Time-Resolved Measurement of Interatomic Coulombic Decay Induced by Two-Photon Double Excitation of Ne2

The hitherto unexplored two-photon doubly excited states [Ne* (2p(-1)3s)](2) were experimentally identified using the seeded, fully coherent, intense extreme ultraviolet free-electron laser FERMI. These states undergo ultrafast interatomic Coulombic decay (ICD), which predominantly produces singly ionized dimers. In order to obtain the rate of ICD, the resulting yield of Ne-2(+) ions was recorded as a function of delay between the extreme ultraviolet pump and UV probe laser pulses. The extracted lifetimes of the long-lived doubly excited states, 390(-130/+450) fs, and of the short-lived ones, less than 150 fs, are in good agreement with ab initio quantum mechanical calculations.