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

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