Laser spectroscopy of U i using stepwise excitation and fluorescence detection

We report 138 U i odd levels in the region 32 260–34 900 cm−1 and 16 even levels in the region 49500–49900 cm−1. These levels are reached by two- or three-step selective dye laser excitation, respectively, and detected by fluorescence to lower levels. J values are assigned by identifying decays to known lower levels. Unique J values are presented for 64 levels and partial assignment (two possibilities) for 42 levels. A transition array is given indicating 427 fluorescence lines observed in the blue-green region. The exponential time decay of the fluorescence intensity provides direct determination of excited state lifetimes. Radiative lifetimes of 135 levels are presented.