Theoretical study of the structure of propanal in the first excited singlet and triplet electronic states: three-dimensional model for torsional and inversion vibrations

Abstract

Potential energy surfaces of the conformationally nonrigid propanal molecule (CH 3CH 2CHO) in the lowest excited triplet (T 1) and singlet (S 1) electronic states were calculated by the multiconfigurational self-consistent field method CASSCF. Electronic excitations of the propanal conformers from the ground state (S 0) to the excited states (T 1 and S 1) were demonstrated to cause essential changes in the molecular structure, viz. the rotation of the ethyl tops and the out-of-plane distortion of carbonyl fragments. Nuclear vibrational motions in the propanal molecule in the excited electronic states were analyzed both in the harmonic approximation and by the use of the one-, two-, and three-dimensional variational calculations to describe correlated large-amplitude vibrations.