1s2s2p23d 6L - 1s2p33d 6D, L=F, D, P Transitions in O IV, F V and Ne VI
  We present observations of VUV transitions between doubly excited sextet states in O IV, F V and Ne VI. Spectra were produced by collisions of an O+ beam with a solid carbon target. We also studied spectra obtained previously of F V and Ne VI. Some observed lines were assigned to the 1s2s2p23d 6L - 1s2p33d 6D, L=F, D, P electric-dipole transitions, and compared with results of MCHF (with QED and higher-order corrections) and MCDF calculations. 42 new lines have been identified. Highly excited sextet states in five-electron ions provide a new form of energy storage and are possible candidates for VUV and x-ray lasers. 
Bin Lin, H. Gordon Berry, Tomohiro Shibata, A. Eugene Livingston,   Henri-Pierre Garnir, Thierry Bastin, and J. Desesquelles