Branching ratio and angular distribution of ejected electrons from Eu 4f⁷6p_1/2nd auto-ionizing states

The branching ratios of ions and the angular distributions of electrons ejected from the Eu 4f⁷6p_1/2nd auto-ionizing states are investigated with the velocity-map-imaging technique. To populate the above auto-ionizing states, the relevant bound Rydberg states have to be detected first. Two new bound Rydberg states are identified in the region between 41150 cm^-1 and 44580 cm^-1, from which auto-ionization spectra of the Eu 4f⁷6p_1/2nd states are observed with isolated core excitation method. With all preparations above, the branching ratios from the above auto-ionizing states to different final ionic states and the angular distributions of electrons ejected from these processes are measured systematically. Energy dependence of branching ratios and anisotropy parameters within the auto-ionization spectra are carefully analyzed, followed by a qualitative interpretation.