Effect of spin-orbit coupling on strong field ionization simulated with time-dependent configuration interaction

Area of Science:

• Computational Chemistry
• Quantum Dynamics
• Atomic and Molecular Physics

Background:

• Strong field ionization (SFI) is crucial for understanding matter-laser interactions.
• Spin-orbit coupling (SOC) influences electronic states, potentially altering SFI rates, especially in heavy-atom molecules.
• Previous methods like Configuration Interaction with Single excitations (CIS) and CIS with Ionization (CISD-IP) have limitations for degenerate states.

Purpose of the Study:

• To investigate the influence of spin-orbit coupling on the strong field ionization of molecules containing heavy atoms.
• To analyze the impact of SOC on the angular dependence and spectral features of ionization.
• To develop and apply a computational method that accurately treats ionization of degenerate states with SOC.

Main Methods:

• Time-dependent configuration interaction with a complex absorbing potential was employed.
• Spin-orbit coupling was incorporated using an effective one-electron SOC operator, with optimized effective nuclear charges for various ions (Ar+, Kr+, Xe+, HX+).
• The study analyzed ionization dynamics for hydrogen halides (HX) and their cations (HX+) under static and intense laser fields.

Main Results:

• Spin-orbit coupling significantly affects SFI rates, particularly for ionization from π orbitals in HX+.
• Oscillations between 2Π3/2 and 2Π1/2 states were observed in HX+ under static fields.
• Ionization by a two-cycle circularly polarized pulse showed distinct spectral peaks (one or two) depending on the pulse's orientation relative to the molecular axis, attributed to differing ionization rates from π and σ orbitals.

Conclusions:

• Spin-orbit coupling is a critical factor in accurately simulating strong field ionization for molecules with heavy atoms.
• The developed method provides a robust framework for studying SOC effects on ionization dynamics.
• Understanding these effects is essential for interpreting experimental SFI data and advancing molecular attosecond science.