Angular Distribution of Molecular Fragments after K-Shell Excitation.

Using polarized and tunable synchrotron radiation, core electrons of simple molecules (N_2, CO, H_2O) are excited to specific states. The angular distribution of fragments from the core-hole excited states is measured by using angle resolved detectors, installed with high pass filters, attached at 0^circ and 90 ^circ positions with respect to the electric field vector of the radiation; this distribution is directly correlated with the orientational distribution of the core-hole excited state and to the symmetry of the core-hole excited state because the recoil dynamics for the fragments, which are measured, are those corresponding to axial recoil fragments due to the short lifetime of the core-hole excited state, and the limited observation to high kinetic energy fragments set by the high pass filters. The present experiment revealed the symmetries for the states corresponding to the rich resonances below the ionization edges, which conventional absorption spectroscopy does not find, and the double excitations, shake-ups, shake -offs, and shape resonances above the ionization edges.