Ab initio Quantum-Mechanical Calculations of Molecular Structure and Conformations of 2,2-Dichloroethanal in the Ground and Excited Lowest Triplet States

Ab initio calculations were carried out to investigate the molecular structure of 2,2-dichloroethanal (DCE, CHCl2CHO) in the ground (S0) and excited lowest triplet (1) states. It is found that electronic excitation of DCE from the S0 to T1 state occurs with top rotations and a loss of planarity of the carbonyl fragments. Six minima corresponding to three pairs of enantiomers were found on the potential energy surface (PES) of the DCE molecule in the 1 state. Based on the PES calculated (by the UHF and CASSCF methods in a 6-31G** basis) for DCE in the 1 state, the one-dimensional torsional and inversion problems and the two-dimensional torsional-inversion problems are solved. A comparison of the results has revealed a relationship between the torsional and inversion motions.