Ionization and fragmentation of autoionizing Rydberg states inNa2

We have studied ionization and fragmentation of ${\mathrm{Na}}_2$ via two-photon excitation of high-lying Rydberg states and absorption of one more photon. Using kinetic energy analysis of the fragments we see novel structures in the abundance of slow ${\mathrm{Na}}^{+}$ below the ionization thresholds for the different vibrational states of the ${\mathrm{Na}}_2^{+}$ core. Several processes are considered to be responsible for the observed spectra, revealing a close connection between autoionization, electronic excitation of the core, and fragmentation.