Role of nuclear spin in photoionization: Hyperfine-resolved photoionization of Xe and multichannel quantum defect theory analysis

High-resolution photoionization spectra following single-photon excitation from the ¹S₀ ground state have been recorded for the seven most abundant isotopes of xenon in the range between the first ²P3∕2 and the second ²P1∕2 ionization thresholds. Accurate values for the ionization energies Vᵢₒₙ(²P1∕2) and isotope shifts have been derived enabling the determination of the spin-orbit splitting in Xe⁺ with an unprecedented accuracy. The narrow bandwidth of the vuv laser (250 MHz) has enabled the resolution of the hyperfine structure of the autoionizing ns^' series of ¹²⁹Xe and ¹³¹Xe in the range of principal quantum number n=30--150. Multichannel quantum defect theory (MQDT) has been extended to treat the hyperfine structure of autoionizing Rydberg series and to derive the hyperfine structure of the ²P1∕2 state of the singly charged ion. The MQDT analysis demonstrates the possibility of producing ions in selected hyperfine states by photoionization and enables the characterization of the combined effects of the spin-orbit and hyperfine autoionization.