Odd-parityJ=11∕2autoionizing Rydberg series of europium below the5dD49threshold: Spectroscopy and multichannel quantum-defect-theory analysis

Abstract

The odd-parity $J=11∕2$ autoionizing states of europium atom below the $5d$ $^{9}D_{4}$ threshold are investigated by a two-step laser photoionization scheme via the $4{f}^{7}5d6p$ $^{10}F_{9∕2}$ intermediate state. The observed resonances are classified into two autoionizing Rydberg series (with $n=15$ to 55) converging to the $5d$ $^{9}D_{4}$ limit and eight members ($n=13$ to 20) of two autoionizing Rydberg series converging to the higher $5d$ $^{9}D_{5}$ limit. The single series converging to the $5d$ $^{9}D_{3}$ limit is not efficiently excited. The observed four Rydberg series are assigned in $jj$ coupling as $5dnd$ $(4,j)$ and $5dnd$ $(5,j)$ with $j=3∕2$ and $5∕2$. Apart from the $5dnd$ $(5,5∕2)$ series, the majority of autoionizing resonances exhibits narrow linewidths and quasisymmetric line shapes, reflecting this way the weak coupling between the discrete levels and the adjacent continua. The experimental data are analyzed through the semiempirical phase-shifted multichannel quantum defect theory. The theoretically calculated energy level positions and excitation profiles are in good agreement with the experimental ones, thus confirming the identification of the observed structures. The constructed Lu-Fano plot and computed admixture coefficients reveal weak and localized interactions among the Rydberg series members.