Strong-field-induced tunnel ionization of multiple electrons in polyatomic molecules

Molecules in strong optical-frequency fields can exhibit multiple tunneling ionization, leading to explosive coulomb disassembly. Unlike isolated atomic multiple ionization, which is known to be driven by electron recollisions ("Non-Sequential Double Ionization"), multiple ionization in molecules can be induced by laser-driven restructuring of the valence electrons in the molecule. This has been studied for decades in the simplest case of diatomic molecules, and theories such as Charge Resonant Enhanced Ionizaiton (CREI) have been proposed, wherein ionization is dominated by tunneling through transient internal barriers as the atoms move. We have extended these studies to 3- and 4-atom polyatiomic molecules. We find that the additional nuclear degrees of freedom can lead to different mechanisms that also contribute to the structure, enhancement, or suppression of internal tunnleing. Our conclusions relied on observations of the correlated motion of the electrons and ions produced in the interactions, as well as ultrafast x-ray scattering from the valence electronis in strong-field excited systems.