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Triplet Excitons in Small Helium Clusters.
Parmeet Nijjar1, Anna I Krylov1, Oleg V Prezhdo1
1Department of Chemistry , University of Southern California , 3620 McClintock Avenue , Los Angeles , California 90089-1062 , United States.
The Journal of Physical Chemistry. A
|July 2, 2019
Summary
Electrons colliding with liquid helium generate triplet excitons, leading to bubble formation and the creation of helium dimers (He2*). This process involves complex interactions and nonadiabatic transitions.
Area of Science:
- Atomic and Molecular Physics
- Condensed Matter Physics
- Quantum Chemistry
Background:
- Electrons interacting with liquid helium can excite atoms, forming excitons.
- Exciton-atom repulsion can lead to bubble formation around the exciton.
Purpose of the Study:
- To investigate the mechanism of helium dimer (He2*) formation following electron impact on liquid helium.
- To elucidate the role of adiabatic and nonadiabatic processes in exciton dynamics.
Main Methods:
- Performed *ab initio* calculations for adiabatic potential energy surfaces of three-atom systems.
- Conducted dynamics studies using on-the-fly surface calculations.
- Extended calculations to eight-atom systems to validate findings.
Main Results:
- Electron impact creates triplet excitons, causing atomic repulsion and bubble formation.
- Repulsion compresses incipient He2* excitons, driving their evolution towards a potential energy minimum.
- Timescales indicate relevance of three-atom systems to bulk liquid helium dynamics.
Conclusions:
- The study explains He2* creation via electron-impact excitation of helium.
- Highlights the critical role of nonadiabatic transitions in exciton dynamics and He2* formation.
- Emphasizes the interplay between adiabatic potential energy surfaces.
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