The study of Eu 4f(7) 6p6d autoionizing states with RIS and VMI techniques

The spectra and dynamic properties of Eu 4f(7)6p6d autoionizing states are studied systematically with the resonance-ionization spectroscopy (RIS) and the velocity-map imaging (VMI) techniques. The RIS technique is utilized to obtain the spectra of Eu 4f(7)6p6d autoionizing states with the three-step excitation, while the VMI technique is used to detect the dynamic process of autoionization, from which the branching ratio (BR) of ions and the angular distribution (AD) of ejected electrons from Eu 4f(7)6p6d autoionizing states are achieved. Not only the energy levels, line width and line shape are obtained, but also the q-reversal phenomenon is observed in the autoionization spectra. The BR represents energy distribution (ED) of ions by observing the radical information of the VMI image, while the AD, characterized by anisotropy parameters, reveals the differential cross-section of autoionization extracted from the angular information of the VMI image. Furthermore, the variation of BR and AD are analyzed within the entire region of autoionization resonance. Based on the results of BR between 4f(7)6s(+) and 4f(7)5d(+) ionic states, the possibility of the population inversion is discussed.