Experimental and theoretical analysis of the 5pnp J = 0~e, 1~e, 2~e autoinonizing spectrum of Sr

摘要

The even parity 5pnp J = 0, 1 and 2 doubly excited autoionizing states of strontium were investigated both experimentally and theoretically. Sr atoms in an atomic beam were excited through the two-step Isolated Core Excitation (ICE) scheme 5s~2 ~1S_0 -λ_1 → 5sn'p ~1P_1 (n' = 12-16) -λ_2 → [5p_(3/2)np]J. The final ICE transition probes the [5p_(3/2)np]J resonances. However, the [5p_(1/2)np]J series below the 5p_(1/2) threshold were excited also due to their mixing with the [5p_(3/2)np]J perturbers. An extended energy region was covered below and above the 5p_(1/2) ionization limit by saturating the central ICE lobe and recording as many as possible "red" and "blue" secondary lobes. J identification was achieved by using mutually parallel and perpendicular linear polarizations of the laser beams. The ICE spectra were compared to those obtained by employing a two-step excitation scheme using the bound 4d5p ~1P_1 valence state as an intermediate one. Final identification for very complex structures was achieved after comparison with theoretical energy level positions and excitation profiles produced by the R-matrix method combined with the multichannel quantum defect theory (MQDT) method. The agreement between theoretical and observed structures is quite satisfactory.