ABSTRACT
The geometrical structure, conformer energy differences, and conformational and vibrational dynamics of acrolein in (1,3)(pi,pi(*)) electronic states were investigated using a number of single- and multi-reference quantum-chemical methods. Peculiarities of acrolein in the (1)(pi,pi(*)) state were described with both conformers being significantly non-planar. A Valence Focal-Point Analysis of the conformer energy difference in the (3)(pi,pi(*)) state was performed. The coupling of the internal rotation about C-C and C=C bonds with large amplitude molecular motions, such as non-planar distortions of carbonyl, methylene, and methyne fragments was also investigated. The corresponding two-dimensional PES sections were constructed.
Subject(s)
Acrolein/chemistry , Quantum Theory , Models, Molecular , Molecular ConformationABSTRACT
The structure of the conformationally flexible acetyl fluoride molecule (CH3CFO and CD3CFO) in the ground (S0) and lowest excited triplet (T1) and singlet (S1) electronic states was calculated by different quantum-chemical methods (RHF, UHF, MP2, CASSCF). The equilibrium geometric parameters and harmonic vibrational frequencies of the molecules in these electronic states were estimated. The calculations demonstrated that the electronic excitation causes considerable conformational changes involving the rotation of the CH3(CD3) top and a substantial deviation of the CCFO carbonyl fragment from planarity. For large-amplitude vibrations, namely, for the torsional vibration in the S0 state and the torsional and inversion (nonplanar carbonyl fragment) vibrations in the T1 and S1 states, the quantum-mechanical problems were solved in one-dimensional (1D) and two-dimensional (2D) approximations. The results of calculations are in good agreement with experimental data.
