Dynamic Properties Of Eu 4f⁷6p_1/2nd Autoionization Process

The branching ratios of ions and the angular distributions of electrons ejected from the Eu 4f⁷6p_1/2nd autoionizing states are investigated with the velocity-map-imaging technique.To populate the above autoionizing states,the relevant bound Rydberg states have to be detected first.Two new bound Rydberg states are identified,from which autoionization 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 autoionizing states to different final ionic states and the angular distributions of electrons ejected from these processes are measured systematically.To investigate the 4f⁷6p_1/2nd autoionizing states,it is prefer to use the three step isolated core excitation?ICE?method,which has been utilized extensively in studies of alkaline-earth and rare-earth atoms,and has several advantages:1)only low power is required for each excitation laser;2)the spectrum obtained by ICE is simple,where interference effects can be reduced significantly for lower-n states;3)the n values of the 4f⁷6p_1/2nd autoionizing states are determined by the 4f⁷6 snd states,which is the initial states of the third-step excitation,4f⁷6snd?4f⁷6p_1/2nd.However,since the 4f⁷6 snd states have been known for n=6 and 7 only,one has to begin with detecting the 4f⁷6 snd states?n > 6?for studying the 4f⁷6p_1/2nd?n > 6?autoionizing series.To detect the 4f⁷6 snd states in a certain region,a two color three photons resonant ionization method is employed.Furthermore,three different paths are designed to uniquely determine the total angular momentum of 4f⁷6 snd states.Comparisons among the spectra obtained with above three excitation schemes can assign a unique J0 value to any 4f⁷6 snd state detected.However,there are only seven highly excited states can be excited to autoionizing states through ICE method.Since ? values of 4f⁷6snd?n=6,7?states are in the range of2.79².90,two new electron configurations,4f⁷6s8 d and 4f⁷6s9 d,can be identified.More interestingly,in these three excitation schemes,the Eu atom quickly decays to4f⁷5d+?7Do?,4f⁷5d+?9Do?,4f⁷6s+?7So?or 4f⁷6s+?9So?ionic state with the ejection of an electron.Electrons produced in the interaction region are focused by a suitable electron lens and impacted onto the PSD.The fluorescence from the PS is captured by the CCD camera and transferred to a computer for the further data analysis.Based on the above facts,a systematic study of the spectra,the BR and the AD of the4f⁷6p_1/2nd autoionizing states,taking n=6-9 for instance,with the VMI technique is a significant task.Energy dependence of branching ratios and anisotropy parameters within the autoionization spectra are carefully analyzed,followed by a qualitative interpretation.