Electron Emission of Gas-Phase [Au₂₅(SG)₁₈-6H]⁷⁻ Gold Cluster and Its Action Spectroscopy

Abstract

A colloidal solution of Au25(SG)18-protected metal gold clusters was electrosprayed. [Au25(SG)18-6H]7− was selected, stored in a quadrupole ion trap, and irradiated with a UV−vis tunable laser. The excess charges are due to the deprotonation of six COOH moieties and a net charge of −1 on the Au core. Photoexcitation of this species results in electron detachment. The action spectrum obtained by recording the electron detachment yield as a function of the laser wavelength displays a strong decrease as the photon energy decreases and the onset of a band at around 650 nm. This spectrum is compared with the absorption spectrum recorded for Au25(SG)18 in solution. We also show that electron detachment is a one-photon process and likely involves, at low photon energy, ionization by tunneling through a repulsive coulomb barrier.