New spectroscopic data on even-parity autoionization states for two-color two-step photoionization of nickel atom

The development of collinear resonance ionization spectroscopy for studying the nuclear structure of nickel isotopes far from the stability line relies on high-efficiency two-color two-step photoionization pathways. We systematically investigated the even-parity autoionization spectrum of atomic nickel through resonance ionization mass spectrometry (RIMS). Fifteen intense single-color photoionization lines and corresponding transitions in the 300–325 nm range were identified and excluded as potential interference peaks for subsequent two-color studies. Fifty-one even-parity autoionization states in the 64000–66800 cm⁻¹ range were identified for the first time by scanning from five intermediate excited states of the 3d⁸(³F)4s4p(³P^o) configuration. Forty-eight of these states were assigned unique total angular momentum quantum numbers (J) based on electric dipole transition selection rules. The autoionization state at 64437.77 cm⁻¹ was identified as an optimal final state for enhancing photoionization efficiency in two-color two-step pathways. This study provides comprehensive datasets of even-parity autoionization states of nickel, supporting both the advancement of collinear resonance ionization spectroscopy for exotic nickel isotopes and theoretical modeling of autoionization states. The datasets are openly available at https://doi.org/10.57760/sciencedb.j00113.00280.