Rydberg molecules at surfaces

A molecule excited to a Rydberg state in the gas phase will interact with a surface in quite a different way from a ground state molecule. The Rydberg electron, in its diffuse high-energy orbital, is highly susceptible to the electric fields near to the surface. The Rydberg molecule also has considerable excess energy (typically >7 eV) to dispose of.

At a metal surface, the very large fluctuating dipole created by the large separation between the Rydberg electron and the ionic core of the molecule, generates an image dipole in the metal. This interaction leads to strong perturbation of the Rydberg energy levels, when the distance from the surface is less than 10 times the Rydberg radius.

The Rydberg electron can tunnel into the conduction band of the metal at sufficiently short distance (three to four times the Rydberg radii) leading to ionization.

Possible processes occurring through the Rydberg–surface interaction

  • Ionization of the Rydberg electron 
  • Induced predissociation (or intramolecular energy transfer processes) of the Rydberg molecule
  • Transfer of the Rydberg energy into chemical bond breaking at the surface
  • Chemical processes through deposition of the Rydberg molecule or its cation or a fragment
  • Reflection of the Rydberg molecule from the surface
  • Auger electron generation as the ion core is neutralised

Interest in this area

  • Study of a novel physical process with many controllable parameters
  • Rydberg states play important role in plasmas – surface boundary conditions important 
  • Understand properties of electronically excited species at surface
  • Observed emission of Rydberg atoms and clusters via thermal desorption (Holmlid et al) from e.g., impregnated metal oxide surfaces
  • Possibility for nanofabrication by lithography or deposition on surfaces using Rydberg atoms guided by optical lattice [Shapiro, Brumer, Metcalf]
  • Novel surface chemistry
  • Characterization of thin films
  • Development of a mirror for atoms/molecular beams
  • Implications for quantum information processing – atom on a chip experiments.

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