Observation of the Stark effect in autoionizing Rydberg states of Ar with a multichannel quantum-defect analysis

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Abstract
The Stark spectra of autoionizing Rydberg states of Ar converging to the second ionization limit 3p5 2P1/2 have been investigated, experimentally and theoretically, as a function of electric field strength, in the range 15-2000 V cm-1. The levels with effective principal quantum number v=12-19, are excited by single-photon absorption from the ground state using a coherent extreme ultraviolet laser source (bandwidth approximately 1.0 cm-1) generated by four-wave sum-frequency mixing of the outputs of two pulsed dye lasers; a detailed Stark map is obtained for the first time. A multichannel quantum-defect-theory analysis of the field-induced-state mixing is carried out, reproducing positions, widths and shapes of the experimentally observed features. In addition, this analysis provides new insight into the dynamical decay of the autoionizing states.