Theoretical Spectrscopic Study of Two Ketones of Atmospheric Interest: Methyl Glyoxal (CH3COCHO) and Methyl Vinyl Ketone (CH3COCH=CH2) Toumi, Insaf Carvajal Rodríguez, Miguel Ángel Two ketones of atmospheric interest, methyl glyoxal and methyl vinyl ketone, are studied using explicitly correlated coupled cluster theory and core−valence correlationconsistent basis sets. The work focuses on the far-infrared region. At the employed level of theory, the rotational constants can be determined to within a few megahertz of the experimental data. Both molecules present two conformers, trans/cis and antiperiplanar (Ap)/ synperiplanar (Sp), respectively. trans-Methyl glyoxal and Ap-methyl vinyl ketone are the preferred structures. cis-Methyl glyoxal is a secondary minimum of very low stability, which justifies the unavailability of experimental data in this form. In methyl vinyl ketone, the two conformers are almost isoenergetic, but the interconversion implies a relatively high torsional barrier of 1798 cm−1. A very low methyl torsional barrier was estimated for trans-methyl glyoxal (V3 = 273.6 cm−1). Barriers of 429.6 and 380.7 cm−1 were computed for Ap- and Sp-methyl vinyl ketone. Vibrational second-order perturbation theory was applied to determine the rovibrational parameters. The far-infrared region was explored using a variational procedure of reduced dimensionality. For trans-methyl glyoxal, the ground vibrational state was estimated to split by 0.067 cm−1, and the two low excited energy levels (1 0) and (0 1) were found to lie at 89.588 cm−1/88.683 cm−1 (A2/E) and 124.636 cm−1/123.785 cm−1 (A2/E). For Ap- and Sp-methyl vinyl ketone, the ground vibrational state splittings were estimated to be 0.008 and 0.017 cm−1, respectively. 2022-11-09T09:45:40Z 2022-11-09T09:45:40Z 2022-09-30 journal article J. Phys. Chem. A 2022, 126, 7230−7241. [https://doi.org/10.1021/acs.jpca.2c05653] https://hdl.handle.net/10481/77843 10.1021/acs.jpca.2c05653 eng info:eu-repo/grantAgreement/EC/H2020/872081 http://creativecommons.org/licenses/by/4.0/ open access Atribución 4.0 Internacional American Chemical Society