Resonance-Enhanced Photon Excitation Spectroscopy of the Even-Parity 3p⁵(²P_1/2)nl′ K′J (l′=1, 3) Autoionizing Rydberg States of Ar

Metastable ⁴⁰Ar* atoms are produced in the two metastable states 3p⁵4s3/2₂ and 3p⁵4s′1/2₀ in a pulsed DC discharge in a beam, and are subsequently excited to the even-parity autoionizing resonance series 3p⁵np′ 3/2_1,2, 3p⁵np′ 1/2₁, and 3p⁵nf′ 5/2₃ using single photon excitation with a pulsed dye laser. The excitation spectra of the even-parity autoion-izing resonance series from the metastable ⁴⁰Ar* are obtained by recording the autoionized Ar⁺ ions with time-of-flight ion detection in the photon energy range of 32500-35600 cm^-1 with an experimental bandwidth of <0.1 cm^-1. A wealth of autoionizing resonances are newly observed, from which more precise and systematic spectroscopic data of the level energies and quantum defects are derived.