Autoionizing Distribution of the Triply Excited Double Rydberg States in La Atom

The autoionization distribution o f the triply excited double Rydberg states (TEDRS) 5d_5/2NLnl (N ≤ 2 2 ; n≤ 50; L, l < 4) of La has been investigated by using five-laser resonance excitation in combination with a method of sequential ionization by a pulsed electric field and a constant electric field. The experimental results exhibit that the La atoms in TEDRS predominantly single-autoionize to the ionic Rydberg states located in a few Rydberg manifolds. Furthermore, a difference of autoionization mechanisms between TEDRS above and those below the double ionization threshold is found.