Electron Binding in a Superatom with a Repulsive Coulomb Barrier: The Case of [Ag<sub>44</sub>(SC<sub>6</sub>H<sub>3</sub>F<sub>2</sub>)<sub>30</sub>]<sup>4–</sup> in the Gas Phase
Yuriko Tasaka, Katsunosuke Nakamura, Sami Malola, Keisuke Hirata, Kuenhee Kim, Kiichirou Koyasu, Hannu Häkkinen, Tatsuya Tsukuda
Abstract
The electron binding mechanism in [Ag44(SC6H3F2)30]4– (SC6H3F2 = 3,4-difluorobenzenethiolate) tetra-anion was studied by photoelectron spectroscopy (PES), collision-induced dissociation mass spectrometry (CID-MS), and density functional theory (DFT) computations. PES showed that [Ag44(SC6H3F2)30]4– is energetically metastable with respect to electron autodetachment {[Ag44(SC6H3F2)30]3– + e–} and features a repulsive Coulomb barrier (RCB) with a height of 2.7 eV. However, CID-MS revealed that [Ag44(SC6H3F2)30]4– does not release an electron upon collisional excitation but undergoes dissociation. DFT computations performed on the known structure of [Ag44(SC6H3F2)30]4– confirmed the negative adiabatic electron affinity of [Ag44(SC6H3F2)30]3– and interpreted the experimental PE spectrum by taking into account tunneling electron photodetachment through the RCB.