Ca⁺ Ions Solvated in Helium Clusters

Area of Science:

• Atomic and Molecular Physics
• Quantum Chemistry
• Condensed Matter Physics

Background:

• Helium droplets are unique quantum fluids used to study doped atoms and ions.
• Understanding the solvation of ions in helium provides insights into quantum effects and cluster stability.

Purpose of the Study:

• To investigate the structure and stability of calcium ions (Ca+) solvated in helium nanodroplets (HeNCa+).
• To determine the energetic properties and preferred configurations of HeNCa+ clusters.

Main Methods:

• Experimental: Electron-impact ionization of Ca-doped helium nanodroplets and high-resolution mass spectrometry.
• Theoretical: Path integral Monte Carlo, diffusion Monte Carlo, and basin-hopping methods.
• Potential energy functions derived from ab initio calculations and an improved Lennard-Jones formula.

Main Results:

• Ion yields of HeNCa+ decrease with increasing helium atom number (N), with a significant drop between N=17 and N=25.
• Computed evaporation energies correlate with experimental observations.
• Analysis indicates that clusters with 17 helium atoms exhibit minimal energy per atom, suggesting high stability.
• A maximum of 25 helium atoms can occupy the first solvation shell around Ca+.

Conclusions:

• The study reveals a stable configuration for Ca+ in helium droplets at N=17 atoms.
• Evaporation energies and radial densities suggest liquid-like structures in HeNCa+ clusters.
• The findings contribute to understanding ion-atom interactions and solvation in quantum systems.