Bound, 7snp ¹P₁⁰ series in Ra I: Measurements and predictions

Absorption measurements of the 7s13p-7s52p 1P10 Rydberg series in Ra I are presented. A value of the first ionisation limit (42573.36+or-0.02 cm-1) is derived. From these measurements and from a systematic trend in Ca I, Sr I and Ba I a multichannel quantum defect theory (MODT) analysis is used to predict the location of the 7s9p-7s12p and 6d7p 1P10 states.