Structure and Conformational Dynamics of a 2,2-Dimethylpropanal Molecule in the Lowest Excited Singlet (S1) and Triplet (Т1) Electronic States

The geometric structure, PES, and conformational dynamics of a 2,2-dimethylpropanal molecule in the lowest excited singlet and triplet electronic states are studied using the multiconfigurational CASPT2/def2-TZVPP approach. The problem of large-amplitude nuclear motions (the rotation of the tert -butyl group and the inversion of the nonplanar carbonyl moiety) is solved for each electronic state by variational means. It is shown that electronic excitation to both states causes the pyramidalization of the ССHO carbonyl moiety and rotation of the tert -butyl group. Results confirm the qualitative conclusions of an earlier analysis of the S 1 ← S 0 vibronic spectrum of a 2,2-dimethylpropanal molecule.