Fully Atomistic Real-Time Simulations of Transient Absorption Spectroscopy.

We have implemented an electron-nuclear real-time propagation scheme for the calculation of transient absorption spectra. When this technique is applied to the study of ultrafast dynamics of Soret-excited zinc(II) tetraphenylporphyrin in the subpicosecond time scale, quantum beats in the transient absorption caused by impulsively excited molecular vibrations are observed. The launching mechanism of such vibrations can be regarded as a displacive excitation of the zinc-pyrrole and pyrrole C-C bonds.