Ab initio strong-pump strong-probe doorway-window simulation protocol

Area of Science:

• Chemical Physics
• Computational Chemistry
• Spectroscopy

Background:

• Pump-probe (PP) spectroscopy is a powerful technique for studying molecular dynamics.
• Simulating strong-field PP spectra is computationally demanding.
• Existing methods are often limited to weak-field approximations.

Purpose of the Study:

• To develop an efficient and accurate methodology for simulating strong-field pump-probe spectra.
• To generalize the semiclassical doorway-window (DW) protocol to arbitrary pulse intensities.
• To investigate the impact of strong fields on spectral information content.

Main Methods:

• Developed an on-the-fly semiclassical trajectory methodology.
• Defined strong-field doorway-window (DW) functions using analytical formulas.
• Evaluated molecular transition dipole moments and electronic energies along semiclassical trajectories.
• Applied the method to simulate strong-field PP spectra of pyrazine.

Main Results:

• The methodology allows simulation of strong-field PP spectra at comparable computational cost to weak-field simulations.
• Strong pump and probe pulses significantly increase the information content of PP measurements.
• A strong probe pulse enhances weak transitions from low-lying excited states.
• Nonadiabatic wavepacket dynamics in weakly allowed states of pyrazine become visible.

Conclusions:

• The developed methodology provides an efficient way to simulate strong-field PP spectra.
• Strong-field spectroscopy offers enhanced insights into molecular dynamics, particularly for weakly allowed transitions.
• This approach can reveal complex wavepacket dynamics previously obscured in weak-field experiments.