Theoretical Chemistry and Physics Department Institute for the Structure of Matter IEM-CSIC, Serrano 121, 28006 Madrid, Spain.
Laboratory of Applied Chemistry and Environment, Department of Chemistry, Faculty of Science, Ibn Zohr University, Agadir B.P. 8106, Morocco.
Molecules. 2021 Jul 14;26(14):4269. doi: 10.3390/molecules26144269.
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 C 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 region and represent excitations of the ν (skeletal torsion) and the ν (methyl torsion) modes. The third independent variable, the OH torsion, interacts strongly with ν. The A/E splitting of the ground vibrational state has been evaluated to be 0.024 cm as it was expected given the high of the methyl torsional barrier (338 cm). A very good agreement with respect to previous experimental data concerning fundamental frequencies (ν - ν ~ 1 cm), and rotational parameters (B - B < 5 MHz), is obtained.
二级微扰理论和三维变分程序，确定了丙酮酸的扭转和旋转光谱性质。通过 CCSD(T)-F12 搜索得到了丙酮酸的四种平衡几何结构 Tc、Tt、Ct 和 CC，它们都可以归类为 C 点群。变分计算考虑了负责非刚性的三个内部旋转模式，将它们作为独立坐标进行计算。超过 50 个扭转能级（包括扭转子分量）定位于 406-986cm 区域，代表 ν（骨架扭转）和 ν（甲基扭转）模式的激发。第三个独立变量，OH 扭转，与 ν 强烈相互作用。由于甲基扭转势垒较高（338cm），预计基态振动能级的 A/E 劈裂为 0.024cm，这与实验数据在基本频率（ν-ν~1cm）和旋转参数（B-B<5MHz）方面非常吻合。
