Symmetry-induced long-lived excited state inAu6−

We present time-resolved photoelectron spectra in combination with quantum chemical calculations based on time-dependent density functional theory for the study of the long-lived excited state of ${\mathrm{Au}}_{6}^{\ensuremath{-}}$. The experimental spectra indicate an excited state lifetime of at least $90\phantom{\rule{0.3em}{0ex}}\mathrm{ns}$. It is shown that the orbital symmetry of the photoexcited state as well as the planarity of ${\mathrm{Au}}_{6}^{\ensuremath{-}}$ are responsible for the unusual long lifetime. A possible decay mechanism is the fluorescence of a photon which is estimated to take place on a time scale of $730\phantom{\rule{0.3em}{0ex}}\mathrm{ns}$.