properties make methoxy acetic acid a good candidate to be detected in the gas phase of extraterrestrial sources.

Large Amplitude Motions of Pyruvic Acid (CH3-CO-COOH)

“…Since the classification of the resulting levels is really difficult given the large density of states in the same region, procedures developed for previous studies were employed for a right assignment. The properties of the 3D-wavefunctions and the contribution of the contracted basis functions [27,42] allow assigning the main part of the energies. The assignments of few E components (in blue in Table 6) are not conclusive.…”

“…The symmetry adapted triple Fourier series were employed as trial functions. To reduce dimensionality, a contracted basis set was employed for the C-C torsional coordinate performing a pre-diagonalization of the Hamiltonian matrix [27,42]. This route helps the classification of the resulting energies.…”

Theoretical spectroscopic study of acetyl (CH3CO), vinoxy (CH2CHO), and 1-methylvinoxy (CH3COCH2) radicals. Barrierless formation processes of acetone in the gas phase

“…It is generally accepted that organic compounds are formed in the interstellar medium on ice mantles, although the possibility of gas phase processes is not ignored 10 . At the temperatures and pressures of the interstellar medium, barrierless processes can be competitive with respect to those involving ice mantles 11 . Barrierless processes involve low stability species such as radicals, charged or unsaturated molecules 11 .…”

“…At the temperatures and pressures of the interstellar medium, barrierless processes can be competitive with respect to those involving ice mantles 11 . Barrierless processes involve low stability species such as radicals, charged or unsaturated molecules 11 .…”

“…Following the same methodology employed in a previous work 11 , for this paper, gas phase barrierless processes and the corresponding kinetic rates were studied at different temperatures. Probable exergonic bimolecular addition processes, the reactants which are acetone fragments or small neutral species observed in the gas phase sources containing C, O and H atoms, are described.…”