Tunneling, Stark-Shifts, and Nearest Neighbor Effects for Full Valence Shell, Ultrahigh Intensity Laser Ionization of Carbon Monoxide*

The strong and ultrastrong field-molecule interaction is a complex, many-body interaction involving multiple ionization processes. We present experimental ion yields and molecular fragment energies for the ionization of carbon monoxide (¹²C ¹⁶O and ¹³C ¹⁸O) in a laser field with intensities spanning from 10¹⁴ W/cm² to 10¹⁷ W/cm². The work addresses specifically the formation of high charge states corresponding to the complete removal of the valence electrons from carbon and oxygen. Detailed saturation intensities for each ion channel are reported. Our theory model of the ionization includes tunneling, bound state Stark-shifts, nearest neighbor ion Coulomb fields, and the molecular dissociation dynamics. The ion energy spectra (with average energies of 20eV for example with O⁶⁺) show no dependence on the field intensity and are attributed to dissociative molecular ionization. The ionization of the neutral molecule to form the parent ion is shown to have a minimal effect on the formation of the highest charge states beyond initiating enhanced field ionization from the nearest neighbor ions. Atomic-like ionization is observed only when the ionization of the tightly bound ion states is unaffected by nearest neighbor fields.