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Laser-induced dynamic alignment of the HD molecule without the Born-Oppenheimer approximation
L Adamowicz1, S Kvaal1, C Lasser1
1Centre for Advanced Study at the Norwegian Academy of Science and Letters, Drammensveien 78, N-0271 Oslo, Norway.
The Journal of Chemical Physics
|October 15, 2022
Summary
This study demonstrates molecular alignment emerging from non-Born-Oppenheimer quantum dynamics simulations for the first time. Researchers developed a method to define alignment without the Born-Oppenheimer approximation, crucial for understanding molecular structure.
Area of Science:
- Quantum Dynamics
- Molecular Physics
- Computational Chemistry
Background:
- The Born-Oppenheimer approximation is standard for laser-induced molecular alignment.
- Deviations from the Born-Oppenheimer approximation challenge the definition of molecular structure and alignment.
Purpose of the Study:
- To demonstrate the emergence of molecular alignment from non-Born-Oppenheimer quantum dynamics simulations.
- To develop a method for defining alignment using non-Born-Oppenheimer wave functions.
- To investigate the behavior of the HD molecule under ultrashort laser pulses beyond the Born-Oppenheimer approximation.
Main Methods:
- Performed the first non-Born-Oppenheimer quantum dynamics simulations for a few-body system (HD molecule).
- Utilized ultrashort laser pulses to induce molecular alignment.
- Developed a pseudo-proton coordinate operator to extract alignment from non-Born-Oppenheimer wave functions, mimicking Born-Oppenheimer definitions.
- Employed time-independent explicitly correlated Gaussian basis functions with a variational, electric-field-dependent construction procedure.
- Validated the basis-set construction against grid-based simulations for model systems.
Main Results:
- Successfully demonstrated the emergence of molecular alignment from non-Born-Oppenheimer simulations.
- Developed a robust method to define and quantify alignment in the non-Born-Oppenheimer regime.
- The chosen basis set approach efficiently captured polarization effects on nuclear and electronic degrees of freedom.
- Validation confirmed the accuracy of the computational approach.
Conclusions:
- Molecular alignment can be meaningfully defined and simulated even beyond the Born-Oppenheimer approximation.
- This work provides a new theoretical framework for studying molecular dynamics where the Born-Oppenheimer approximation breaks down.
- The developed methods are applicable to complex few-body systems interacting with intense laser fields.
