Competitive Gas Phase Reactions for the Production of Isomers C₂O₂H₄. Spectroscopic Constants of Methyl Formate

Abstract

New routes for the chemical formation of the C2O2H4 isomers in the gas phase are explored searching for a justification of the prominent astrophysical abundance of methyl formate with respect to the most stable one acetic acid. Kinetic rate constants at low temperatures are provided for eight barrierless reaction pathways. In addition, the spectroscopic parameters are computed using highly correlated ab initio methods for the main isotopologue of methyl formate and for five monosubstituted isotopologues containing 13C, 18O, and deuterium. Accurate rotational constants are obtained at the CCSD­(T)-F12 level of theory. The dipole moments components are provided. Centrifugal distortion constants, rovibrational parameters, and Fermi displacements are predicted using second order perturbation theory. A variational procedure of reduced dimensionality is applied to determine band center positions for transitions corresponding to the large amplitude motions. The COC bending mode is considered explicitly as an independent coordinate to evaluate its resonances with the torsional energies. The effect of resonances is proven as negligible.

Rotational and Torsional Properties of Various Monosubstituted Isotopologues of Acetone (CH3–CO–CH3) from Explicitly Correlated Ab Initio Methods

“…For other isotopologues, the far-infrared spectrum has not been explored and accurate calculations of the torsional energies, are no available. In previous papers devoted to methyl formate and dimethyl-ether, both species were studied using ab initio calculations and new experiments. − The ab initio calculations were accurate enough to confirm earlier assignments and to underline very small inaccuracies in those previous assignments for one of the torsional overtones. Consequently, the far-infrared region was revisited performing new measurements at different temperatures and new assignments basis on the theoretical predictions.…”

“…In the present paper, as we did in the previous papers for the other species, − ab initio calculations are employed to determine spectroscopic parameters (rotational and centrifugal distortion constants and low vibrational energy levels which can be populated at low temperatures) of various acetone monosubstituted isotopes. Ab initio parameters can confirm or refute previous assignments, can be used as initial data in assignments using effective Hamiltonians, and can require new inquires.…”

Vibrational study of hydrated methyl formate complexes in solid neon: Observation for the first time of three isomers for methyl formate-water complex

“…Concerning the MF monomer geometry, two stable structures have been calculated [5,6], a syn one, the most stable, and an anti one with a difference of relative energy of 5.3 kcal/mol. A recent study at correlated coupled cluster calculations (CCSD(T)-F12) level [7] shows an anti -syn barrier of 4616 cm -1 (13.2 kcal/mol) with a difference of stability of 1730 cm -1 (4.95 kcal/mol). The fundamental frequencies have been calculated for the both structures and compared with previous gas phase infrared data of MF only for the syn observed structure [8][9][10].…”

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

“…In a previous work, we attended the spectroscopy and the formation of C 2 O 2 H 4 isomers starting by 62 reactants (Senent 2001a(Senent , 2004Senent et al 2005;Gámez et al 2019a). With this new paper, devoted to the C 3 O 3 H 6 family, we want to take a step forward in complexity by taking care of larger species.…”