Doubly excited 5s5p(3P1)np autoionizing Rydberg states of indium

The doubly excited 5s5p(P-3(1))np autoionizing Rydberg states of In have been studied for principal quantum number n ranging from 16 to 30, lying similar to 5.3 eV above the first ionization limit. The experiment was achieved with a resonant three-photon excitation in combination with the isolated core excitation method. The resulting spectra exhibit an occurrence of five series. Precise measurements of the resonance frequencies yield the values of quantum defects and series Limits, allowing us to assign them as the autoionizing Rydberg series converging to one of the F' = 7/2, 9/2; and 11/2 hyperfine structures of the In+ 5s5p P-3(1) state. The observation of the hyperfine effects of the autoionizing resonances is made possible through their narrow linewidth.