Speaker
Description
Positrons, antiparticles of electrons, have been used as versatile diagnostic tools for characterizations of a wide range of materials. In bulk systems, positrons are trapped by open-volume defects and annihilate with electrons, emitting gamma rays, which allows the non-invasive characterization of materials [1]. By recent advances in experimental techniques, positron-molecule bound states and their lifetimes have been observed for various molecules [2]. Furthermore, the potential use of positrons as probes for molecular conformations was predicted by theoretical studies [3].
In this study, we present theoretical investigations of the positron binding and annihilation properties of water clusters of various sizes using the first-principles calculation. Interactions of positrons with atoms and molecules are often compared and contrasted with those of electrons. In water cluster anions, binding energies of the excess electrons are known to exhibit the specific size dependence and distinct binding properties represented by surface- and interior- bound states. For positron-water complexes, while a water monomer cannot bind a positron, while we revealed that a hydrogen bonded dimer can form an electronically stable positron bound state [4]. The polarization effects induced by the hydrogen bond play a crucial role in enhancing the positron binding abilities of the hydrogen bonded binary molecular clusters. Furthermore, we have also investigated positron-water cluster complexes across a wide range of cluster sizes, and identified surface-localized, internally localized, and strongly delocalized binding features, reflecting the structural characteristics of the hydrogen bond networks. We will present the properties of these positronic complexes, highlighting their dependence on cluster sizes, conformers, and the underlying positron binding mechanisms.
References
[1] F. Tsuomist and I. Makkonen, Rev. Mod. Phys. 85, 1583 (2013).
[2] G. F. Gribakin, J. A. Young, and C. M. Surko, Rev. Mod. Phys. 82, 2557 (2010).
[3] A. Swann and G. F. Gribakin: J. Chem. Phys. 153, 184311 (2020).
[4] D. Yoshida, Y. Kita, T. Shimazaki, and M. Tachikawa, Phys. Chem. Chem. Phys. 24, 26898 (2022).
