Authors: Bartolomei, Massimiliano; Martini, Paul; Perez de Tudela, Ricardo; Gonzalez-Lezana, Tomas; Hernandez, Marta I.; Campos-Martinez, Jose; Hernandez-Rojas, Javier; Breton, Jose; Scheier, Paul
Journal: MOLECULES
Publication date: 2021/06/01
DOI: 10.3390/molecules26123642
Abstract: We present a combined experimental and theoretical investigation on Ca+ ions in helium droplets, He N Ca+ . The clusters have been formed in the laboratory by means of electron-impact ionization of Ca-doped helium nanodroplets. Energies and structures of such complexes have been computed using various approaches such as path integral Monte Carlo, diffusion Monte Carlo and basin-hopping methods. The potential energy functions employed in these calculations consist of analytical expressions following an improved Lennard-Jones formula whose parameters are fine-tuned by exploiting ab initio estimations. Ion yields of He N Ca+ -obtained via high-resolution mass spectrometry- generally decrease with N with a more pronounced drop between N = 17 and N = 25 , the computed quantum He N Ca+ evaporation energies resembling this behavior. The analysis of the energies and structures reveals that covering Ca+ with 17 He atoms leads to a cluster with one of the smallest energies per atom. As new atoms are added, they continue to fill the first shell at the expense of reducing its stability, until N = 25 , which corresponds to the maximum number of atoms in that shell. Behavior of the evaporation energies and radial densities suggests liquid-like cluster structures.
