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

Abstract

Torsional and rotational spectroscopic properties of pyruvic acid are determined using highly correlated ab initio methods and combining two different theoretical approaches: Second order perturbation theory and a variational procedure in three-dimensions. Four equilibrium geometries of pyruvic acid, Tc, Tt, Ct, and CC, outcome from a search with CCSD(T)-F12. All of them can be classified in the Cs point group. The variational calculations are performed considering the three internal rotation modes responsible for the non-rigidity as independent coordinates. More than 50 torsional energy levels (including torsional subcomponents) are localized in the 406–986 cm−1 region and represent excitations of the ν24 (skeletal torsion) and the ν23 (methyl torsion) modes. The third independent variable, the OH torsion, interacts strongly with ν23. The A1/E splitting of the ground vibrational state has been evaluated to be 0.024 cm−1 as it was expected given the high of the methyl torsional barrier (338 cm−1). A very good agreement with respect to previous experimental data concerning fundamental frequencies (νCAL − νEXP ~ 1 cm−1), and rotational parameters (B0CAL − B0EXP < 5 MHz), is obtained.

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

“…In previous studies, we determined the parameters discriminating valence and core electrons. Correlation effects due to the valence electrons were evaluated at the CCSD­(T)-F12 level of theory, while CCSD­(T) theory was used to describe the core correlation effects. − ,, Generally, the approximation led to an error in one of the constants larger than for the other two parameters. In the present case, both correlation effects were treated together using CCSD­(T)-F12 and a suitable basis set.…”

“…The present study is based on highly correlated ab initio calculations. The goal is to provide structural and spectroscopic theoretical data with an emphasis on the FIR region following the same procedure employed for the interconnecting carbonyl species pyruvic acid and acetone. − We study both molecules in the same paper because they share properties. Both species can be considered as acetone derivatives in which one acetone methyl group has been substituted by another functional group, −CHO or −CHCH 2 .…”

Probing the dynamics of the photo-induced decarboxylation of neutral and ionic pyruvic acid

“…For the methyl internal rotation, potential barriers of 0.042 eV, 0.049 eV, 0.067 eV and 0.106 eV were determined for Tc, Tt, Ct and Cc, respectively. 10,22 These barriers are relatively high to allow these conversions given the actual experimental conditions. Indeed, at present, gas phase PA molecules are seeded in a cooled molecular beam, with translational temperatures of T ∼ 110 K, as extracted from the KERD of the parent molecule (see Fig.…”

“…10–19 These works are complemented by theoretical computations at the density functional theory (DFT) and post Hartree–Fock configuration interaction levels. 16,19–26…”

“…[10][11][12][13][14][15][16][17][18][19] These works are complemented by theoretical computations at the density functional theory (DFT) and post Hartree-Fock conguration interaction levels. 16,[19][20][21][22][23][24][25][26] The electronic structure of PA is known through the analysis of its UV-vis spectrum and theoretical computations. [27][28][29][30] These works located the adiabatic energy for the S 0 -S 1 transition at 3.31 eV and the vertical excitation energies of the S 0 -S 2 and the S 0 -S 3 transitions at 5.60 eV and 7.00 eV, respectively.…”