Switching from molecular to bulklike dynamics in electronic relaxation of a small gold cluster

Abstract

We have investigated the ultrafast electronic relaxation of Au${}_{7}^{\ensuremath{-}}$ using time-resolved photoelectron spectroscopy combined with first-principles simulations of the excited-state dynamics. Unlike previous findings, which have demonstrated molecularlike excited-state relaxation in Au${}_{7}^{\ensuremath{-}}$ at low excitation energy (1.56 eV), we show here that excitation with 3.12 eV leads to bulklike electronic relaxation without a considerable change of geometry. The experimental findings are fully supported by theoretical simulations, which reveal a bulklike electron-hole relaxation mechanism in a far band-gap cluster. Our findings demonstrate that small gold clusters in the sub-nm size range can exhibit either molecularlike or bulklike properties, depending on the excitation energy.