<i>Ab initio</i> study of the far infrared spectrum and gas phase formation reactions of methyl ethyl ketone (CH3–CO–CH2–CH3)

Abstract

Highly correlated ab initio calculations are employed for a complete spectroscopic characterization of methyl ethyl ketone (MEK). Thermochemical and kinetic properties of formation processes, suitable for the gas phase atmospheric and astrophysical environments, are determined. Among 13 formation processes, three bi-radical addition reactions were found as the most likely, for which the temperature-dependent rate coefficients are provided. The search of conformers at the CCSD(T)-F12 level of theory leads to two stable structures Ap (Cs) and Sp (C1), which depend strongly on the correlation energy. The stability of Ap-MEK is noticeable, whereas Sp can transform into Ap by vibrational excitations at very low temperatures since conformers are separated by low energy barriers. Three internal rotations, the torsion of ethyl group (α), and the torsions of the two methyl groups (θac and θet) interconvert 27 minima of the potential energy surface. In both conformers, V3ac <<< V3et. To explore the far infrared region and to map the low torsional energy levels and splittings, a variational procedure of reduced dimensionality is employed. The ground vibrational state splits into nine components distributed in two groups at 0.0 cm-1 (A1 and E2) and 0.289 cm-1 (E1, E3, and E4). Accurate rotational parameters are provided.