Theoretical characterization of hydroxyacetone (CH-CO-CHOH) in the gas phase. Study of the far infrared region.

Accurate structural and rovibrational parameters of hydroxyacetone, CH-CO-CHOH, are computed using highly correlated ab initio methods (CCSD(T)-F12), second order perturbation theory, and a variational procedure of reduced dimensionality, contemplating the interconversion of the conformers by internal rotation at low temperatures. Hydroxyacetone presents four different stable geometries. The preferred one, whose stability is prominent, is a quasi-planar structure slightly distorted due to the formation of an intramolecular hydrogen bond involving the OH hydrogen and the C=O oxygen atom. Rotational constants are computed to be A = 10092.77 MHz, B = 3808.75 MHz and C = 2863.19 MHz at less than 1 MHz from the experimental parameters confirming the non-planarity of the preferred conformer. Low-lying vibrational energy levels up to 500 cm are determined variationally obtaining an A/E splitting of 5.227 cm for the ground vibrational state. The fundamentals ν (C-CHOH torsion) and ν (OH torsion) are found at 146.638 cm (A) and 129.583 cm (E), and 349.147 cm (A) and 353.661 cm (E), respectively. For the most stable conformer, a complex band structure of the far infrared spectrum due to the effects of the low methyl torsional barrier (V = 72 cm) and the non-planarity, is predicted. The subcomponents of the methyl torsion fundamental (ν) are found at 54.566 cm (A → A) and 81.243 cm (E → E).