On the metastable level in Ni-like ions

The lowest excited level in Ni-like ions, 3d94s 3D3, decays only via a magnetic octupole (M3) decay. We present calculated values of transition wavelengths and rates for ions with 30 ⩽ Z ⩽ 100. We have observed this line in Xe26+, using the Livermore EBIT-I electron beam ion trap and a microcalorimeter, as well as a high-resolution flat-field grating spectrometer.