One- and two-dimensional models of torsional and inversion vibrations in 2-chloroethanal in the lowest triplet excited state

Ab initio quantum-mechanical calculations of the structure of the conformat ionally nonrigid 2-chloroethanal (CE, CClH2CHO) molecule in the lowest exci ted tripler (T-1) state were performed. Electronic excitation of the trans and cis CE conformers from the ground (S-0) to the T-1 electronic state was found to cause substantial changes in their structure; in particular, the CClH2 tops turned, and the CCHO fragments became nonplanar. Six minima of t he potential energy surface of CE in the T-1 state corresponded to three pa irs of mirror-symmetrical conformers. The calculated nb initio potential en ergy surface of CE in the T-1 state was used to solve the problem of torsio nal and inversion motions of nuclei in the one-dimensional approximation an d the two-dimensional torsional-inversion problem. Torsional and inversion motions were found to be interrelated.