Quasiclassical Doorway-Window Simulation of Femtosecond Transient-Absorption Pump-Probe Signals Beyond the Weak-Pump...

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Spectroscopy

Background:

• Transient absorption spectroscopy is crucial for studying ultrafast molecular dynamics.
• Simulating strong-pump signals traditionally requires significant computational resources.
• Previous methods like weak-pulse approximations have limitations in capturing intense field effects.

Purpose of the Study:

• To develop an efficient ab initio on-the-fly protocol for simulating strong-pump transient absorption (TA) signals.
• To enable accurate TA signal evaluation at a computational cost comparable to weak-pulse methods.
• To investigate the influence of pump pulse intensity on TA spectral features.

Main Methods:

• Combined trajectory surface hopping with the classical doorway-window approximation.
• Developed an *ab initio* on-the-fly simulation protocol.
• Applied the method to simulate pyrazine's strong-pump TA spectra.

Main Results:

• Achieved computational efficiency similar to weak-pulse TA simulations.
• Successfully simulated strong-pump TA spectra for pyrazine.
• Demonstrated that pump pulse intensity can alter the relative intensities of ground-state bleach, stimulated emission, and excited-state absorption signals.

Conclusions:

• The developed protocol provides an efficient and accurate means to simulate strong-pump TA signals.
• This method allows for the control and tuning of spectral features by varying pump pulse intensity.
• Offers new possibilities for understanding molecular dynamics under strong laser fields.