Strong-field ionization of a heteronuclear diatomic molecule

We theoretically study strong-field ionization of a heteronuclear diatomic molecule, CO, by calculating the photoelectron angular distributions (PADs) and the total ionization rates using linearly and circularly polarized laser fields. We find that, although the PADs of CO generally do not have inversion symmetry, they become more inversion symmetric as the photoelectron energy increases. Heteronuclear features of CO upon ionization are better understood by comparing the results with those of a representative of homonuclear molecules, N2, in that, although there are some similarities between CO and N2 due to the same orbital symmetry, σg, there are some differences between them in terms of the ionization suppression and orientation dependence of the total ionization yield. Namely, CO behaves more like an atom in the low-intensity range in a sense that ionization takes place mainly from the neighborhood of the C core, while it behaves more like a double-core molecule in the high-intensity range since ionization takes place from the neighborhood of both C and O cores. This explains why ionization suppression of CO is not seen at the low intensity but it becomes more visible at the high intensity range.