Selecting two-photon sequential ionization pathways in H₂ through harmonic filtering

Area of Science:

• Physical Chemistry
• Quantum Dynamics
• Molecular Physics

Background:

• Attosecond pulse trains (APTs) combined with femtosecond infrared (IR) pulses enable tracking and control of molecular excitation and ionization on attosecond timescales.
• The interplay of electron and nuclear motion is crucial in light-induced molecular transitions, with inter-pulse time delay serving as a control parameter.
• Understanding and controlling these dynamics are key to manipulating chemical reactions at the fundamental level.

Purpose of the Study:

• To present *ab initio* simulations on the hydrogen molecule (H2) to demonstrate advanced control over photochemical reactions.
• To show how filtering high harmonics in APTs can selectively quench or enhance specific quantum pathways.
• To investigate the discrimination of sequential two-photon ionization processes and steer electron emission direction.

Main Methods:

• Utilized *ab initio* quantum dynamics simulations for the hydrogen molecule.
• Employed attosecond pulse trains (APTs) filtered by frequency.
• Analyzed the effects of time delay and frequency filtering on excitation, ionization, and electron emission.

Main Results:

• Demonstrated that filtering high harmonics in APTs can dictate reaction outcomes by controlling quantum paths.
• Successfully discriminated between sequential two-photon ionization processes (excitation-ionization vs. ionization-excitation).
• Showed that frequency filters can steer one- and two-photon yields to favor directional electron emission.

Conclusions:

• Frequency filtering of APTs offers a powerful method to control quantum pathways in molecular dynamics.
• This technique allows for precise manipulation of reaction outcomes and discrimination of ionization sequences.
• The findings open new avenues for controlling electron emission directionality in molecular systems.