Excited state dynamics of the s-trans-1, 3-butadiene cation: An ab initio quantum dynamical analysis.

The excited state dynamics of the s-trans-1,3-butadiene cation, focusing on the second and third bands of the photoelectron spectrum, have been investigated using a fully quantal approach, for the first time. The five lowest electronic states XB, AA, BA, CB, and DA considering the six vibrational modes S, S, S, S, S, and S were taken into account in the nuclear quantum dynamical investigation. The potential energy curves have been calculated along these coordinates for the five lowest electronic states using the RS2C method. Our simulations indicate a moderately fast population transfer from the AA and BA to the XB state, taking place on a time scale of 70-80 fs. Furthermore, the computed second and third bands of the photoelectron spectrum are in good agreement with the corresponding experimental ones. Our calculation identifies the symmetric stretching of the central C-C bond S and the symmetric C-C-C bending S to be the main progression modes of the second and third bands of the photoelectron spectrum of (cationic) s-trans-1,3-butadiene.