Imaging the electronic structure of valence orbitals in the XUV ionization of aligned molecules

We present measurements of photoelectron angular distributions (PADs) for the ionization of aligned CO2 molecules by an extreme ultraviolet laser pulse (17-45 eV) that is produced via high-harmonic generation, and that is polarized perpendicularly to the alignment laser axis. Differential PADs are recorded by taking the difference between two measurements for aligned and anti-aligned molecules. The results are compared with ab initio multi-channel R-matrix calculations, which are extended to include the computation of PADs. The calculations agree very well with the experiment, and are resolved with respect to the internal state of the ion and the polarization of the ionizing laser field relative to the molecular frame. For a sufficiently high, but experimentally achievable degree of alignment, the nodal structure of the molecular orbital becomes visible in the PAD.