An improved spin-orbit coupling model for use within the effective relativistic coupling by asymptotic representation...

Area of Science:

• Quantum Chemistry
• Theoretical Spectroscopy
• Chemical Physics

Background:

• Accurate potential energy surfaces (PESs) are essential for understanding molecular dynamics.
• Spin-orbit coupling significantly influences the electronic structure and reactivity of molecules, especially in heavy-atom systems.
• Previous models often simplified spin-orbit coupling, limiting accuracy for excited states and complex interactions.

Purpose of the Study:

• To present an improved atomic spin-orbit model within the effective relativistic coupling by asymptotic representation method.
• To enhance the accuracy of coupled potential energy surfaces (PESs) for representing fine structure energies.
• To improve the description of spin-orbit induced conical intersections relevant to photodissociation dynamics.

Main Methods:

• Development of an atomic spin-orbit model incorporating inter-state couplings between different atomic spin-space states.
• Application of the effective relativistic coupling by asymptotic representation method for generating accurate PESs.
• Demonstration using methyl iodide (CH3I) and its photodissociation as a model system.

Main Results:

• The extended model significantly improves the accuracy of PESs, particularly for higher excited states.
• Enhanced accuracy is also observed for low-energy states compared to previous approaches.
• The representation of spin-orbit induced conical intersections, like those in CH3I, is notably improved.

Conclusions:

• The improved atomic spin-orbit model provides more accurate PESs for systems with significant spin-orbit effects.
• This advancement is crucial for reliable simulations of nonadiabatic quantum dynamics in photodissociation processes.
• The method offers a robust framework for treating relativistic coupling effects within an atomic approximation.