OBSERVATION OF THE STARK-EFFECT IN AUTOIONIZING RYDBERG STATES OF AR WITH A MULTICHANNEL QUANTUM-DEFECT ANALYSIS

The Stark spectra of autoionizing Rydberg states of Ar converging to the second ionization limit 3p5 P-2(1/2) 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 nu = 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.