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 struct ure of 2,2-dichloroethanal (I)CE, CHCl2CHO) in the ground (S-0) and excited lowest triplet (T-1) states. It is found that electronic excitation of DCE from the S-0 to T-1 state occurs with top rotations and a loss of planarit y of the carbonyl fragments. Six minima corresponding to three pairs of ena ntiomers were found on the potential energy surface (PES) of the DCE molecu le in the T-1 state. Based on the PES calculated (by the UHF and CASSCF met hods in a 6-31G** basis) for DCE in the T-1 state, the one-dimensional tors ional and inversion problems and the two-dimensional torsional-inversion pr oblems are solved. A comparison of the results has revealed a relationship bem,een the torsional and inversion inotions.