First observation of delayed electron emission from dianionic metal clusters

Time-resolved electron emission after photoexcitation in a Penning trap has been applied to size and charge-state selected dianionic gold clusters, Au292−. An exponential decrease of the relative abundance was recorded, along with a corresponding appearance of the monoanion Au291−. This constitutes the first observation of delayed electron emission from a metal-cluster dianion. By application of the Weisskopf decay-rate model to the emission rate the binding energy of the second surplus electron was found to be 0.91(5) eV. This value compares favourably with the second electron affinity as expected from the liquid drop model.