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. 2021 Oct 15;26(20):6244.
doi: 10.3390/molecules26206244.

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

Elena Spreafico  1 , Giorgio Benedek  1   2 , Oleg Kornilov  3 , Jan Peter Toennies  4
Affiliations

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

Elena Spreafico et al. Molecules. .

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.

Keywords: Auger evaporation; Van der Waals bonds; cluster supersonic jets; helium clusters; magic numbers.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
The Auger processes involving the collision of two atoms in the excited one-particle states Ei and Ej which lead to the emission into a free state Ei’ of either the atom in the state Ei (a) or the atom in the state Ej (b) with the other atom decaying into a lower state Ej’.
Figure 2
Figure 2
Comparison between (a) the (4He)N cluster size distributions obtained from cluster diffraction experiments by Brühl et al. [9] for different source pressures P0, and (b) the theoretical distributions for three different cluster temperatures and for an instrumental angular resolution parameter s = 0.002. Each experimental distribution is divided by a distribution ρfit(N)∝N−α obtained from averaging over the magic-number oscillations with α given by a best fit.
Figure 3
Figure 3
Same as Figure 2 with respect to a linear 1/N scale for a comparison between experiment and theory (T = 0.8 K only) at large values of N: (a) oscillations in cluster abundance and (b) the calculated distribution for 0.8 K.
See this image and copyright information in PMC

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