Internal rotation in the spectrum of acetaldehyde

Abstract

The geometrical structure of acetaldehyde from the microwave spectrum and torsional transitions from the far infrared spectrum have been fitted with a semirigid model in order to obtain the torsional parameters V″ 3 = 415.0 and V″ 6 = 22.3 cm −1 and the torsional energy levels of the isotopic species CH 3CHO, CH 3CDO, CD 3CHO, and CD 3CDO. These have been used in fitting torsional sequences in the 182-nm system of the electronic spectra of these species to obtain the excited state parameters V′ 3 = 880 and V′ 6 = 77 cm −1. Both the ground and excited state parameters are in good agreement with ab initio predictions.