Barium autoionizing states in dc electric fields near the second ionization threshold

Abstract

Experimental measurements of the autoionizing spectrum of barium in dc electric fields are presented. The experiments are performed with two pulsed dye lasers, which are used to populate and photoionize the doubly excited 5d6p3D1 state. The photo ion signal is monitored while the ionizing laser frequency is scanned across a field ionization threshold lying below the second (zero-field) ionization threshold. Of particular interest is the investigation of doubly excited states that lie near the second ionization threshold in a dc electric field when the zero field autoionization rate and the field ionization rate are comparable. These experimental results will be compared with theoretical calculations now in progress. The theoretical results are obtained from R-matrix eigenchannel calculations combined with a multichannel quantum defect theory (MQDT) treatment. A frame transformation theory1 is used to calculated amplitudes and phases of hydrogen-Stark wave functions that provide the asymptotic boundary conditions used in the MQDT treatment.