Magic Numbers in Boson 4He Clusters: The Auger Evaporation Mechanism.

Elena Spreafico,Oleg Kornilov,Giorgio Benedek,Jan Peter Toennies

doi:10.3390/molecules26206244

Abstract

The absence of magic numbers in bosonic 4He clusters predicted by all theories since 1984 has been challenged by high-resolution matter-wave diffraction experiments. The observed magic numbers were explained in terms of enhanced growth rates of specific cluster sizes for which an additional excitation level calculated by diffusion Monte Carlo is stabilized. The present theoretical study provides an alternative explanation based on a simple independent particle model of the He clusters. Collisions between cluster atoms in excited states within the cluster lead to selective evaporation via an Auger process. The calculated magic numbers as well as the shape of the number distributions are in quite reasonable agreement with the experiments.

Highlights

Van der Waals interatomic bonds are the weakest in nature and, unlike covalent bonds, are isotropic, the atomic clusters of heavy rare gases tend to grow in close-packed icosahedral shapes, with magic numbers determined by pure geometrical constraints [1]
It is important to note that the Auger evaporation bility regions) of boson clusters
It is important to note that the Auger evaporation ap‐

Summary

Introduction

Van der Waals interatomic bonds are the weakest in nature and, unlike covalent bonds, are isotropic, the atomic clusters of heavy rare gases tend to grow in close-packed icosahedral shapes, with magic numbers determined by pure geometrical constraints [1]. Not so for 4 He clusters: in view of their liquid and generally superfluid state, magic numbers would seem to be unlikely. Several calculations based on different Monte Carlo methods [3,4,5,6,7] that the binding energy per atom ε( N ) of small 4 He clusters, and in general for boson clusters [8], is a smooth monotonic function of the atom number N. High-resolution matterwave diffraction experiments by Brühl et al [7,9] have shown that the abundance ρ(N) of

Theory

He clusters individual

3.3.Conclusions