Ca+ Ions Solvated in Helium Clusters |
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Authors: | Massimiliano Bartolomei Paul Martini Ricardo Prez de Tudela Toms Gonzlez-Lezana Marta I Hernndez Jos Campos-Martínez Javier Hernndez-Rojas Jos Bretn Paul Scheier |
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Institution: | 1.Instituto de Física Fundamental (IFF-CSIC), Serrano 123, 28006 Madrid, Spain; (M.B.); (J.C.-M.);2.Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Technikerstr. 25, A-6020 Innsbruck, Austria;3.Lehrstuhl für Theoretische Chemie, Ruhr-Universität Bochum, 44780 Bochum, Germany;4.Departamento de Física and IUdEA, Universidad de La Laguna, 38205 Tenerife, Spain; (J.H.-R.); (J.B.) |
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Abstract: | We present a combined experimental and theoretical investigation on Ca ions in helium droplets, HeCa. 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 HeCa -obtained via high-resolution mass spectrometry- generally decrease with N with a more pronounced drop between and , the computed quantum HeCa 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 , which corresponds to the maximum number of atoms in that shell. Behavior of the evaporation energies and radial densities suggests liquid-like cluster structures. |
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Keywords: | molecular clusters solvation helium-alkaline earth ion interactions helium nanodroplets mass spectrometry classical/quantum monte carlo calculations |
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