Lifetime measurements using two-step laser excitation for high-lying even-parity levels and improved theoretical oscillator strengths in Y _II

We report new time-resolved laser-induced fluorescence lifetime measurements for 22 highly excited even-parity levels in singly ionized yttrium (Y _II). To populate these levels belonging to the configurations 4d6s, 5s6s 4d5d, 5p², 4d7s and 4d6d, a two-step laser excitation technique was used. Our previous pseudo-relativistic Hartree-Fock model (Biémont et al. 2011) was improved by extending the configuration interaction up to n = 10 to reproduce the new experimental lifetimes. A set of semi-empirical oscillator strengths extended to transitions falling in the spectral range λλ194-3995 nm, depopulating these 22 even-parity levels in Y _II, is presented and compared to the values found in the Kurucz's data base (Kurucz 2011).