Charged cores in ionized He-4 clusters II: Ab initio calculations for the He-2(+)+He system and Many-Body fitting of the computed points

摘要

Experimental and theoretical studies in large, ionized helium clusters have suggested the presence of structures in which a diatomic (and occasionally triatomic) charged molecular core is surrounded by nearly neutral atoms which are bound to it by weaker forces. The understanding of the interactions between the He-2(+) system and one of the neutral He atoms of the cluster is therefore crucial in order to understand the microscopic dynamics of the post-ionization evolution. The first part of this work [Eur. Phys. J. D 21, 323 (2002)] reported the Potential Energy Surface (PES) for the interaction between the He-2(+) and an He atom and described its bound states. Since dynamical calculations require a more extensive variable range of the relevant PES to be sampled, we present here a further, more detailed study in which we span a larger configurational space for the three internal coordinates of the title system. In particular, we have included a greater range of internuclear distances of the molecular ion. The resulting ab initio values have been numerically fitted via an analytic expression in terms of the three internuclear distances within the He-3(+) system. As a first step in the analysis of the dynamics we have calculated the vibrational coupling terms which involve the ionic core vibrational wave functions and the interaction of the latter molecule with the external helium atom. They reveal interesting features and properties that are here discussed.