On-the-fly simulations of transient absorption pump-probe spectra: combining mapping dynamics with doorway-window protocol

We have developed an ab initio protocol for the simulation of transient-absorption (TA) pump-probe (PP) signals of realistic polyatomic systems. The protocol is based on interfacing the doorway-window representation of spectroscopic signals with the on-the-fly mapping Hamiltonian dynamics approach at the symmetrical quasi-classical/Meyer-Miller (SQC/MM) level. The methodology is applied to the simulation TA PP signals of two molecular systems, azobenzene and cis-hepta-3,5,7-trieniminium cation (PSB4). For both molecules, the TA PP spectra were demonstrated to give a direct fingerprint of the excited state wavepacket dynamics and internal conversion, as well as permit the monitoring of the isomerization pathways en route to the final photoproducts.