C. Di Paola

Raman spectra of (He)N-Br2(X) clusters: The role of boson/fermion statistics in a quantum solvent

The aim of this paper is to elucidate the role played by the bosonic/fermionic character of N He atoms solvating a Br2(X) molecule. To this end, an adiabatic model in the molecular stretching coordinate is assumed and the ground energy levels of the complexes are searched by means of Hartree (or Hartree-Fock) Quantum Chemistry calculations for 4He (or 3He) solvent atoms. Simulations of vib-rotational Raman spectra point at the spin multiplicity as the main feature responsible for the drastic difference in the rotational structures of molecules embedded in boson or fermion helium drops as already observed by the experiments of Grebenev et al. [S. Grebenev, J. P. Toennies, and A. F. Vilesov, Science 279 (1998) 2083].

Quantum and classical structures for 4He clusters with the H− impurity

The structural properties and the energetics of some of the smaller HenH− clusters, with n varying from 2 to 14, are examined both with classical and quantum treatments, making also a comparison with the corresponding neutral systems Hen. The results of the calculations, the physical reliability of the employed interaction modeling, and the comparison with previous results are discussed. The emerging picture shows that for clusters of this size the dopant ion H− always locates itself outside the Hen moiety.

Microsolvation of Li(+) in Small He Clusters. Li(+)Hen Species from Classical and Quantum Calculations.

A structural study of the smaller Li(+)Hen clusters with n ≤ 30 has been carried out using different theoretical methods. The structures and the energetics of the clusters have been obtained using both classical energy minimization methods and quantum Diffusion Monte Carlo. The total interaction acting within the clusters has been obtained as a sum of pairwise potentials:  Li(+)-He and He-He. This approximation had been shown in our earlier study to give substantially correct results for energies and geometries once compared to full ab initio calculations. The general features of the spatial structures, and their energetics, are discussed in details for the clusters up to n = 30, and the first solvation shell is shown to be essentially completed by the first 8-10 helium atoms.

Structural and quantum effects from anionic centers in rare gas clusters: The (Ne)nH− and (Ne)n+1 systems

The structural properties and the energetics of some of the smaller ionic clusters of neon atoms with the atomic impurity H−, NenH− with n from 2 up to 8, are examined using different kinds of modeling for the interactions within each cluster and employing different theoretical dynamical approaches, both classical and quantal. The same calculations are carried out also for the corresponding neutral homogeneous clusters Nen+1. The results of the calculations, the physical reliability of the interaction modeling, and the similarities between different features shown by the negative ions with respect to the neutral complexes are discussed. The emerging picture shows that the dopant atom H− always locates itself outside the Nen moiety for clusters of this size without significantly affecting the overall geometries and that many-body (MB) effects within the clusters are rather negligible in the description of the overall interaction potentials.

Replacement equivalence of H− and argon in small (Ar)nH− clusters from optimized structure calculations

The structural properties of some of the smaller ionic clusters of argon atoms containing the atomic impurity H-, ArnH- with n from 2 up to 7, are examined using different modeling for the interactions within each cluster and by employing different theoretical treatments, both classical and quantum, for the energetics. The same calculations are also carried out for the corresponding neutral homogeneous clusters Ar(n+1). The results of the calculations, the physical reliability of the interactions modeling, and the similarities and the difference between the anionic and the neutral complexes are discussed in some detail. The emerging picture shows that, due to specific features of the employed atom-atom potentials, the ArnH- and Ar(n+1) clusters present very similar structures, where the H- dopant substitutes for one of the outer Ar atoms but does not undergo as yet solvation within such small clusters.