Effects of electric fields on doubly excited autoionizing Rydberg states of barium

We report the effects of static electric fields on the doubly excited $6p_{\frac{1}{2}}\mathrm{nl}$ states of barium in the region $n^{*}=12\mathrm{}$. Using a three-step laser excitation scheme we have measured the electric-field dependence of the positions and autoionization widths of the $6p_{\frac{1}{2}}-17s,16p,15d,12l \mathrm{}(l=4-10\mathrm{}),12f, \mathrm{and} 16s$ states at field values of up to 4.92 kV/cm. The photoexcitation spectra of the autoionizing states exhibit interference effects which are well understood and provide a better understanding of the character of these states in electric fields. The systematic study of the spectra and positions allows us to explain the field dependence of the autoionization widths in terms of electric-field mixing of the discrete portions of the auoionizing states. The relationship of these effects to dielectronic recombination rates of ions and electrons in plasma microfields is discussed.