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 structure of the conformationally nonrigid chloral (CCl₃CHO) molecule in the ground (S₀) and lowest excited triplet (T₁) states. Electronic excitation causes substantial changes in molecular geometry: the CCl₃ top is rotated, and the carbonyl (CCHO) fragment becomes nonplanar. For the torsional (S₀ and T₁) and inversion (T₁) nuclear vibrations, one- (S₀ and T₁) and two-dimensional (T₁) vibrational problems are solved; a relationship is found between the torsional and inversion vibrations in the T₁ state. The results are compared with the data of analogous calculations for the acetaldehyde molecule in the T₁ state.