Shifts in the ESR spectra of alkali-metal atoms (Li, Na, K, Rb) on helium nanodroplets

Solvation and spectral line shifts of chromium atoms in helium droplets based on a density functional theory approach

The interaction of an electronically excited, single chromium (Cr) atom with superfluid helium nanodroplets of various size (10 to 2000 helium (He) atoms) is studied with helium density functional theory. Solvation energies and pseudo-diatomic potential energy surfaces are determined for Cr in its ground state as well as in the y⁷P, a⁵S, and y⁵P excited states. The necessary Cr–He pair potentials are calculated by standard methods of molecular orbital-based electronic structure theory. In its electronic ground state the Cr atom is found to be fully submerged in the droplet. A solvation shell structure is derived from fluctuations in the radial helium density. Electronic excitations of an embedded Cr atom are simulated by confronting the relaxed helium density (ρ_He), obtained for Cr in the ground state, with interaction pair potentials of excited states. The resulting energy shifts for the transitions z⁷P ← a⁷S, y⁷P ← a⁷S, z⁵P ← a⁵S, and y⁵P ← a⁵S are compared to recent fluorescence and photoionization experiments.