First observation of doubly charged negative gold cluster ions

Singly charged gold cluster anions in the size range n = 16 - 30 have been captured, stored and size selected in a Penning trap. After application of an electron beam doubly charged gold cluster anions have been observed for 20 less than or equal to n less than or equal to 30. To our knowledge this is the first observation of metal cluster dianions. The threshold appearanc e size is in good agreement with a simple charged sphere model. The applica tion of argon gas pulses simultaneously with the electron beam is found to increase the production rate by an order of magnitude.