Molecular structure and conformations of chloral (CCl3CHO) in the ground and lowest triplet states

This paper reports on an ab initio quantum mechanical calculation of the st ructure of the conformationally nonrigid chloral (CCl3CHO) molecule in the ground (SO) and lowest excited triplet (T-1) states. Electronic excitation causes substantial changes in molecular geometry: the CCl3 top is rotated, and the carbonyl (CCHO) fragment becomes nonplanar. For the torsional (So a nd T-1) and inversion (T-1) nuclear vibrations, one- (S-0 and T-1) and two- dimensional (T-1) vibrational problems are solved; a relationship is found between the torsional and inversion vibrations in the T-1 state. The result s are compared with the data of analogous calculationsfor the acetaldehyde molecule in the T-1 state.