Effects of Nuclear Hyperfine Mixing on ^{229}Th^{3+} Ions

The triply charged thorium-229 ion (^{229}Th^{3+}) has been identified as a promising candidate for the development of ultraprecise nuclear clocks. In this Letter, we investigate how the electron structure of this ion, particularly the single valence electron, influences the nucleus through nuclear hyperfine mixing (NHM)-a phenomenon previously studied almost solely for highly charged ions. We show that NHM opens electric dipole (E1) transition channels, which can significantly enhance the efficiency of nuclear isomeric excitation by 2 orders of magnitude. Additionally, NHM accelerates the spontaneous decay rate of the nuclear isomeric state by 1% to 7%, depending on the specific hyperfine level involved.