ABNORMAL BRANCHING RATIOS IN LASER-EXCITED RYDBERG SERIES OF YB+, BA+, AND SR+

Using excitation from five dye lasers, the Yb+ Rydberg series of np(1/ 2) and np(3/2) have been achieved. Abnormal branching ratios of np(1/2 ):np(3/2) excited from Yb+ 7s(1/2) are found. In the relativistic cent ral-field independent-particle approximation, oscillator-strength dist ributions of Yb+, Ba+, and Sr+ are calculated, respectively. The calcu lated results are in good agreement with our experiment on Yb+ and pre vious experiments on Ba+ and Sr+ where abnormal branching ratios were also found. We have found that the abnormal branching ratios are due t o the appearance of Cooper minima or shape resonances. The results can be used to estimate the oscillator strength of unsymmetric double Ryd berg states.