Theoretical Spectroscopic Study of Two Ketones of Atmospheric Interest: Methyl Glyoxal (CH₃COCHO) and Methyl Vinyl Ketone (CH₃COCH═CH₂)

Abstract

Two ketones of atmospheric interest, methyl glyoxal and methyl vinyl ketone, are studied using explicitly correlated coupled cluster theory and core–valence correlation-consistent 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 (V 3 = 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.

Theoretical Spectroscopic Study of Isopropyl Alcohol (CH3-CHOH-CH3)

“…Table 2 collects the ground vibrational state rotational parameters computed using a multipart approach summarized in Equation (1). This equation has been proposed and verified in previous studies (Toumi et al 2022). The basis is that the most contributed term is determined using a very expensive computational tool.…”

“…The rotational constants were computed using the CCSD(T)-F12 equilibrium parameters, A e , B e , and C e , and the MP2/ AVTZ vibrational contribution to the rotational constants, ΔB vib , computed from the VPT2 α ir vibration-rotation interaction parameters. The following equation, proposed and verified in previous studies (Toumi et al 2022), summarizes the procedure:…”

Theoretical structural and spectroscopic characterization of peroxyacetic acid (CH3–CO–OOH): study of the far infrared region

“…The vibrational ground state rotational constants reported in Table 3 were calculated from the CCSD(T)-F12b equilibrium rotational constants using the following equation: B 0 = B e (CCSD(T)-F12b/CVTZ-F12) + Δ B vib (MP2)/AVTZpreviously tested for another molecules. 34,35 Here, Δ B vib represents the vibrational contribution derived from the MP2/AVTZ cubic force field. The vibrational second-order perturbation theory was used to calculate the α i r vibration–rotation interaction parameters.…”

“…Divergences coincide with previous studies of other molecules such as methyl glyoxal or methyl vinyl ketone, performed at the same level of theory. 34…”

Energetics of the OH radical H-abstraction reactions from simple aldehydes and their geminal diol forms

“…Substitution of one of the hydrogen atoms by a methyl group, as in acetaldehyde, diminishes markedly the preference towards the diol species, but it is kept if the C is another carbonyl like in -oxo aldehydes. In this context, glyoxal [9,10,15] and methylglyoxal [10,12,[13][14][15][16][17][18][19][20][21] have been frequently studied in recent years.…”