Changes of the electronic structure along the internuclear coordinate studied by ultrafast photoelectron spectroscopy: the 21Σu+ Na2 double-minimum state

In a two-color femtosecond pump–probe experiment photoelectron spectra were detected to map the nuclear wave packet in the 21Σu+ Na2 double-minimum state. The wave packet serves as a local probe for the R-dependent ionization probability. The pump photon energy of 3.65 eV allows to access a range of internuclear distances from 3 to 9 Å. The bound 12Σg+ and the repulsive 12Σu+ ionic states are accessible with the probe photon energy of 4.68 eV. Energy-resolved photoelectron measurements permitted to rule out competing ionization pathways. Our results show that for the bound ionic state the ionization probability at the outer turning point is 4.0 ± 0.4 times larger than that at the inner turning point.