The even-parity J=0 autoionizing spectrum of strontium below the 4d5/2threshold: observation and theoretical analysis

Abstract
The even parity J=0, 1 and 2 autoionizing spectra of Sr have been observed below the 4d5/2 threshold using two-step laser spectroscopy from the ground state atom 5s2 in an atomic beam. Resonant excitations of the autoionizing states are observed by time-of-flight (TOF) analysis of the produced ions. In this experiment via the 4d5p 1P1 intermediate level, the J=0 resonances are selectively identified among the other J=1 or 2 ones by comparing the line intensities from two spectra recorded with pi pi and pi sigma polarizations of the two laser beams. From the J=0 data, the J=0 4d3/2 nd3/2 and 4d52/nd5/2 series are observed up to n=66 and 64 respectively. In addition the authors also observed the 5p2 1S0level, whose location has been controversial for a long time: this level is now identified with a broad autoionizing resonance at 54 451+or-30 cm-1 . It has also been observed in this work by a direct two-photon excitation.

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