On-the-Fly Trajectory Simulation of Two-Pulse, Three-Pulse, and Higher-Order Pump–Probe Signals

We have developed a protocol for the on-the-fly simulation of 2-pulse, 3-pulse, and general K -pulse pump–probe (PP) signals by semiclassical trajectory methods. The protocol employs the doorway-window approximation, which implies temporally well-separated pulses. The methodology is based on a nontrivial generalization of the approach by Gelin et al. ( J. Chem. Theory Comput. 2021, 17, 2394), originally developed for the evaluation of conventional 2-pulse PP signals. The protocol requires only electronic transition dipole moments and electronic energies along the semiclassical trajectories as input parameters. The explicit, ready-to-use expressions for the evaluation of 3-pulse PP signals are derived and discussed in detail.