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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.