Experimental and theoretical analysis of the 5pnp J = O-e, 1(e), 2(e) autoionizing spectrum of Sr

The even parity 5pnp J = 0, 1 and 2 doubly excited autoionizing states of s trontium were investigated both experimentally and theoretically. Sr atoms in an atomic beam were excited through the two-step isolated Core Excitatio n (ICE) scheme 5s(2) S-1(o) -lambda (1) --> 5sn'p P-1(1) (n' = 12-16) -lamb da (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) thresho ld 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) ionizat ion limit by saturating the central ICE lobe and recording as many as possi ble "red" and "blue" secondary lobes. J identification was achieved by usin g mutually parallel and perpendicular linear polarizations of the laser bea ms. The ICE spectra were compared to those obtained by employing a two-step excitation scheme using the bound 4d5p P-1(1) valence state as an intermed iate one. Final identification for very complex structures was achieved aft er comparison with theoretical energy level positions and excitation profil es produced by the R-matrix method combined with the multichannel quantum d efect theory (MQDT) method. The agreement between theoretical and observed structures is quite satisfactory.