Autoionization inhibited by internal interferences

We have measured the linewidths of [5d_3/2n₂d_3/2]_J=0 autoionizing Rydberg states of barium with principal quantum numbers ranging between n₂=14 and n₂=100. Dramatic deviations of the autoionization rates from the normal n^*-3₂ scaling law have been observed. Whereas the [5d_3/260d_3/2]_J=0 level exhibits a linewidth Γ (FWHM) as low as 6 MHz, higher (n₂~=80) members of this series are broadened up to 5 GHz. Autoionization is inhibited for principal quantum numbers n₂~=60 because of configuration interaction between the [5d_3/2n₂d_3/2]_J=0 and [5d_5/2n₃d_5/2]_J=0 Rydberg series. This causes the state at n₂=60 to be metastable.