Resonances and critical points in the strong-field ionization of diatomic molecules

We measured the strong-field ionization of diatomic iodine molecules as a function of wavelength and internuclear separation. The latter was done by launching a wave packet on the B state of iodine and probing the ionization as a function of time delay. As a function of wavelength at fixed internuclear separation and as a function time delay at fixed wavelength, critical points are found where the ionization increases significantly. All of the results are consistent with ionization from deep $\ensuremath{\sigma}$ orbitals and resonant interactions. In conclusion, we present a unified view of the strong-field ionization of diatomic molecules.